STRESS-NG(1)

NAME
stress-ng - a tool to load and stress a computer system

SYNOPSIS
stress-ng [OPTION [ARG]] ...

DESCRIPTION
stress-ng will stress test a computer system in various selectable ways. It was designed to exercise various physical subsystems of a computer as well as the various operating system kernel interfaces. stress-ng also has a wide range of CPU specific stress tests that exercise floating point, integer, bit manipulation and control flow.

stress-ng was originally intended to make a machine work hard and trip hardware issues such as thermal overruns as well as operating system bugs that only occur when a system is being thrashed hard. Use stress-ng with caution as some of the tests can make a system run hot on poorly designed hardware and also can cause excessive system thrashing which may be difficult to stop.

stress-ng can also measure test throughput rates; this can be useful to observe performance changes across different operating system releases or types of hardware. However, it has never been intended to be used as a precise benchmark test suite, so do NOT use it in this manner.

Running stress-ng with root privileges will adjust out of memory settings on Linux systems to make the stressors unkillable in low memory situations, so use this judiciously. With the appropriate privilege, stress-ng can allow the ionice class and ionice levels to be adjusted, again, this should be used with care.

One can specify the number of processes to invoke per type of stress test; specifying a zero value will select the number of processors available as defined by sysconf(_SC_NPROCESSORS_CONF), if that can't be determined then the number of online CPUs is used. If the value is less than zero then the number of online CPUs is used.

OPTIONS

General stress-ng control options:

--abort
    this option will force all running stressors to abort (terminate) if any other stressor terminates prematurely because of a failure.

--aggressive
    enables more file, cache and memory aggressive options. This may slow tests down, increase latencies and reduce the number of bogo ops as well as changing the balance of user time vs system time used depending on the type of stressor being used.

-a N, --all N, --parallel N
    start N instances of all stressors in parallel. If N is less than zero, then the number of CPUs online is used for the number of instances. If N is zero, then the number of configured CPUs in the system is used.

-b N, --backoff N
    wait N microseconds between the start of each stress worker process. This allows one to ramp up the stress tests over time.

--change-cpu
    this forces child processes of some stressors to change to a different CPU from the parent on startup. Note that during the execution of the stressor the scheduler may choose move the parent onto the same CPU as the child. The stressors affected by this option are client/server style stressors, such as the network stresors (sock, sockmany, udp, etc) or context switching stressors (switch, pipe, etc).

--class name
    specify the class of stressors to run. Stressors are classified into one or more of the following classes: cpu, cpu-cache, device, gpu, io, interrupt, filesystem, memory, network, os, pipe, scheduler and vm. Some stressors fall into just one class. For example the 'get' stressor is just in the 'os' class. Other stressors fall into more than one class, for example, the 'lsearch' stressor falls into the 'cpu', 'cpu-cache' and 'memory' classes as it exercises all these three. Selecting a specific class will run all the stressors that fall into that class only when run with the --sequential option. Specifying a name followed by a question mark (for example --class vm?) will print out all the stressors in that specific class.

-n, --dry-run
    parse options, but do not run stress tests. A no-op.

--ftrace
    enable kernel function call tracing (Linux only). This will use the kernel debugfs ftrace mechanism to record all the kernel functions used on the system while stress-ng is running. This is only as accurate as the kernel ftrace output, so there may be some variability on the data reported.

-h, --help
    show help.

--ignite-cpu
    alter kernel controls to try and maximize the CPU. This requires root privilege to alter various /sys interface controls. Currently this only works for Intel P-State enabled x86 systems on Linux.

--ionice-class class
    specify ionice class (only on Linux). Can be idle (default), besteffort, be, realtime, rt.

--ionice-level level
    specify ionice level (only on Linux). For idle, 0 is the only possible option. For besteffort or realtime values 0 (highest priority) to 7 (lowest priority). See ionice(1) for more details.

--iostat S
    every S seconds show I/O statistics on the device that stores the stress-ng temporary files. This is either the device of the current working directory or the --temp-path specified path. Currently a Linux only option. The fields output are:
    Column Heading | Explanation
    Inflight | number of I/O requests that have been issued to the device driver but have not yet completed
    Rd K/s | read rate in 1024 bytes per second
    Wr K/s | write rate in 1024 bytes per second
    Dscd K/s | discard rate in 1024 bytes per second
    Rd/s | reads per second
    Wr/s | writes per second
    Dscd/s | discards per second

--job jobfile
    run stressors using a jobfile. The jobfile is essentially a file containing stress-ng options (without the leading --) with one option per line. Lines may have comments with comment text proceeded by the # character. A simple example is as follows:

    run sequential   # run stressors sequentially
    verbose          # verbose output
    metrics-brief    # show metrics at end of run
    timeout 60s      # stop each stressor after 60 seconds
    #
    # vm stressor options:
    #
    vm 2             # 2 vm stressors
    vm-bytes 128M    # 128MB available memory
    vm-keep          # keep vm mapping
    vm-populate      # populate memory
    #
    # memcpy stressor options:
    #
    memcpy 5         # 5 memcpy stressors

    The job file introduces the run command that specifies how to run the stressors:

    run sequential - run stressors sequentially
    run parallel - run stressors together in parallel

    Note that 'run parallel' is the default.

--keep-files
    do not remove files and directories created by the stressors. This can be useful for debugging purposes. Not generally recommended as it can fill up a file system.

-k, --keep-name
    by default, stress-ng will attempt to change the name of the stress processes according to their functionality; this option disables this and keeps the process names to be the name of the parent process, that is, stress-ng.

--klog-check
    check the kernel log for kernel error and warning messages and report these as soon as they are detected. Linux only and requires root capability to read the kernel log.

--ksm
    enable kernel samepage merging (Linux only). This is a memory-saving de-duplication feature for merging anonymous (private) pages.

--log-brief
    by default stress-ng will report the name of the program, the message type and the process id as a prefix to all output. The --log-brief option will output messages without these fields to produce a less verbose output.

--log-file filename
    write messages to the specified log file.

--log-lockless
    log messages use a lock to avoid intermingling of blocks of stressor messages, however this may cause contention when emitting a high rate of logging messages in verbose mode. This option disables log message locking.

--maximize
    overrides the default stressor settings and instead sets these to the maximum settings allowed. These defaults can always be overridden by the per stressor settings options if required.

--max-fd N
    set the maximum limit on file descriptors (value or a % of system allowed maximum). By default, stress-ng can use all the available file descriptors; this option sets the limit in the range from 10 up to the maximum limit of RLIMIT_NOFILE. One can use a % setting too, e.g. 50% is half the maximum allowed file descriptors. Note that stress-ng will use about 5 of the available file descriptors so take this into consideration when using this setting.

--mbind list
    set strict NUMA memory allocation based on the list of NUMA nodes provided; page allocations will come from the node with sufficient free memory closest to the specified node(s) where the allocation takes place. This uses the Linux set_mempolicy(2) call using the MPOL_BIND mode. The NUMA nodes to be used are specified by a comma separated list of node (0 to N-1). One can specify a range of NUMA nodes using '-', for example: --mbind 0,2-3,6,7-11

--metrics
    output number of bogo operations in total performed by the stress processes. Note that these are not a reliable metric of performance or throughput and have not been designed to be used for benchmarking whatsoever. Some stressors have additional metrics that are more useful than bogo-ops, and these are generally more useful for observing how a system behaves when under various kinds of load.

    The following columns of information are output:
    Column Heading | Explanation
    bogo ops | number of iterations of the stressor during the run. This is metric of how much overall "work" has been achieved in bogo operations. Do not use this as a reliable measure of throughput for benchmarking.
    real time (secs) | average wall clock duration (in seconds) of the stressor. This is the total wall clock time of all the instances of that particular stressor divided by the number of these stressors being run.
    usr time (secs) | total user time (in seconds) consumed running all the instances of the stressor.
    sys time (secs) | total system time (in seconds) consumed running all the instances of the stressor.
    bogo ops/s (real time) | total bogo operations per second based on wall clock run time. The wall clock time reflects the apparent run time. The more processors one has on a system the more the work load can be distributed onto these and hence the wall clock time will reduce and the bogo ops rate will increase. This is essentially the "apparent" bogo ops rate of the system.
    bogo ops/s (usr+sys time) | total bogo operations per second based on cumulative user and system time. This is the real bogo ops rate of the system taking into consideration the actual time execution time of the stressor across all the processors. Generally this will decrease as one adds more concurrent stressors due to contention on cache, memory, execution units, buses and I/O devices.
    CPU used per instance (%) | total percentage of CPU used divided by number of stressor instances. 100% is 1 full CPU. Some stressors run multiple threads so it is possible to have a figure greater than 100%.

--metrics-brief
    show shorter list of stressor metrics (no CPU used per instance).

--minimize
    overrides the default stressor settings and instead sets these to the minimum settings allowed. These defaults can always be overridden by the per stressor settings options if required.

--no-madvise
    from version 0.02.26 stress-ng automatically calls madvise(2) with random advise options before each mmap and munmap to stress the vm subsystem a little harder. The --no-advise option turns this default off.

--no-oom-adjust
    disable any form of out-of-memory score adjustments, keep the system defaults. Normally stress-ng will adjust the out-of-memory scores on stressors to try to create more memory pressure. This option disables the adjustments.

--no-rand-seed
    Do not seed the stress-ng pseudo-random number generator with a quasi random start seed, but instead seed it with constant values. This forces tests to run each time using the same start conditions which can be useful when one requires reproducible stress tests.

--oom-avoid
    Attempt to avoid out-of-memory conditions that can lead to the Out-of-Memory (OOM) killer terminating stressors. This checks for low memory scenarios and swapping before making memory allocations and hence adds some overhead to the stressors and will slow down stressor allocation speeds.

--oom-avoid-bytes N
    Specify a low memory threshold to avoid making any further memory allocations. The parameter can be specified as an absolute number of bytes (e.g. 2M for 2MB) or a percentage of the current free memory, e.g. 5% (the default is 2.5%). This option implicitly enables --oom-avoid. The option allows the system to have enough free memory to try to avoid the out-of-memory killer terminating processes.

--oomable
    Do not respawn a stressor if it gets killed by the Out-of-Memory (OOM) killer. The default behaviour is to restart a new instance of a stressor if the kernel OOM killer terminates the process. This option disables this default behaviour.

--page-in
    touch allocated pages that are not in core, forcing them to be paged back in. This is a useful option to force all the allocated pages to be paged in when using the bigheap, mmap and vm stressors. It will severely degrade performance when the memory in the system is less than the allocated buffer sizes. This uses mincore(2) to determine the pages that are not in core and hence need touching to page them back in.

--pathological
    enable stressors that are known to hang systems. Some stressors can rapidly consume resources that may hang a system, or perform actions that can lock a system up or cause it to reboot. These stressors are not enabled by default, this option enables them, but you probably don't want to do this. You have been warned. This option applies to the stressors: bad-ioctl, bind-mount, cpu-online, mlockmany, oom-pipe, smi, sysinval and watchdog.

--perf
    measure processor and system activity using perf events. Linux only and caveat emptor, according to perf_event_open(2): "Always double-check your results! Various generalized events have had wrong values.". Note that with Linux 4.7 one needs to have CAP_SYS_ADMIN capabilities for this option to work, or adjust /proc/sys/kernel/perf_event_paranoid to below 2 to use this without CAP_SYS_ADMIN.

-q, --quiet
    do not show any output.

-r N, --random N
    start N random stress workers. If N is 0, then the number of configured processors is used for N.

--sched scheduler
    select the named scheduler (only on Linux). To see the list of available schedulers use: stress-ng --sched which

--sched-prio prio
    select the scheduler priority level (only on Linux). If the scheduler does not support this then the default priority level of 0 is chosen.

--sched-period period
    select the period parameter for deadline scheduler (only on Linux). Default value is 0 (in nanoseconds).

--sched-runtime runtime
    select the runtime parameter for deadline scheduler (only on Linux). Default value is 99999 (in nanoseconds).

--sched-deadline deadline
    select the deadline parameter for deadline scheduler (only on Linux). Default value is 100000 (in nanoseconds).

--sched-reclaim
    use cpu bandwidth reclaim feature for deadline scheduler (only on Linux).

--seed N
    set the random number generate seed with a 64 bit value. Allows stressors to use the same random number generator sequences on each invocation.

--sequential N
    sequentially run all the stressors one by one for a default of 60 seconds. The number of instances of each of the individual stressors to be started is N. If N is less than zero, then the number of CPUs online is used for the number of instances. If N is zero, then the number of CPUs in the system is used. Use the --timeout option to specify the duration to run each stressor.

--skip-silent
    silence messages that report that a stressor has been skipped because it requires features not supported by the system, such as unimplemented system calls, missing resources or processor specific features.

--smart
    scan the block devices for changes S.M.A.R.T. statistics (Linux only). This requires root privileges to read the Self-Monitoring, Analysis and Reporting Technology data from all block devies and will report any changes in the statistics. One caveat is that device manufacturers provide different sets of data, the exact meaning of the data can be vague and the data may be inaccurate.

--sn
    use scientific notation (e.g. 2.412e+01) for metrics.

--status N
    report every N seconds the number of running, exiting, reaped and failed stressors as well as the current run duration.

--stderr
    write messages to stderr. With version 0.15.08 output is written to stdout, previously due to a historical oversight output went to stderr. This option allows one to revert to the pre-0.15.08 behaviour.

--stdout
    all output goes to stdout. This is the new default for version 0.15.08. Use the --stderr option for the original behaviour.

--stressors
    output the names of the available stressors.

--syslog
    log output (except for verbose -v messages) to the syslog.

--taskset list
    set CPU affinity based on the list of CPUs provided; stress-ng is bound to just use these CPUs (Linux only). The CPUs to be used are specified by a comma separated list of CPU (0 to N-1). One can specify a range of CPUs using '-', for example: --taskset 0,2-3,6,7-11

--temp-path path
    specify a path for stress-ng temporary directories and temporary files; the default path is the current working directory. This path must have read and write access for the stress-ng stress processes.

--thermalstat S
    every S seconds show CPU and thermal load statistics. This option shows average CPU frequency in GHz (average of online-CPUs), the minimum CPU frequency, the maximum CPU frequency, load averages (1 minute, 5 minute and 15 minutes) and available thermal zone temperatures in degrees Centigrade.

--thrash
    This can only be used when running on Linux and with root privilege. This option starts a background thrasher process that works through all the processes on a system and tries to page as many pages in the processes as possible. It also periodically drops the page cache, frees reclaimable slab objects and pagecache. This will cause considerable amount of thrashing of swap on an over-committed system.

-t N, --timeout T
    run each stress test for at least T seconds. One can also specify the units of time in seconds, minutes, hours, days or years with the suffix s, m, h, d or y. Each stressor will be sent a SIGALRM signal at the timeout time, however if the stress test is swapped out, in an uninterruptible system call or performing clean up (such as removing hundreds of test file) it may take a while to finally terminate. A 0 timeout will run stress-ng for ever with no timeout. The default timeout is 24 hours.

--times
    show the cumulative user and system times of all the child processes at the end of the stress run. The percentage of utilisation of available CPU time is also calculated from the number of on-line CPUs in the system.

--timestamp
    add a timestamp in hours, minutes, seconds and hundredths of a second to the log output.

--timer-slack N
    adjust the per process timer slack to N nanoseconds (Linux only). Increasing the timer slack allows the kernel to coalesce timer events by adding some fuzziness to timer expiration times and hence reduce wakeups. Conversely, decreasing the timer slack will increase wakeups. A value of 0 for the timer-slack will set the system default of 50,000 nanoseconds.

--tz
    collect temperatures from the available thermal zones on the machine (Linux only). Some devices may have one or more thermal zones, where as others may have none.

-v, --verbose
    show all debug, warnings and normal information output.

--verify
    verify results when a test is run. This is not available on all tests. This will sanity check the computations or memory contents from a test run and report to stderr any unexpected failures.

--verifiable
    print the names of stressors that can be verified with the --verify option.

-V, --version
    show version of stress-ng, version of toolchain used to build stress-ng and system information.

--vmstat S
    every S seconds show statistics about processes, memory, paging, block I/O, interrupts, context switches, disks and cpu activity. The output is similar that to the output from the vmstat(8) utility. Currently a Linux only option.

-x, --exclude list
    specify a list of one or more stressors to exclude (that is, do not run them). This is useful to exclude specific stressors when one selects many stressors to run using the --class option, --sequential, --all and --random options. Example, run the cpu class stressors concurrently and exclude the numa and search stressors:

    stress-ng --class cpu --all 1 -x numa,bsearch,hsearch,lsearch

-Y, --yaml filename
    output gathered statistics to a YAML formatted file named 'filename'.

Stressor specific options:

--access N
    start N workers that work through various settings of file mode bits (read, write, execute) for the file owner and checks if the user permissions of the file using access(2) and faccessat(2) are sane.

--access-ops N
    stop access workers after N bogo access sanity checks.

--affinity N
    start N workers that run 16 processes that rapidly change CPU affinity (only on Linux). Rapidly switching CPU affinity can contribute to poor cache behaviour and high context switch rate.

--affinity-ops N
    stop affinity workers after N bogo affinity operations.

--affinity-delay N
    delay for N nanoseconds before changing affinity to the next CPU. The delay will spin on CPU scheduling yield operations for N nanoseconds before the process is moved to another CPU. The default is 0 nanosconds.

--affinity-pin
    pin all the 16 per stressor processes to a CPU. All 16 processes follow the CPU chosen by the main parent stressor, forcing heavy per CPU loading.

--affinity-rand
    switch CPU affinity randomly rather than the default of sequentially.

--affinity-sleep N
    sleep for N nanoseconds before changing affinity to the next CPU.

--af-alg N
    start N workers that exercise the AF_ALG socket domain by hashing and encrypting various sized random messages. This exercises the available hashes, ciphers, rng and aead crypto engines in the Linux kernel.

--af-alg-ops N
    stop af-alg workers after N AF_ALG messages are hashed.

--af-alg-dump
    dump the internal list representing cryptographic algorithms parsed from the /proc/crypto file to standard output (stdout).

--aio N
    start N workers that issue multiple small asynchronous I/O writes and reads on a relatively small temporary file using the POSIX aio interface. This will just hit the file system cache and soak up a lot of user and kernel time in issuing and handling I/O requests. By default, each worker process will handle 16 concurrent I/O requests.

--aio-ops N
    stop POSIX asynchronous I/O workers after N bogo asynchronous I/O requests.

--aio-requests N
    specify the number of POSIX asynchronous I/O requests each worker should issue, the default is 16; 1 to 4096 are allowed.

--aiol N
    start N workers that issue multiple 4K random asynchronous I/O writes using the Linux aio system calls io_setup(2), io_submit(2), io_getevents(2) and io_destroy(2). By default, each worker process will handle 16 concurrent I/O requests.

--aiol-ops N
    stop Linux asynchronous I/O workers after N bogo asynchronous I/O requests.

--aiol-requests N
    specify the number of Linux asynchronous I/O requests each worker should issue, the default is 16; 1 to 4096 are allowed.

--alarm N
    start N workers that exercise alarm(2) with MAXINT, 0 and random alarm and sleep delays that get prematurely interrupted. Before each alarm is scheduled any previous pending alarms are cancelled with zero second alarm calls.

--alarm-ops N
    stop after N alarm bogo operations.

--apparmor N
    start N workers that exercise various parts of the AppArmor interface. Currently one needs root permission to run this particular test. Only available on Linux systems with AppArmor support and requires the CAP_MAC_ADMIN capability.

--apparmor-ops
    stop the AppArmor workers after N bogo operations.

--atomic N
    start N workers that exercise various GCC __atomic_*() built in operations on 8, 16, 32 and 64 bit integers that are shared among the N workers. This stressor is only available for builds using GCC 4.7.4 or higher. The stressor forces many front end cache stalls and cache references.

--atomic-ops N
    stop the atomic workers after N bogo atomic operations.

--bad-altstack N
    start N workers that create broken alternative signal stacks for SIGSEGV and SIGBUS handling that in turn create secondary SIGSEGV/SIGBUS errors. A variety of randonly selected nefarious methods are used to create the stacks:

    •   Unmapping the alternative signal stack, before triggering the signal handling.
    •   Changing the alternative signal stack to just being read only, write only, execute only.
    •   Using a NULL alternative signal stack.
    •   Using the signal handler object as the alternative signal stack.
    •   Unmapping the alternative signal stack during execution of the signal handler.
    •   Using a read-only text segment for the alternative signal stack.
    •   Using an undersized alternative signal stack.
    •   Using the VDSO as an alternative signal stack.
    •   Using an alternative stack mapped onto /dev/zero.
    •   Using an alternative stack mapped to a zero sized temporary file to generate a SIGBUS error.

--bad-altstack-ops N
    stop the bad alternative stack stressors after N SIGSEGV bogo operations.

--bad-ioctl N
    start N workers that perform a range of illegal bad read ioctls (using _IOR) across the device drivers. This exercises page size, 64 bit, 32 bit, 16 bit and 8 bit reads as well as NULL addresses, non-readable pages and PROT_NONE mapped pages. Currently only for Linux and requires the --pathological option.

--bad-ioctl-method [ inc | random | random-inc | stride ]
    select the method of changing the ioctl command (number, type) tuple per iteration, the default is random-inc. Available bad-ioctl methods are described as follows:
    Method | Description
    inc | increment ioctl command by 1
    random | use a random ioctl command
    random-inc | increment ioctl command by a random value
    random-stride | increment ioctl command number by 1 and decrement command type by 3

--bad-ioctl-ops N
    stop the bad ioctl stressors after N bogo ioctl operations.

-B N, --bigheap N
    start N workers that grow their heaps by reallocating memory. If the out of memory killer (OOM) on Linux kills the worker or the allocation fails then the allocating process starts all over again. Note that the OOM adjustment for the worker is set so that the OOM killer will treat these workers as the first candidate processes to kill.

--bigheap-ops N
    stop the big heap workers after N bogo allocation operations are completed.

--bigheap-bytes N
    maximum heap growth as N bytes per bigheap worker. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--bigheap-growth N
    specify amount of memory to grow heap by per iteration. Size can be from 4K to 64MB. Default is 64K.

--bigheap-mlock
    attempt to mlock future allocated pages into memory causing more memory pressure. If mlock(MCL_FUTURE) is implemented then this will stop newly allocated pages from being swapped out.

--binderfs N
    start N workers that mount, exercise and unmount binderfs. The binder control device is exercised with 256 sequential BINDER_CTL_ADD ioctl calls per loop.

--binderfs-ops N
    stop after N binderfs cycles.

--bind-mount N
    start N workers that repeatedly bind mount / to / inside a user namespace. This can consume resources rapidly, forcing out of memory situations. Do not use this stressor unless you want to risk hanging your machine.

--bind-mount-ops N
    stop after N bind mount bogo operations.

--branch N
    start N workers that randomly branch to 1024 randomly selected locations and hence exercise the CPU branch prediction logic.

--branch-ops N
    stop the branch stressors after N × 1024 branches

--brk N
    start N workers that grow the data segment by one page at a time using multiple brk(2) calls. Each successfully allocated new page is touched to ensure it is resident in memory. If an out of memory condition occurs then the test will reset the data segment to the point before it started and repeat the data segment resizing over again. The process adjusts the out of memory setting so that it may be killed by the out of memory (OOM) killer before other processes. If it is killed by the OOM killer then it will be automatically re-started by a monitoring parent process.

--brk-ops N
    stop the brk workers after N bogo brk operations.

--brk-bytes N
    maximum brk growth as N bytes per brk worker. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--brk-mlock
    attempt to mlock future brk pages into memory causing more memory pressure. If mlock(MCL_FUTURE) is implemented then this will stop new brk pages from being swapped out.

--brk-notouch
    do not touch each newly allocated data segment page. This disables the default of touching each newly allocated page and hence avoids the kernel from necessarily backing the page with physical memory.

--bsearch N
    start N workers that binary search a sorted array of 32 bit integers using bsearch(3). By default, there are 65536 elements in the array. This is a useful method to exercise random access of memory and processor cache.

--bsearch-ops N
    stop the bsearch worker after N bogo bsearch operations are completed.

--bsearch-size N
    specify the size (number of 32 bit integers) in the array to bsearch. Size can be from 1K to 4M.

-C N, --cache N
    start N workers that perform random wide spread memory read and writes to thrash the CPU cache. The code does not intelligently determine the CPU cache configuration and so it may be sub-optimal in producing hit-miss read/write activity for some processors.

--cache-cldemote
    cache line demote (x86 only). This is a no-op for non-x86 architectures and older x86 processors that do not support this feature.

--cache-clflushopt
    use optimized cache line flush (x86 only). This is a no-op for non-x86 architectures and older x86 processors that do not support this feature.

--cache-clwb
    cache line writeback (x86 only). This is a no-op for non-x86 architectures and older x86 processors that do not support this feature.

--cache-enable-all
    where appropriate exercise the cache using cldemote, clflushopt, fence, flush, sfence and prefetch.

--cache-fence
    force write serialization on each store operation (x86 only). This is a no-op for non-x86 architectures.

--cache-flush
    force flush cache on each store operation (x86 only). This is a no-op for non-x86 architectures.

--cache-level N
    specify level of cache to exercise (1=L1 cache, 2=L2 cache, 3=L3/LLC cache (the default)). If the cache hierarchy cannot be determined, built-in defaults will apply.

--cache-no-affinity
    do not change processor affinity when --cache is in effect.

--cache-sfence
    force write serialization on each store operation using the sfence instruction (x86 only). This is a no-op for non-x86 architectures.

--cache-ops N
    stop cache thrash workers after N bogo cache thrash operations.

--cache-prefetch
    force read prefetch on next read address on architectures that support prefetching.

--cache-ways N
    specify the number of cache ways to exercise. This allows a subset of the overall cache size to be exercised.

--cacheline N
    start N workers that exercise reading and writing individual bytes in a shared buffer that is the size of a cache line. Each stressor has 2 running processes that exercise just two bytes that are next to each other. The intent is to try and trigger cacheline corruption, stalls and misses with shared memory accesses. For an N byte sized cacheline, it is recommended to run N / 2 stressor instances.

--cacheline-ops N
    stop cacheline workers after N loops of the byte exercising in a cacheline.

--cacheline-affinity
    frequently change CPU affinity, spread cacheline processes evenly across all online CPUs to try and maximize lower-level cache activity. Attempts to keep adjacent cachelines being exercised by adjacent CPUs.

--cacheline-method method
    specify a cacheline stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required. Available cacheline stress methods are described as follows:
    Method | Description
    all | iterate over all the below cpu stress methods.
    adjacent | increment a specific byte in a cacheline and read the adjacent byte, check for corruption every 7 increments.
    atomicinc | atomically increment a specific byte in a cacheline and check for corruption every 7 increments.
    bits | write and read back shifted bit patterns into specific byte in a cacheline and check for corruption.
    copy | copy an adjacent byte to a specific byte in a cacheline.
    inc | increment and read back a specific byte in a cacheline and check for corruption every 7 increments.
    mix | perform a mix of increment, left and right rotates a specific byte in a cacheline and check for corruption.
    rdfwd64 | increment a specific byte in a cacheline and then read in forward direction an entire cacheline using 64 bit reads.
    rdints | increment a specific byte in a cacheline and then read data at that byte location in naturally aligned locations integer values of size 8, 16, 32, 64 and 128 bits.
    rdrev64 | increment a specific byte in a cacheline and then read in reverse direction an entire cacheline using 64 bit reads.
    rdwr | read and write the same 8 bit value into a specific byte in a cacheline and check for corruption.

--cap N
    start N workers that read per process capabilities via calls to capget(2) (Linux only).

--cap-ops N
    stop after N cap bogo operations.

--chattr N
    start N workers that attempt to exercise file attributes via the EXT2_IOC_SETFLAGS ioctl. This is intended to be intentionally racy and exercise a range of chattr attributes by enabling and disabling them on a file shared amongst the N chattr stressor processes. (Linux only).

--chattr-ops N
    stop after N chattr bogo operations.

--chdir N
    start N workers that change directory between directories using chdir(2).

--chdir-ops N
    stop after N chdir bogo operations.

--chdir-dirs N
    exercise chdir on N directories. The default is 8192 directories, this allows 64 to 65536 directories to be used instead.

--chmod N
    start N workers that change the file mode bits via chmod(2) and fchmod(2) on the same file. The greater the value for N then the more contention on the single file. The stressor will work through all the combination of mode bits.

--chmod-ops N
    stop after N chmod bogo operations.

--chown N
    start N workers that exercise chown(2) on the same file. The greater the value for N then the more contention on the single file.

--chown-ops N
    stop the chown workers after N bogo chown(2) operations.

--chroot N
    start N workers that exercise chroot(2) on various valid and invalid chroot paths. Only available on Linux systems and requires the CAP_SYS_ADMIN capability.

--chroot-ops N
    stop the chroot workers after N bogo chroot(2) operations.

--clock N
    start N workers exercising clocks and POSIX timers. For all known clock types this will exercise clock_getres(2), clock_gettime(2) and clock_nanosleep(2). For all known timers it will create a random duration timer and busy poll this until it expires. This stressor will cause frequent context switching.

--clock-ops N
    stop clock stress workers after N bogo operations.

--clone N
    start N workers that create clones (via the clone(2) and clone3() system calls). This will rapidly try to create a default of 8192 clones that immediately die and wait in a zombie state until they are reaped. Once the maximum number of clones is reached (or clone fails because one has reached the maximum allowed) the oldest clone thread is reaped and a new clone is then created in a first-in first-out manner, and then repeated. A random clone flag is selected for each clone to try to exercise different clone operations. The clone stressor is a Linux only option.

--clone-ops N
    stop clone stress workers after N bogo clone operations.

--clone-max N
    try to create as many as N clone threads. This may not be reached if the system limit is less than N.

--close N
    start N workers that try to force race conditions on closing opened file descriptors. These file descriptors have been opened in various ways to try and exercise different kernel close handlers.

--close-ops N
    stop close workers after N bogo close operations.

--context N
    start N workers that run three threads that use swapcontext(3) to implement the thread-to-thread context switching. This exercises rapid process context saving and restoring and is bandwidth limited by register and memory save and restore rates.

--context-ops N
    stop context workers after N bogo context switches. In this stressor, 1 bogo op is equivalent to 1000 swapcontext calls.

--copy-file N
    start N stressors that copy a file using the Linux copy_file_range(2) system call. 128 KB chunks of data are copied from random locations from one file to random locations to a destination file. By default, the files are 256 MB in size. Data is sync'd to the filesystem after each copy_file_range(2) call.

--copy-file-ops N
    stop after N copy_file_range() calls.

--copy-file-bytes N
    copy file size, the default is 256 MB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

-c N, --cpu N
    start N workers exercising the CPU by sequentially working through all the different CPU stress methods. Instead of exercising all the CPU stress methods, one can specify a specific CPU stress method with the --cpu-method option.

--cpu-ops N
    stop cpu stress workers after N bogo operations.

-l P, --cpu-load P
    load CPU with P percent loading for the CPU stress workers. 0 is effectively a sleep (no load) and 100 is full loading. The loading loop is broken into compute time (load%) and sleep time (100% - load%). Accuracy depends on the overall load of the processor and the responsiveness of the scheduler, so the actual load may be different from the desired load. Note that the number of bogo CPU operations may not be linearly scaled with the load as some systems employ CPU frequency scaling and so heavier loads produce an increased CPU frequency and greater CPU bogo operations. Note: This option only applies to the --cpu stressor option and not to all of the cpu class of stressors.

--cpu-load-slice S
    note - this option is only useful when --cpu-load is less than 100%. The CPU load is broken into multiple busy and idle cycles. Use this option to specify the duration of a busy time slice. A negative value for S specifies the number of iterations to run before idling the CPU (e.g. -30 invokes 30 iterations of a CPU stress loop). A zero value selects a random busy time between 0 and 0.5 seconds. A positive value for S specifies the number of milliseconds to run before idling the CPU (e.g. 100 keeps the CPU busy for 0.1 seconds). Specifying small values for S lends to small time slices and smoother scheduling. Setting --cpu-load as a relatively low value and --cpu-load-slice to be large will cycle the CPU between long idle and busy cycles and exercise different CPU frequencies. The thermal range of the CPU is also cycled, so this is a good mechanism to exercise the scheduler, frequency scaling and passive/active thermal cooling mechanisms. Note: This option only applies to the --cpu stressor option and not to all of the cpu class of stressors.

--cpu-old-metrics
    as of version V0.14.02 the cpu stressor now normalizes each of the cpu stressor method bogo-op counters to try and ensure a similar bogo-op rate for all the methods to avoid the shorter running (and faster) methods from skewing the bogo-op rates when using the default "all" method. This is based on a reference Intel i5-8350U processor and hence the bogo-ops normalizing factors will be skew somewhat on different CPUs, but so significantly as the original bogo-op counter rates. To disable the normalization and fall back to the original metrics, use this option.

--cpu-method method
    specify a cpu stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required. Available cpu stress methods are described as follows:
    Method | Description
    all | iterate over all the below cpu stress methods
    ackermann | Ackermann function: compute A(3, 7), where: A(m, n) = n + 1 if m = 0; A(m - 1, 1) if m > 0 and n = 0; A(m - 1, A(m, n - 1)) if m > 0 and n > 0
    apery | calculate Apery's constant ζ(3); the sum of 1/(n ↑ 3) to a precision of 1.0x10↑14
    bitops | various bit operations from bithack, namely: reverse bits, parity check, bit count, round to nearest power of 2
    callfunc | recursively call 8 argument C function to a depth of 1024 calls and unwind
    cfloat | 1000 iterations of a mix of floating point complex operations
    cdouble | 1000 iterations of a mix of double floating point complex operations
    clongdouble | 1000 iterations of a mix of long double floating point complex operations
    collatz | compute the 1348 steps in the collatz sequence starting from number 989345275647. Where f(n) = n / 2 (for even n) and f(n) = 3n + 1 (for odd n).
    correlate | perform a 8192 × 512 correlation of random doubles
    crc16 | compute 1024 rounds of CCITT CRC16 on random data
    decimal32 | 1000 iterations of a mix of 32 bit decimal floating point operations (GCC only)
    decimal64 | 1000 iterations of a mix of 64 bit decimal floating point operations (GCC only)
    decimal128 | 1000 iterations of a mix of 128 bit decimal floating point operations (GCC only)
    dither | Floyd-Steinberg dithering of a 1024 × 768 random image from 8 bits down to 1 bit of depth
    div8 | 50,000 8 bit unsigned integer divisions
    div16 | 50,000 16 bit unsigned integer divisions
    div32 | 50,000 32 bit unsigned integer divisions
    div64 | 50,000 64 bit unsigned integer divisions
    div128 | 50,000 128 bit unsigned integer divisions
    double | 1000 iterations of a mix of double precision floating point operations
    euler | compute e using n (1 + (1 ÷ n)) ↑ n
    explog | iterate on n exp(log(n) ÷ 1.00002)
    factorial | find factorials from 1..150 using Stirling's and Ramanujan's approximations
    fibonacci | compute Fibonacci sequence of 0, 1, 1, 2, 5, 8...
    fft | 4096 sample Fast Fourier Transform
    fletcher16 | 1024 rounds of a naïve implementation of a 16 bit Fletcher's checksum
    float | 1000 iterations of a mix of floating point operations
    float16 | 1000 iterations of a mix of 16 bit floating point operations
    float32 | 1000 iterations of a mix of 32 bit floating point operations
    float64 | 1000 iterations of a mix of 64 bit floating point operations
    float80 | 1000 iterations of a mix of 80 bit floating point operations
    float128 | 1000 iterations of a mix of 128 bit floating point operations
    floatconversion | perform 65536 iterations of floating point conversions between float, double and long double floating point variables.
    gamma | calculate the Euler-Mascheroni constant γ using the limiting difference between the harmonic series (1 + 1/2 + 1/3 + 1/4 + 1/5 ... + 1/n) and the natural logarithm ln(n), for n = 80000.
    gcd | compute GCD of integers
    gray | calculate binary to gray code and gray code back to binary for integers from 0 to 65535
    hamming | compute Hamming H(8,4) codes on 262144 lots of 4 bit data. This turns 4 bit data into 8 bit Hamming code containing 4 parity bits. For data bits d1..d4, parity bits are computed as: p1 = d2 + d3 + d4 p2 = d1 + d3 + d4 p3 = d1 + d2 + d4 p4 = d1 + d2 + d3
    hanoi | solve a 21 disc Towers of Hanoi stack using the recursive solution
    hyperbolic | compute sinh(θ) × cosh(θ) + sinh(2θ) + cosh(3θ) for float, double and long double hyperbolic sine and cosine functions where θ = 0 to 2π in 1500 steps
    idct | 8 × 8 IDCT (Inverse Discrete Cosine Transform).
    int8 | 1000 iterations of a mix of 8 bit integer operations.
    int16 | 1000 iterations of a mix of 16 bit integer operations.
    int32 | 1000 iterations of a mix of 32 bit integer operations.
    int64 | 1000 iterations of a mix of 64 bit integer operations.
    int128 | 1000 iterations of a mix of 128 bit integer operations (GCC only).
    int32float | 1000 iterations of a mix of 32 bit integer and floating point operations.
    int32double | 1000 iterations of a mix of 32 bit integer and double precision floating point operations.
    int32longdouble | 1000 iterations of a mix of 32 bit integer and long double precision floating point operations.
    int64float | 1000 iterations of a mix of 64 bit integer and floating point operations.
    int64double | 1000 iterations of a mix of 64 bit integer and double precision floating point operations.
    int64longdouble | 1000 iterations of a mix of 64 bit integer and long double precision floating point operations.
    int128float | 1000 iterations of a mix of 128 bit integer and floating point operations (GCC only).
    int128double | 1000 iterations of a mix of 128 bit integer and double precision floating point operations (GCC only).
    int128longdouble | 1000 iterations of a mix of 128 bit integer and long double precision floating point operations (GCC only).
    int128decimal32 | 1000 iterations of a mix of 128 bit integer and 32 bit decimal floating point operations (GCC only).
    int128decimal64 | 1000 iterations of a mix of 128 bit integer and 64 bit decimal floating point operations (GCC only).
    int128decimal128 | 1000 iterations of a mix of 128 bit integer and 128 bit decimal floating point operations (GCC only).
    intconversion | perform 65536 iterations of integer conversions between int16, int32 and int64 variables.
    ipv4checksum | compute 1024 rounds of the 16 bit ones' complement IPv4 checksum.
    jmp | Simple unoptimised compare >, <, == and jmp branching.
    lfsr32 | 16384 iterations of a 32 bit Galois linear feedback shift register using the polynomial x↑32 + x↑31 + x↑29 + x + 1. This generates a ring of 2↑32 - 1 unique values (all 32 bit values except for 0).
    ln2 | compute ln(2) based on series: 1 - 1/2 + 1/3 - 1/4 + 1/5 - 1/6 ...
    logmap | 16384 iterations computing chaotic double precision values using the logistic map Χn+1 = r × Χn × (1 - Χn) where r > ≈ 3.56994567
    longdouble | 1000 iterations of a mix of long double precision floating point operations.
    loop | simple empty loop.
    matrixprod | matrix product of two 128 × 128 matrices of double floats. Testing on 64 bit x86 hardware shows that this is provides a good mix of memory, cache and floating point operations and is probably the best CPU method to use to make a CPU run hot.
    nsqrt | compute sqrt() of long doubles using Newton-Raphson.
    omega | compute the omega constant defined by Ωe↑Ω = 1 using efficient iteration of Ωn+1 = (1 + Ωn) / (1 + e↑Ωn).
    parity | compute parity using various methods from the Standford Bit Twiddling Hacks. Methods employed are: the naïve way, the naïve way with the Brian Kernigan bit counting optimisation, the multiply way, the parallel way, the lookup table ways (2 variations) and using the __builtin_parity function.
    phi | compute the Golden Ratio φ using series.
    pi | compute π using the Srinivasa Ramanujan fast convergence algorithm.
    prime | find the first 10000 prime numbers using a slightly optimised brute force naïve trial division search.
    psi | compute ψ (the reciprocal Fibonacci constant) using the sum of the reciprocals of the Fibonacci numbers.
    queens | compute all the solutions of the classic 8 queens problem for board sizes 1..11.
    rand | 16384 iterations of rand(), where rand is the MWC pseudo random number generator. The MWC random function concatenates two 16 bit multiply-with-carry generators: x(n) = 36969 × x(n - 1) + carry, y(n) = 18000 × y(n - 1) + carry mod 2 ↑ 16 and has period of around 2 ↑ 60.
    rand48 | 16384 iterations of drand48(3) and lrand48(3).
    rgb | convert RGB to YUV and back to RGB (CCIR 601).
    sieve | find the first 10000 prime numbers using the sieve of Eratosthenes.
    stats | calculate minimum, maximum, arithmetic mean, geometric mean, harmoninc mean and standard deviation on 250 randomly generated positive double precision values.
    sqrt | compute sqrt(rand()), where rand is the MWC pseudo random number generator.
    trig | compute sin(θ) × cos(θ) + sin(2θ) + cos(3θ) for float, double and long double sine and cosine functions where θ = 0 to 2π in 1500 steps.
    union | perform integer arithmetic on a mix of bit fields in a C union. This exercises how well the compiler and CPU can perform integer bit field loads and stores.
    zeta | compute the Riemann Zeta function ζ(s) for s = 2.0..10.0

    Note that some of these methods try to exercise the CPU with computations found in some real world use cases. However, the code has not been optimised on a per-architecture basis, so may be a sub-optimal compared to hand-optimised code used in some applications. They do try to represent the typical instruction mixes found in these use cases.

--cpu-online N
    start N workers that put randomly selected CPUs offline and online. This Linux only stressor requires root privilege to perform this action. By default the first CPU (CPU 0) is never offlined as this has been found to be problematic on some systems and can result in a shutdown.

--cpu-online-all
    The default is to never offline the first CPU. This option will offline and online all the CPUs including CPU 0. This may cause some systems to shutdown.

--cpu-online-ops N
    stop after offline/online operations.

--crypt N
    start N workers that encrypt a 16 character random password using crypt(3). The password is encrypted using MD5, SHA-256 and SHA-512 encryption methods.

--crypt-ops N
    stop after N bogo encryption operations.

--cyclic N
    start N workers that exercise the real time FIFO or Round Robin schedulers with cyclic nanosecond sleeps. Normally one would just use 1 worker instance with this stressor to get reliable statistics. By default this stressor measures the first 10 thousand latencies and calculates the mean, mode, minimum, maximum latencies along with various latency percentiles for the just the first cyclic stressor instance. One has to run this stressor with CAP_SYS_NICE capability to enable the real time scheduling policies. The FIFO scheduling policy is the default.

--cyclic-ops N
    stop after N sleeps.

--cyclic-dist N
    calculate and print a latency distribution with the interval of N nanoseconds. This is helpful to see where the latencies are clustering.

--cyclic-method [ clock_ns | itimer | poll | posix_ns | pselect | usleep ]
    specify the cyclic method to be used, the default is clock_ns. The available cyclic methods are as follows:
    Method | Description
    clock_ns | sleep for the specified time using the clock_nanosleep(2) high resolution nanosleep and the CLOCK_REALTIME real time clock.
    itimer | wakeup a paused process with a CLOCK_REALTIME itimer signal.
    poll | delay for the specified time using a poll delay loop that checks for time changes using clock_gettime(2) on the CLOCK_REALTIME clock.
    posix_ns | sleep for the specified time using the POSIX nanosleep(2) high resolution nanosleep.
    pselect | sleep for the specified time using pselect(2) with null file descriptors.
    usleep | sleep to the nearest microsecond using usleep(2).

--cyclic-policy [ fifo | rr ]
    specify the desired real time scheduling policy, ff (first-in, first-out) or rr (round-robin).

--cyclic-prio P
    specify the scheduling priority P. Range from 1 (lowest) to 100 (highest).

--cyclic-samples N
    measure N samples. Range from 1 to 100000000 samples.

--cyclic-sleep N
    sleep for N nanoseconds per test cycle using clock_nanosleep(2) with the CLOCK_REALTIME timer. Range from 1 to 1000000000 nanoseconds.

--daemon N
    start N workers that each create a daemon that dies immediately after creating another daemon and so on. This effectively works through the process table with short lived processes that do not have a parent and are waited for by init. This puts pressure on init to do rapid child reaping. The daemon processes perform the usual mix of calls to turn into typical UNIX daemons, so this artificially mimics very heavy daemon system stress.

--daemon-ops N
    stop daemon workers after N daemons have been created.

--daemon-wait
    wait for daemon child processes rather than let init handle the waiting. Enabling this option will reduce the daemon fork rate because of the synchronous wait delays.

--dccp N
    start N workers that send and receive data using the Datagram Congestion Control Protocol (DCCP) (RFC4340). This involves a pair of client/server processes performing rapid connect, send and receives and disconnects on the local host.

--dccp-domain D
    specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are supported.

--dccp-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--dccp-port P
    start DCCP at port P. For N dccp worker processes, ports P to P - 1 are used.

--dccp-ops N
    stop dccp stress workers after N bogo operations.

--dccp-opts [ send | sendmsg | sendmmsg ]
    by default, messages are sent using send(2). This option allows one to specify the sending method using send(2), sendmsg(2) or sendmmsg(2). Note that sendmmsg is only available for Linux systems that support this system call.

--dekker N
    start N workers that exercises mutex exclusion between two processes using shared memory with the Dekker Algorithm. Where possible this uses memory fencing and falls back to using GCC __sync_synchronize if they are not available. The stressors contain simple mutex and memory coherency sanity checks.

--dekker-ops N
    stop dekker workers after N mutex operations.

-D N, --dentry N
    start N workers that create and remove directory entries. This should create file system meta data activity. The directory entry names are suffixed by a gray-code encoded number to try to mix up the hashing of the namespace.

--dentry-ops N
    stop denty thrash workers after N bogo dentry operations.

--dentry-order [ forward | reverse | stride | random ]
    specify unlink order of dentries, can be one of forward, reverse, stride or random. By default, dentries are unlinked in random order. The forward order will unlink them from first to last, reverse order will unlink them from last to first, stride order will unlink them by stepping around order in a quasi-random pattern and random order will randomly select one of forward, reverse or stride orders.

--dentries N
    create N dentries per dentry thrashing loop, default is 2048.

--dev N
    start N workers that exercise the /dev devices. Each worker runs 5 concurrent threads that perform open(2), fstat(2), lseek(2), poll(2), fcntl(2), mmap(2), munmap(2), fsync(2) and close(2) on each device. Note that watchdog devices are not exercised.

--dev-ops N
    stop dev workers after N bogo device exercising operations.

--dev-file filename
    specify the device file to exercise, for example, /dev/null. By default the stressor will work through all the device files it can fine, however, this option allows a single device file to be exercised.

--dev-shm N
    start N workers that fallocate large files in /dev/shm and then mmap these into memory and touch all the pages. This exercises pages being moved to/from the buffer cache. Linux only.

--dev-shm-ops N
    stop after N bogo allocation and mmap /dev/shm operations.

--dir N
    start N workers that create and remove directories using mkdir and rmdir.

--dir-ops N
    stop directory thrash workers after N bogo directory operations.

--dir-dirs N
    exercise dir on N directories. The default is 8192 directories, this allows 64 to 65536 directories to be used instead.

--dirdeep N
    start N workers that create a depth-first tree of directories to a maximum depth as limited by PATH_MAX or ENAMETOOLONG (which ever occurs first). By default, each level of the tree contains one directory, but this can be increased to a maximum of 10 sub-trees using the --dirdeep-dir option. To stress inode creation, a symlink and a hardlink to a file at the root of the tree is created in each level.

--dirdeep-ops N
    stop directory depth workers after N bogo directory operations.

--dirdeep-bytes N
    allocated file size, the default is 0. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Used in conjunction with the --dirdeep-files option.

--dirdeep-dirs N
    create N directories at each tree level. The default is just 1 but can be increased to a maximum of 36 per level.

--dirdeep-files N
    create N files at each tree level. The default is 0 with the file size specified by the --dirdeep-bytes option.

--dirdeep-inodes N
    consume up to N inodes per dirdeep stressor while creating directories and links. The value N can be the number of inodes or a percentage of the total available free inodes on the filesystem being used.

--dirmany N
    start N stressors that create as many files in a directory as possible and then remove them. The file creation phase stops when an error occurs (for example, out of inodes, too many files, quota reached, etc.) and then the files are removed. This cycles until the run time is reached or the file creation count bogo-ops metric is reached. This is a much faster and light weight directory exercising stressor compared to the dentry stressor.

--dirmany-ops N
    stop dirmany stressors after N empty files have been created.

--dirmany-bytes N
    allocated file size, the default is 0. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--dnotify N
    start N workers performing file system activities such as making/deleting files/directories, renaming files, etc. to stress exercise the various dnotify events (Linux only).

--dnotify-ops N
    stop inotify stress workers after N dnotify bogo operations.

--dup N
    start N workers that perform dup(2) and then close(2) operations on /dev/zero. The maximum opens at one time is system defined, so the test will run up to this maximum, or 65536 open file descriptors, which ever comes first.

--dup-ops N
    stop the dup stress workers after N bogo open operations.

--dynlib N
    start N workers that dynamically load and unload various shared libraries. This exercises memory mapping and dynamic code loading and symbol lookups. See dlopen(3) for more details of this mechanism.

--dynlib-ops N
    stop workers after N bogo load/unload cycles.

--eigen N
    start N workers that exercise the Eigen C++ matrix library for 2D matrix addition, multiplication, determinant, inverse and transpose operations. on long double, double and float matrices. This currently is only available for gcc/g++ builds.

--eigen-ops N
    stop after N Eigen matrix computations

--eigen-size N
    specify the 2D matrix size N × N. The default is a 32 × 32 matrix.

--eigen-method M
    select the floating point method to use, available methods are:
    Method | Description
    all | iterate over all the Eigen 2D matrix operations
    add-longdouble | addition of two matrices of long double floating point values T{ add-doublee T{ addition of two matrices of double floating point values
    add-float | addition of two matrices of floating point values
    determinant-longdouble | determinant of matrix of long double floating point values
    determinant-double | determinant of matrix of double floating point values
    determinant-float | determinant of matrix of floating point values
    inverse-longdouble | inverse of matrix of long double floating point values
    inverse-double | inverse of matrix of double floating point values
    inverse-float | inverse of matrix of floating point values
    multiply-longdouble | mutiplication of two matrices of long double floating point values
    multiply-doublee | mutiplication of two matrices of double floating point values
    multiply-float | mutiplication of two matrices of floating point values
    transpose-longdouble | transpose of matrix of long double floating point values
    transpose-double | transpose of matrix of double floating point values
    transpose-float | transpose of matrix of floating point values

--efivar N
    start N workers that exercise the Linux /sys/firmware/efi/efivars and /sys/firmware/efi/vars interfaces by reading the EFI variables. This is a Linux only stress test for platforms that support the EFI vars interface and may require the CAP_SYS_ADMIN capability.

--efivar-ops N
    stop the efivar stressors after N EFI variable read operations.

--enosys N
    start N workers that exercise non-functional system call numbers. This calls a wide range of system call numbers to see if it can break a system where these are not wired up correctly. It also keeps track of system calls that exist (ones that don't return ENOSYS) so that it can focus on purely finding and exercising non-functional system calls. This stressor exercises system calls from 0 to __NR_syscalls + 1024, random system calls within constrained in the ranges of 0 to 2↑8, 2↑16, 2↑24, 2↑32, 2↑40, 2↑48, 2↑56 and 2↑64 bits, high system call numbers and various other bit patterns to try to get wide coverage. To keep the environment clean, each system call being tested runs in a child process with reduced capabilities.

--enosys-ops N
    stop after N bogo enosys system call attempts

--env N
    start N workers that creates numerous large environment variables to try to trigger out of memory conditions using setenv(3). If ENOMEM occurs then the environment is emptied and another memory filling retry occurs. The process is restarted if it is killed by the Out Of Memory (OOM) killer.

--env-ops N
    stop after N bogo setenv/unsetenv attempts.

--epoll N
    start N workers that perform various related socket stress activity using epoll_wait(2) to monitor and handle new connections. This involves client/server processes performing rapid connect, send/receives and disconnects on the local host. Using epoll allows a large number of connections to be efficiently handled, however, this can lead to the connection table filling up and blocking further socket connections, hence impacting on the epoll bogo op stats. For ipv4 and ipv6 domains, multiple servers are spawned on multiple ports. The epoll stressor is for Linux only.

--epoll-domain D
    specify the domain to use, the default is unix (aka local). Currently ipv4, ipv6 and unix are supported.

--epoll-port P
    start at socket port P. For N epoll worker processes, ports P to (P * 4) - 1 are used for ipv4, ipv6 domains and ports P to P - 1 are used for the unix domain.

--epoll-ops N
    stop epoll workers after N bogo operations.

--epoll-sockets N
    specify the maximum number of concurrently open sockets allowed in server. Setting a high value impacts on memory usage and may trigger out of memory conditions.

--eventfd N
    start N parent and child worker processes that read and write 8 byte event messages between them via the eventfd mechanism (Linux only).

--eventfd-ops N
    stop eventfd workers after N bogo operations.

--eventfd-nonblock
    enable EFD_NONBLOCK to allow non-blocking on the event file descriptor. This will cause reads and writes to return with EAGAIN rather the blocking and hence causing a high rate of polling I/O.

--exec N
    start N workers continually forking children that exec stress-ng and then exit almost immediately. If a system has pthread support then 1 in 4 of the exec's will be from inside a pthread to exercise exec'ing from inside a pthread context.

--exec-ops N
    stop exec stress workers after N bogo operations.

--exec-fork-method [ clone | fork | rfork | spawn | vfork ]
    select the process creation method using clone(2), fork(2), BSD rfork(2), posix_spawn(3) or vfork(2). Note that vfork will only exec programs using execve due to the constraints on the shared stack between the parent and the child process.

--exec-max P
    create P child processes that exec stress-ng and then wait for them to exit per iteration. The default is 4096; higher values may create many temporary zombie processes that are waiting to be reaped. One can potentially fill up the process table using high values for --exec-max and --exec.

--exec-method [ all | execve | execveat ]
    select the exec system call to use; all will perform a random choice between execve(2) and execveat(2), execve will use execve(2) and execveat will use execveat(2) if it is available.

--exec-no-pthread
    do not use pthread_create(3).

--exit-group N
    start N workers that create 16 pthreads and terminate the pthreads and the controlling child process using exit_group(2). (Linux only stressor).

--exit-group-ops N
    stop after N iterations of pthread creation and deletion loops.

-F N, --fallocate N
    start N workers continually fallocating (preallocating file space) and ftruncating (file truncating) temporary files. If the file is larger than the free space, fallocate will produce an ENOSPC error which is ignored by this stressor.

--fallocate-bytes N
    allocated file size, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--fallocate-ops N
    stop fallocate stress workers after N bogo fallocate operations.

--fanotify N
    start N workers performing file system activities such as creating, opening, writing, reading and unlinking files to exercise the fanotify event monitoring interface (Linux only). Each stressor runs a child process to generate file events and a parent process to read file events using fanotify. Has to be run with CAP_SYS_ADMIN capability.

--fanotify-ops N
    stop fanotify stress workers after N bogo fanotify events.

--far-branch N
    start N workers that exercise calls to tens of thousands of functions that are relatively far from the caller. All functions are 1 op instructions that return to the caller. The functions are placed in pages that are memory mapped with a wide spread of fixed virtual addresses. Function calls are pre-shuffled to create a randomized mix of addresses to call. This stresses the instruction cache and any instruction TLBs.

--far-branch-ops N
    stop after N far branch bogo-ops. One full cycle of calling all the tens of thousands of functions equates to one bogo-op.

--far-branch-pages N
    specify the number of pages to allocate for far branch functions. The number for functions per page depends on the processor architecture, for example, x86 will have 4096 x 1 byte return instructions per 4K page, where as SPARC64 will have only 512 x 8 byte return instructions per 4K page.

--fault N
    start N workers that generates minor and major page faults.

--fault-ops N
    stop the page fault workers after N bogo page fault operations.

--fcntl N
    start N workers that perform fcntl(2) calls with various commands. The exercised commands (if available) are: F_DUPFD, F_DUPFD_CLOEXEC, F_GETFD, F_SETFD, F_GETFL, F_SETFL, F_GETOWN, F_SETOWN, F_GETOWN_EX, F_SETOWN_EX, F_GETSIG, F_SETSIG, F_GETLK, F_SETLK, F_SETLKW, F_OFD_GETLK, F_OFD_SETLK and F_OFD_SETLKW.

--fcntl-ops N
    stop the fcntl workers after N bogo fcntl operations.

--fiemap N
    start N workers that each create a file with many randomly changing extents and has 4 child processes per worker that gather the extent information using the FS_IOC_FIEMAP ioctl(2).

--fiemap-ops N
    stop after N fiemap bogo operations.

--fiemap-bytes N
    specify the size of the fiemap'd file in bytes. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Larger files will contain more extents, causing more stress when gathering extent information.

--fifo N
    start N workers that exercise a named pipe by transmitting 64 bit integers.

--fifo-data-size N
    set the byte size of the fifo write/reads, default is 8, range 8..4096.

--fifo-ops N
    stop fifo workers after N bogo pipe write operations.

--fifo-readers N
    for each worker, create N fifo reader workers that read the named pipe using simple blocking reads. Default is 4, range 1..64.

--file-ioctl N
    start N workers that exercise various file specific ioctl(2) calls. This will attempt to use the FIONBIO, FIOQSIZE, FIGETBSZ, FIOCLEX, FIONCLEX, FIONBIO, FIOASYNC, FIOQSIZE, FIFREEZE, FITHAW, FICLONE, FICLONERANGE, FIONREAD, FIONWRITE and FS_IOC_RESVSP ioctls if these are defined.

--file-ioctl-ops N
    stop file-ioctl workers after N file ioctl bogo operations.

--filename N
    start N workers that exercise file creation using various length filenames containing a range of allowed filename characters. This will try to see if it can exceed the file system allowed filename length was well as test various filename lengths between 1 and the maximum allowed by the file system.

--filename-ops N
    stop filename workers after N bogo filename tests.

--filename-opts opt
    use characters in the filename based on option 'opt'. Valid options are:
    Option | Description
    probe | default option, probe the file system for valid allowed characters in a file name and use these
    posix | use characters as specified by The Open Group Base Specifications Issue 7, POSIX.1-2008, 3.278 Portable Filename Character Set
    ext | use characters allowed by the ext2, ext3, ext4 file systems, namely any 8 bit character apart from NUL and /

--flock N
    start N workers locking on a single file.

--flock-ops N
    stop flock stress workers after N bogo flock operations.

--flush-cache N
    start N workers that flush the data and instruction cache (where possible). Some architectures may not support cache flushing on either cache, in which case these become no-ops.

--flush-cache-ops N
    stop after N cache flush iterations.

--fma N
    start N workers that exercise single and double precision floating point multiplication and add operations on arrays of 512 floating point values. More modern processors (Intel Haswell, AMD Bulldozer and Piledriver) and modern C compilers these will be performed by fused-multiply-add (fma3) opcodes. Operations used are:
    a a × b + c
    a b × a + c
    a b × c + a

--fma-ops N
    stop after N bogo-loops of the 3 above operations on 512 single and double precision floating point numbers.

-f N, --fork N
    start N workers continually forking children that immediately exit.

--fork-ops N
    stop fork stress workers after N bogo operations.

--fork-max P
    create P child processes and then wait for them to exit per iteration. The default is just 1; higher values will create many temporary zombie processes that are waiting to be reaped. One can potentially fill up the process table using high values for --fork-max and --fork.

--fork-vm
    enable detrimental performance virtual memory advice using madvise on all pages of the forked process. Where possible this will try to set every page in the new process with using madvise MADV_MERGEABLE, MADV_WILLNEED, MADV_HUGEPAGE and MADV_RANDOM flags. Linux only.

--forkheavy N
    start N workers that fork child processes from a parent that has thousands of allocated system resources. The fork becomes a heavyweight operations as it has to duplicate the resource references of the parent. Each stressor instance creates and reaps up to 4096 child processes that are created and reaped in a first-in first-out manner.

--forkheavy-allocs N
    attempt N resource allocation loops per stressor instance. Resources include pipes, file descriptors, memory mappings, pthreads, timers, ptys, semaphores, message queues and temporary files. These create heavyweight processes that are more time expensive to fork from. Default is 16384.

--forkheavy-mlock
    attempt to mlock future allocated pages into memory causing more memory pressure. If mlock(MCL_FUTURE) is implemented then this will stop new brk pages from being swapped out.

--forkheavy-ops N
    stop after N fork calls.

--forkheavy-procs N
    attempt to fork N processes per stressor. The default is 4096 processes.

--fp N
    start N workers that exercise addition, multiplication and division operations on a range of floating point types. For each type, 8 floating point values are operated upon 65536 times in a loop per bogo op.

--fp-ops N
    stop after N floating point bogo ops. Note that bogo-ops are counted for just standard float, double and long double floating point types.

--fp-method method
    select the floating point method to use, available methods are:
    Method | Description
    all | iterate over all the following floating point methods:
    float128add | 128 bit floating point add
    float80add | 80 bit floating point add
    float64add | 64 bit floating point add
    float32add | 32 bit binary32 floating point add
    floatadd | floating point add
    doubleadd | double precision floating point add
    ldoubleadd | long double precision floating point add
    float128mul | 128 bit floating point multiply
    float80mul | 80 bit floating point multiply
    float64mul | 64 bit floating point multiply
    float32mul | 32 bit binary32 floating point multiply
    floatmul | floating point multiply
    doublemul | double precision floating point multiply
    ldoublemul | long double precision floating point multiply
    float128div | 128 bit floating point divide
    float80div | 80 bit floating point divide
    float64div | 64 bit floating point divide
    float32div | 32 bit binary32 floating point divide
    floatdiv | floating point divide
    doublediv | double precision floating point divide
    ldoublediv | long double precision floating point divide

    Note that some of these floating point methods may not be available on some systems.

--fp-error N
    start N workers that generate floating point exceptions. Computations are performed to force and check for the FE_DIVBYZERO, FE_INEXACT, FE_INVALID, FE_OVERFLOW and FE_UNDERFLOW exceptions. EDOM and ERANGE errors are also checked.

--fp-error-ops N
    stop after N bogo floating point exceptions.

--fpunch N
    start N workers that punch and fill holes in a 16 MB file using five concurrent processes per stressor exercising on the same file. Where available, this uses fallocate(2) FALLOC_FL_KEEP_SIZE, FALLOC_FL_PUNCH_HOLE, FALLOC_FL_ZERO_RANGE, FALLOC_FL_COLLAPSE_RANGE and FALLOC_FL_INSERT_RANGE to make and fill holes across the file and breaks it into multiple extents.

--fpunch-ops N
    stop fpunch workers after N punch and fill bogo operations.

--fsize N
    start N workers that exercise file size limits (via setrlimit RLIMIT_FSIZE) with file sizes that are fixed, random and powers of 2. The files are truncated and allocated to trigger SIGXFSZ signals.

--fsize-ops N
    stop after N bogo file size test iterations.

--fstat N
    start N workers fstat'ing files in a directory (default is /dev).

--fstat-ops N
    stop fstat stress workers after N bogo fstat operations.

--fstat-dir directory
    specify the directory to fstat to override the default of /dev. All the files in the directory will be fstat'd repeatedly.

--full N
    start N workers that exercise /dev/full. This attempts to write to the device (which should always get error ENOSPC), to read from the device (which should always return a buffer of zeros) and to seek randomly on the device (which should always succeed). (Linux only).

--full-ops N
    stop the stress full workers after N bogo I/O operations.

--funccall N
    start N workers that call functions of 1 through to 9 arguments. By default all functions with a range of argument types are called, however, this can be changed using the --funccall-method option. This exercises stack function argument passing and re-ordering on the stack and in registers.

--funccall-ops N
    stop the funccall workers after N bogo function call operations. Each bogo operation is 1000 calls of functions of 1 through to 9 arguments of the chosen argument type.

--funccall-method method
    specify the method of funccall argument type to be used. The default is all the types but can be one of bool, uint8, uint16, uint32, uint64, uint128, float, double, longdouble, cfloat (complex float), cdouble (complex double), clongdouble (complex long double), float16, float32, float64, float80, float128, decimal32, decimal64 and decimal128. Note that some of these types are only available with specific architectures and compiler versions.

--funcret N
    start N workers that pass and return by value various small to large data types.

--funcret-ops N
    stop the funcret workers after N bogo function call operations.

--funcret-method method
    specify the method of funcret argument type to be used. The default is uint64_t but can be one of uint8 uint16 uint32 uint64 uint128 float double longdouble float80 float128 decimal32 decimal64 decimal128 uint8x32 uint8x128 uint64x128.

--futex N
    start N workers that rapidly exercise the futex system call. Each worker has two processes, a futex waiter and a futex waker. The waiter waits with a very small timeout to stress the timeout and rapid polled futex waiting. This is a Linux specific stress option.

--futex-ops N
    stop futex workers after N bogo successful futex wait operations.

--get N
    start N workers that call system calls that fetch data from the kernel, currently these are: getpid, getppid, getcwd, getgid, getegid, getuid, getgroups, getpgrp, getpgid, getpriority, getresgid, getresuid, getrlimit, prlimit, getrusage, getsid, gettid, getcpu, gettimeofday, uname, adjtimex, sysfs. Some of these system calls are OS specific.

--get-ops N
    stop get workers after N bogo get operations.

--getdent N
    start N workers that recursively read directories /proc, /dev/, /tmp, /sys and /run using getdents and getdents64 (Linux only).

--getdent-ops N
    stop getdent workers after N bogo getdent bogo operations.

--getrandom N
    start N workers that get 8192 random bytes from the /dev/urandom pool using the getrandom(2) system call (Linux) or getentropy(2) (OpenBSD).

--getrandom-ops N
    stop getrandom workers after N bogo get operations.

--goto N
    start N workers that perform 1024 forward branches (to next instruction) or backward branches (to previous instruction) for each bogo operation loop. By default, every 1024 branches the direction is randomly chosen to be forward or backward. This stressor exercises suboptimal pipelined execution and branch prediction logic.

--goto-ops N
    stop goto workers after N bogo loops of 1024 branch instructions.

--goto-direction [ forward | backward | random ]
    select the branching direction in the stressor loop, forward for forward only branching, backward for a backward only branching, random for a random choice of forward or random branching every 1024 branches.

--gpu N
    start N worker that exercise the GPU. This specifies a 2-D texture image that allows the elements of an image array to be read by shaders, and render primitives using an opengl context.

--gpu-devnode DEVNAME
    specify the device node name of the GPU device, the default is /dev/dri/renderD128.

--gpu-frag N
    specify shader core usage per pixel, this sets N loops in the fragment shader.

--gpu-ops N
    stop gpu workers after N render loop operations.

--gpu-tex-size N
    specify upload texture N × N, by default this value is 4096 × 4096.

--gpu-xsize X
    use a framebuffer size of X pixels. The default is 256 pixels.

--gpu-ysize Y
    use a framebuffer size of Y pixels. The default is 256 pixels.

--gpu-upload N
    specify upload texture N times per frame, the default value is 1.

--handle N
    start N workers that exercise the name_to_handle_at(2) and open_by_handle_at(2) system calls. (Linux only).

--handle-ops N
    stop after N handle bogo operations.

--hash N
    start N workers that exercise various hashing functions. Random strings from 1 to 128 bytes are hashed and the hashing rate and chi squared is calculated from the number of hashes performed over a period of time. The chi squared value is the goodness-of-fit measure, it is the actual distribution of items in hash buckets versus the expected distribution of items. Typically a chi squared value of 0.95..1.05 indicates a good hash distribution.

--hash-method method
    specify the hashing method to use, by default all the hashing methods are cycled through. Methods available are:
    Method | Description
    all | cycle through all the hashing methods
    adler32 | Mark Adler checksum, a modification of the Fletcher checksum
    coffin | xor and 5 bit rotate left hash
    coffin32 | xor and 5 bit rotate left hash with 32 bit fetch optimization
    crc32c | compute CRC32C (Castagnoli CRC32) integer hash
    djb2a | Dan Bernstein hash using the xor variant
    fnv1a | FNV-1a Fowler-Noll-Vo hash using the xor then multiply variant
    jenkin | Jenkin's integer hash
    kandr | Kernighan and Richie's multiply by 31 and add hash from "The C Programming Language", 2nd Edition
    knuth | Donald E. Knuth's hash from "The Art Of Computer Programming", Volume 3, chapter 6.4
    loselose | Kernighan and Richie's simple hash from "The C Programming Language", 1st Edition
    mid5 | xor shift hash of the middle 5 characters of the string. Designed by Colin Ian King
    muladd32 | simple multiply and add hash using 32 bit math and xor folding of overflow
    muladd64 | simple multiply and add hash using 64 bit math and xor folding of overflow
    mulxror32 | 32 bit multiply, xor and rotate right. Mangles 32 bits where possible. Designed by Colin Ian King
    mulxror64 | 64 bit multiply, xor and rotate right. 64 Bit version of mulxror32
    murmur3_32 | murmur3_32 hash, Austin Appleby's Murmur3 hash, 32 bit variant
    nhash | exim's nhash.
    pjw | a non-cryptographic hash function created by Peter J. Weinberger of AT&T Bell Labs, used in UNIX ELF object files
    sdbm | sdbm hash as used in the SDBM database and GNU awk
    sedgwick | simple hash from Robert Sedgwick's C programming book
    sobel | Justin Sobel's bitwise shift hash
    x17 | multiply by 17 and add. The multiplication can be optimized down to a fast right shift by 4 and add on some architectures
    xor | simple rotate shift and xor of values
    xorror32 | 32 bit exclusive-or with right rotate hash, a fast string hash, designed by Colin Ian King
    xorror64 | 64 bit version of xorror32
    xxhash | the "Extremely fast" hash in non-streaming mode

--hash-ops N
    stop after N hashing rounds

-d N, --hdd N
    start N workers continually writing, reading and removing temporary files. The default mode is to stress test sequential writes and reads. With the --aggressive option enabled without any --hdd-opts options the hdd stressor will work through all the --hdd-opt options one by one to cover a range of I/O options.

--hdd-bytes N
    write N bytes for each hdd process, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--hdd-opts list
    specify various stress test options as a comma separated list. Options are as follows:
    Option | Description
    direct | try to minimize cache effects of the I/O. File I/O writes are performed directly from user space buffers and synchronous transfer is also attempted. To guarantee synchronous I/O, also use the sync option.
    dsync | ensure output has been transferred to underlying hardware and file metadata has been updated (using the O_DSYNC open flag). This is equivalent to each write(2) being followed by a call to fdatasync(2). See also the fdatasync option.
    fadv-dontneed | advise kernel to expect the data will not be accessed in the near future.
    fadv-noreuse | advise kernel to expect the data to be accessed only once.
    fadv-normal | advise kernel there are no explicit access pattern for the data. This is the default advice assumption.
    fadv-rnd | advise kernel to expect random access patterns for the data.
    fadv-seq | advise kernel to expect sequential access patterns for the data.
    fadv-willneed | advise kernel to expect the data to be accessed in the near future.
    fsync | flush all modified in-core data after each write to the output device using an explicit fsync(2) call.
    fdatasync | similar to fsync, but do not flush the modified metadata unless metadata is required for later data reads to be handled correctly. This uses an explicit fdatasync(2) call.
    iovec | use readv/writev multiple buffer I/Os rather than read/write. Instead of 1 read/write operation, the buffer is broken into an iovec of 16 buffers.
    noatime | do not update the file last access timestamp, this can reduce metadata writes.
    sync | ensure output has been transferred to underlying hardware (using the O_SYNC open flag). This is equivalent to a each write(2) being followed by a call to fsync(2). See also the fsync option.
    rd-rnd | read data randomly. By default, written data is not read back, however, this option will force it to be read back randomly.
    rd-seq | read data sequentially. By default, written data is not read back, however, this option will force it to be read back sequentially.
    syncfs | write all buffered modifications of file metadata and data on the filesystem that contains the hdd worker files.
    utimes | force update of file timestamp which may increase metadata writes.
    wr-rnd | write data randomly. The wr-seq option cannot be used at the same time.
    wr-seq | write data sequentially. This is the default if no write modes are specified.

Note that some of these options are mutually exclusive, for example, there can be only one method of writing or reading. Also, fadvise flags may be mutually exclusive, for example fadv-willneed cannot be used with fadv-dontneed.

--hdd-ops N
    stop hdd stress workers after N bogo operations.

--hdd-write-size N
    specify size of each write in bytes. Size can be from 1 byte to 4MB.

--heapsort N
    start N workers that sort 32 bit integers using the BSD heapsort.

--heapsort-ops N
    stop heapsort stress workers after N bogo heapsorts.

--heapsort-size N
    specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--hrtimers N
    start N workers that exercise high resolution times at a high frequency. Each stressor starts 32 processes that run with random timer intervals of 0..499999 nanoseconds. Running this stressor with appropriate privilege will run these with the SCHED_RR policy.

--hrtimers-adjust
    enable automatic timer rate adjustment to try to maximize the hrtimer frequency. The signal rate is measured every 0.1 seconds and the hrtimer delay is adjusted to try and set the optimal hrtimer delay to generate the highest hrtimer rates.

--hrtimers-ops N
    stop hrtimers stressors after N timer event bogo operations

--hsearch N
    start N workers that search a 80% full hash table using hsearch(3). By default, there are 8192 elements inserted into the hash table. This is a useful method to exercise access of memory and processor cache.

--hsearch-ops N
    stop the hsearch workers after N bogo hsearch operations are completed.

--hsearch-size N
    specify the number of hash entries to be inserted into the hash table. Size can be from 1K to 4M.

--icache N
    start N workers that stress the instruction cache by forcing instruction cache reloads.

--icache-ops N
    stop the icache workers after N bogo icache operations are completed.

--icmp-flood N
    start N workers that flood localhost with randonly sized ICMP ping packets. This stressor requires the CAP_NET_RAW capbility.

--icmp-flood-ops N
    stop icmp flood workers after N ICMP ping packets have been sent.

--idle-scan N
    start N workers that scan the idle page bitmap across a range of physical pages. This sets and checks for idle pages via the idle page tracking interface /sys/kernel/mm/page_idle/bitmap. This is for Linux only.

--idle-scan-ops N
    stop after N bogo page scan operations. Currently one bogo page scan operation is equivalent to setting and checking 64 physical pages.

--idle-page N
    start N workers that walks through every page exercising the Linux /sys/kernel/mm/page_idle/bitmap interface. Requires CAP_SYS_RESOURCE capability.

--idle-page-ops N
    stop after N bogo idle page operations.

--inode-flags N
    start N workers that exercise inode flags using the FS_IOC_GETFLAGS and FS_IOC_SETFLAGS ioctl(2). This attempts to apply all the available inode flags onto a directory and file even if the underlying file system may not support these flags (errors are just ignored). Each worker runs 4 threads that exercise the flags on the same directory and file to try to force races. This is a Linux only stressor, see ioctl_iflags(2) for more details.

--inode-flags-ops N
    stop the inode-flags workers after N ioctl flag setting attempts.

--inotify N
    start N workers performing file system activities such as making/deleting files/directories, moving files, etc. to stress exercise the various inotify events (Linux only).

--inotify-ops N
    stop inotify stress workers after N inotify bogo operations.

-i N, --io N
    start N workers continuously calling sync(2) to commit buffer cache to disk. This can be used in conjunction with the --hdd stressor. This is a legacy stressor that is compatible with the orignal stress tool.

--io-ops N
    stop io stress workers after N bogo operations.

--iomix N
    start N workers that perform a mix of sequential, random and memory mapped read/write operations as well as random copy file read/writes, forced sync'ing and (if run as root) cache dropping. Multiple child processes are spawned to all share a single file and perform different I/O operations on the same file.

--iomix-bytes N
    write N bytes for each iomix worker process, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--iomix-ops N
    stop iomix stress workers after N bogo iomix I/O operations.

--ioport N
    start N workers than perform bursts of 16 reads and 16 writes of ioport 0x80 (x86 Linux systems only). I/O performed on x86 platforms on port 0x80 will cause delays on the CPU performing the I/O.

--ioport-ops N
    stop the ioport stressors after N bogo I/O operations

--ioport-opts [ in | out | inout ]
    specify if port reads in, port read writes out or reads and writes are to be performed. The default is both in and out.

--ioprio N
    start N workers that exercise the ioprio_get(2) and ioprio_set(2) system calls (Linux only).

--ioprio-ops N
    stop after N io priority bogo operations.

--io-uring N
    start N workers that perform iovec write and read I/O operations using the Linux io-uring interface. On each bogo-loop 1024 × 512 byte writes and 1024 × reads are performed on a temporary file.

--io-uring-ops
    stop after N rounds of write and reads.

--ipsec-mb N
    start N workers that perform cryptographic processing using the highly optimized Intel Multi-Buffer Crypto for IPsec library. Depending on the features available, SSE, AVX, AVX and AVX512 CPU features will be used on data encrypted by SHA, DES, CMAC, CTR, HMAC MD5, HMAC SHA1 and HMAC SHA512 cryptographic routines. This is only available for x86-64 modern Intel CPUs.

--ipsec-mb-feature [ sse | avx | avx2 | avx512 ]
    Just use the specified processor CPU feature. By default, all the available features for the CPU are exercised.

--ipsec-mb-jobs N
    Process N multi-block rounds of cryptographic processing per iteration. The default is 256.

--ipsec-mb-method [ all | cmac | ctr | des | hmac-md5 | hmac-sha1 | hmac-sha512 | sha ]
    Select the ipsec-mb crypto/integrity method.

--ipsec-mb-ops N
    stop after N rounds of processing of data using the cryptographic routines.

--itimer N
    start N workers that exercise the system interval timers. This sets up an ITIMER_PROF itimer that generates a SIGPROF signal. The default frequency for the itimer is 1 MHz, however, the Linux kernel will set this to be no more that the jiffy setting, hence high frequency SIGPROF signals are not normally possible. A busy loop spins on getitimer(2) calls to consume CPU and hence decrement the itimer based on amount of time spent in CPU and system time.

--itimer-freq F
    run itimer at F Hz; range from 1 to 1000000 Hz. Normally the highest frequency is limited by the number of jiffy ticks per second, so running above 1000 Hz is difficult to attain in practice.

--itimer-ops N
    stop itimer stress workers after N bogo itimer SIGPROF signals.

--itimer-rand
    select an interval timer frequency based around the interval timer frequency +/- 12.5% random jitter. This tries to force more variability in the timer interval to make the scheduling less predictable.

--jpeg N
    start N workers that use jpeg compression on a machine generated plasma field image. The default image is a plasma field, however different image types may be selected. The starting raster line is changed on each compression iteration to cycle around the data.

--jpeg-height H
    use a RGB sample image height of H pixels. The default is 512 pixels.

--jpeg-image [ brown | flat | gradient | noise | plasma | xstripes ]
    select the source image type to be compressed. Available image types are:
    Type | Description
    brown | brown noise, red and green values vary by a 3 bit value, blue values vary by a 2 bit value.
    flat | a single random colour for the entire image.
    gradient | linear gradient of the red, green and blue components across the width and height of the image.
    noise | random white noise for red, green, blue values.
    plasma | plasma field with smooth colour transitions and hard boundary edges.
    xstripes | a random colour for each horizontal line.

--jpeg-ops N
    stop after N jpeg compression operations.

--jpeg-width H
    use a RGB sample image width of H pixels. The default is 512 pixels.

--jpeg-quality Q
    use the compression quality Q. The range is 1..100 (1 lowest, 100 highest), with a default of 95

--judy N
    start N workers that insert, search and delete 32 bit integers in a Judy array using a predictable yet sparse array index. By default, there are 131072 integers used in the Judy array. This is a useful method to exercise random access of memory and processor cache.

--judy-ops N
    stop the judy workers after N bogo judy operations are completed.

--judy-size N
    specify the size (number of 32 bit integers) in the Judy array to exercise. Size can be from 1K to 4M 32 bit integers.

--kcmp N
    start N workers that use kcmp(2) to compare parent and child processes to determine if they share kernel resources. Supported only for Linux and requires CAP_SYS_PTRACE capability.

--kcmp-ops N
    stop kcmp workers after N bogo kcmp operations.

--key N
    start N workers that create and manipulate keys using add_key(2) and ketctl(2). As many keys are created as the per user limit allows and then the following keyctl commands are exercised on each key: KEYCTL_SET_TIMEOUT, KEYCTL_DESCRIBE, KEYCTL_UPDATE, KEYCTL_READ, KEYCTL_CLEAR and KEYCTL_INVALIDATE.

--key-ops N
    stop key workers after N bogo key operations.

--kill N
    start N workers sending SIGUSR1 kill signals to a SIG_IGN signal handler in the stressor and SIGUSR1 kill signal to a child stressor with a SIGUSR1 handler. Most of the process time will end up in kernel space.

--kill-ops N
    stop kill workers after N bogo kill operations.

--klog N
    start N workers exercising the kernel syslog(2) system call. This will attempt to read the kernel log with various sized read buffers. Linux only.

--klog-ops N
    stop klog workers after N syslog operations.

--kvm N
    start N workers that create, run and destroy a minimal virtual machine. The virtual machine reads, increments and writes to port 0x80 in a spin loop and the stressor handles the I/O transactions. Currently for x86 and Linux only.

--kvm-ops N
    stop kvm stressors after N virtual machines have been created, run and destroyed.

--l1cache N
    start N workers that exercise the CPU level 1 cache with reads and writes. A cache aligned buffer that is twice the level 1 cache size is read and then written in level 1 cache set sized steps over each level 1 cache set. This is designed to exercise cache block evictions. The bogo-op count measures the number of million cache lines touched. Where possible, the level 1 cache geometry is determined from the kernel, however, this is not possible on some architectures or kernels, so one may need to specify these manually. One can specify 3 out of the 4 cache geometric parameters, these are as follows:

--l1cache-line-size N
    specify the level 1 cache line size (in bytes)

--l1cache-method [ forward | random | reverse ]
    select the method of exercising a l1cache sized buffer. The default is a forward scan, random picks random bytes to exercise, reverse scans in reverse.

--l1cache-mlock
    attempt to mlock the l1cache size buffer into memory to prevent it from being swapped out.

--l1cache-ops N
    specify the number of cache read/write bogo-op loops to run

--l1cache-sets N
    specify the number of level 1 cache sets

--l1cache-size N
    specify the level 1 cache size (in bytes)

--l1cache-ways N
    specify the number of level 1 cache ways

--landlock N
    start N workers that exercise Linux 5.13 landlocking. A range of landlock_create_ruleset flags are exercised with a read only file rule to see if a directory can be accessed and a read-write file create can be blocked. Each ruleset attempt is exercised in a new child context and this is the limiting factor on the speed of the stressor.

--landlock-ops N
    stop the landlock stressors after N landlock ruleset bogo operations.

--lease N
    start N workers locking, unlocking and breaking leases via the fcntl(2) F_SETLEASE operation. The parent processes continually lock and unlock a lease on a file while a user selectable number of child processes open the file with a non-blocking open to generate SIGIO lease breaking notifications to the parent. This stressor is only available if F_SETLEASE, F_WRLCK and F_UNLCK support is provided by fcntl(2).

--lease-breakers N
    start N lease breaker child processes per lease worker. Normally one child is plenty to force many SIGIO lease breaking notification signals to the parent, however, this option allows one to specify more child processes if required.

--lease-ops N
    stop lease workers after N bogo operations.

--link N
    start N workers creating and removing hardlinks.

--link-ops N
    stop link stress workers after N bogo operations.

--link-sync
    sync dirty data and metadata to disk.

--list N
    start N workers that exercise list data structures. The default is to add, find and remove 5,000 64 bit integers into circleq (doubly linked circle queue), list (doubly linked list), slist (singly linked list), slistt (singly linked list using tail), stailq (singly linked tail queue) and tailq (doubly linked tail queue) lists. The intention of this stressor is to exercise memory and cache with the various list operations.

--list-method [ all | circleq | list | slist | stailq | tailq ]
    specify the list to be used. By default, all the list methods are used (the 'all' option).

--list-ops N
    stop list stressors after N bogo ops. A bogo op covers the addition, finding and removing all the items into the list(s).

--list-size N
    specify the size of the list, where N is the number of 64 bit integers to be added into the list.

--llc-affinity N
    start N workers that exercise the lower-level cache (LLC) by read/write activity across a LLC sized buffer and then changing CPU affinity after each round of read/writes. This can cause non-local memory stalls and LLC read/write misses.

--llc-affinity-mlock
    attempt to mlock the LLC sized buffer into memory to prevent it from being swapped out.

--llc-affinity-ops N
    stop after N rounds of LLC read/writes.

--loadavg N
    start N workers that attempt to create thousands of pthreads that run at the lowest nice priority to force very high load averages. Linux systems will also perform some I/O writes as pending I/O is also factored into system load accounting.

--loadavg-max N
    set the maximum number of pthreads to create to N. N may be reduced if there is as system limit on the number of pthreads that can be created.

--loadavg-ops N
    stop loadavg workers after N bogo scheduling yields by the pthreads have been reached.

--lockbus N
    start N workers that rapidly lock and increment 64 bytes of randomly chosen memory from a 16MB mmap'd region (Intel x86 and ARM CPUs only). This will cause cacheline misses and stalling of CPUs.

--lockbus-nosplit
    disable split locks that lock across cache line boundaries.

--lockbus-ops N
    stop lockbus workers after N bogo operations.

--locka N
    start N workers that randomly lock and unlock regions of a file using the POSIX advisory locking mechanism (see fcntl(2), F_SETLK, F_GETLK). Each worker creates a 1024 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--locka-ops N
    stop locka workers after N bogo locka operations.

--lockf N
    start N workers that randomly lock and unlock regions of a file using the POSIX lockf(3) locking mechanism. Each worker creates a 64 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--lockf-ops N
    stop lockf workers after N bogo lockf operations.

--lockf-nonblock
    instead of using blocking F_LOCK lockf(3) commands, use non-blocking F_TLOCK commands and re-try if the lock failed. This creates extra system call overhead and CPU utilisation as the number of lockf workers increases and should increase locking contention.

--lockofd N
    start N workers that randomly lock and unlock regions of a file using the Linux open file description locks (see fcntl(2), F_OFD_SETLK, F_OFD_GETLK). Each worker creates a 1024 KB file and attempts to hold a maximum of 1024 concurrent locks with a child process that also tries to hold 1024 concurrent locks. Old locks are unlocked in a first-in, first-out basis.

--lockofd-ops N
    stop lockofd workers after N bogo lockofd operations.

--longjmp N
    start N workers that exercise setjmp(3)/longjmp(3) by rapid looping on longjmp calls.

--longjmp-ops N
    stop longjmp stress workers after N bogo longjmp operations (1 bogo op is 1000 longjmp calls).

--loop N
    start N workers that exercise the loopback control device. This creates 2MB loopback devices, expands them to 4MB, performs some loopback status information get and set operations and then destoys them. Linux only and requires CAP_SYS_ADMIN capability.

--loop-ops N
    stop after N bogo loopback creation/deletion operations.

--lsearch N
    start N workers that linear search a unsorted array of 32 bit integers using lsearch(3). By default, there are 8192 elements in the array. This is a useful method to exercise sequential access of memory and processor cache.

--lsearch-ops N
    stop the lsearch workers after N bogo lsearch operations are completed.

--lsearch-size N
    specify the size (number of 32 bit integers) in the array to lsearch. Size can be from 1K to 4M.

--madvise N
    start N workers that apply random madvise(2) advise settings on pages of a 4MB file backed shared memory mapping.

--madvise-hwpoison
    enable MADV_HWPOISON page poisoning (if available, only when run as root). This will page poison a few pages and will cause kernel error messages to be reported.

--madvise-ops N
    stop madvise stressors after N bogo madvise operations.

--malloc N
    start N workers continuously calling malloc(3), calloc(3), realloc(3), posix_memalign(3), aligned_alloc(3), memalign(3) and free(3). By default, up to 65536 allocations can be active at any point, but this can be altered with the --malloc-max option. Allocation, reallocation and freeing are chosen at random; 50% of the time memory is allocation (via one of malloc, calloc or realloc, posix_memalign, aligned_alloc, memalign) and 50% of the time allocations are free'd. Allocation sizes are also random, with the maximum allocation size controlled by the --malloc-bytes option, the default size being 64K. The worker is re-started if it is killed by the out of memory (OOM) killer.

--malloc-bytes N
    maximum per allocation/reallocation size. Allocations are randomly selected from 1 to N bytes. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Large allocation sizes cause the memory allocator to use mmap(2) rather than expanding the heap using brk(2).

--malloc-max N
    maximum number of active allocations allowed. Allocations are chosen at random and placed in an allocation slot. Because about 50%/50% split between allocation and freeing, typically half of the allocation slots are in use at any one time.

--malloc-mlock
    attempt to mlock the allocations into memory to prevent them from being swapped out.

--malloc-ops N
    stop after N malloc bogo operations. One bogo operations relates to a successful malloc(3), calloc(3) or realloc(3).

--malloc-pthreads N
    specify number of malloc stressing concurrent pthreads to run. The default is 0 (just one main process, no pthreads). This option will do nothing if pthreads are not supported.

--malloc-thresh N
    specify the threshold where malloc uses mmap(2) instead of sbrk(2) to allocate more memory. This is only available on systems that provide the GNU C mallopt(3) tuning function.

--malloc-touch
    touch every allocated page to force pages to be populated in memory. This will increase the memory pressure and exercise the virtual memory harder. By default the malloc stressor will madvise pages into memory or use mincore to check for non-resident memory pages and try to force them into memory; this option aggressively forces pages to be memory resident.

--malloc-zerofree
    zero allocated memory before free'ing. This can be useful in touching broken allocations and triggering failures. Also useful for forcing extra cache/memory writes.

--matrix N
    start N workers that perform various matrix operations on floating point values. Testing on 64 bit x86 hardware shows that this provides a good mix of memory, cache and floating point operations and is an excellent way to make a CPU run hot. By default, this will exercise all the matrix stress methods one by one. One can specify a specific matrix stress method with the --matrix-method option.

--matrix-method method
    specify a matrix stress method. Available matrix stress methods are described as follows:
    Method | Description
    all | iterate over all the below matrix stress methods
    add | add two N × N matrices
    copy | copy one N × N matrix to another
    div | divide an N × N matrix by a scalar
    frobenius | Frobenius product of two N × N matrices
    hadamard | Hadamard product of two N × N matrices
    identity | create an N × N identity matrix
    mean | arithmetic mean of two N × N matrices
    mult | multiply an N × N matrix by a scalar
    negate | negate an N × N matrix
    prod | product of two N × N matrices
    sub | subtract one N × N matrix from another N × N matrix
    square | multiply an N × N matrix by itself
    trans | transpose an N × N matrix
    zero | zero an N × N matrix

--matrix-ops N
    stop matrix stress workers after N bogo operations.

--matrix-size N
    specify the N × N size of the matrices. Smaller values result in a floating point compute throughput bound stressor, where as large values result in a cache and/or memory bandwidth bound stressor.

--matrix-yx
    perform matrix operations in order y by x rather than the default x by y. This is suboptimal ordering compared to the default and will perform more data cache stalls.

--matrix-3d N
    start N workers that perform various 3D matrix operations on floating point values. Testing on 64 bit x86 hardware shows that this provides a good mix of memory, cache and floating point operations and is an excellent way to make a CPU run hot. By default, this will exercise all the 3D matrix stress methods one by one. One can specify a specific 3D matrix stress method with the --matrix-3d-method option.

--matrix-3d-method method
    specify a 3D matrix stress method. Available 3D matrix stress methods are described as follows:
    Method | Description
    all | iterate over all the below matrix stress methods
    add | add two N × N × N matrices
    copy | copy one N × N × N matrix to another
    div | divide an N × N × N matrix by a scalar
    frobenius | Frobenius product of two N × N × N matrices
    hadamard | Hadamard product of two N × N × N matrices
    identity | create an N × N × N identity matrix
    mean | arithmetic mean of two N × N × N matrices
    mult | multiply an N × N × N matrix by a scalar
    negate | negate an N × N × N matrix
    sub | subtract one N × N × N matrix from another N × N × N matrix
    trans | transpose an N × N × N matrix
    zero | zero an N × N × N matrix

--matrix-3d-ops N
    stop the 3D matrix stress workers after N bogo operations.

--matrix-3d-size N
    specify the N × N × N size of the matrices. Smaller values result in a floating point compute throughput bound stressor, where as large values result in a cache and/or memory bandwidth bound stressor.

--matrix-3d-zyx
    perform matrix operations in order z by y by x rather than the default x by y by z. This is suboptimal ordering compared to the default and will perform more data cache stalls.

--mcontend N
    start N workers that produce memory contention read/write patterns. Each stressor runs with 5 threads that read and write to two different mappings of the same underlying physical page. Various caching operations are also exercised to cause sub-optimal memory access patterns. The threads also randomly change CPU affinity to exercise CPU and memory migration stress.

--mcontend-ops N
    stop mcontend stressors after N bogo read/write operations.

--membarrier N
    start N workers that exercise the membarrier system call (Linux only).

--membarrier-ops N
    stop membarrier stress workers after N bogo membarrier operations.

--memcpy N
    start N workers that copies data to and from a buffer using memcpy(3) and then move the data in the buffer with memmove(3) with 3 different alignments. This will exercise the data cache and memory copying.

--memcpy-method [ all | libc | builtin | naive | naive_o0 .. naive_o3 ]
    specify a memcpy copying method. Available memcpy methods are described as follows:
    Method | Description
    all | use libc, builtin and naïve methods
    libc | use libc memcpy and memmove functions, this is the default
    builtin | use the compiler built in optimized memcpy and memmove functions
    naive | use naïve byte by byte copying and memory moving build with default compiler optimization flags
    naive_o0 | use unoptimized naïve byte by byte copying and memory moving
    naive_o1 | use unoptimized naïve byte by byte copying and memory moving with -O1 optimization
    naive_o2 | use optimized naïve byte by byte copying and memory moving build with -O2 optimization and where possible use CPU specific optimizations
    naive_o3 | use optimized naïve byte by byte copying and memory moving build with -O3 optimization and where possible use CPU specific optimizations

--memcpy-ops N
    stop memcpy stress workers after N bogo memcpy operations.

--memfd N
    start N workers that create allocations of 1024 pages using memfd_create(2) and ftruncate(2) for allocation and mmap(2) to map the allocation into the process address space. (Linux only).

--memfd-bytes N
    allocate N bytes per memfd stress worker, the default is 256MB. One can specify the size in as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--memfd-fds N
    create N memfd file descriptors, the default is 256. One can select 8 to 4096 memfd file descriptions with this option.

--memfd-mlock
    attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--memfd-ops N
    stop after N memfd-create(2) bogo operations.

--memhotplug N
    start N workers that offline and online memory hotplug regions. Linux only and requires CAP_SYS_ADMIN capabilities.

--memhotplug-ops N
    stop memhotplug stressors after N memory offline and online bogo operations.

--memrate N
    start N workers that exercise a buffer with 1024, 512, 256, 128, 64, 32, 16 and 8 bit reads and writes. 1024, 512 and 256 reads and writes are available with compilers that support integer vectors. x86-64 cpus that support uncached (non-temporal "nt") writes also exercise 128, 64 and 32 writes providing higher write rates than the normal cached writes. x86-64 also exercises repeated string stores using 64, 32, 16 and 8 bit writes. CPUs that support prefetching reads also exercise 64 prefetched "pf" reads. This memory stressor allows one to also specify the maximum read and write rates. The stressors will run at maximum speed if no read or write rates are specified.

--memrate-bytes N
    specify the size of the memory buffer being exercised. The default size is 256MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g, or cache sizes with L1, L2, L3 or LLC (lower level cache size).

--memrate-flush
    flush cache between each memory exercising test to remove caching benefits in memory rate metrics.

--memrate-ops N
    stop after N bogo memrate operations.

--memrate-rd-mbs N
    specify the maximum allowed read rate in MB/sec. The actual read rate is dependent on scheduling jitter and memory accesses from other running processes.

--memrate-wr-mbs N
    specify the maximum allowed read rate in MB/sec. The actual write rate is dependent on scheduling jitter and memory accesses from other running processes.

--memthrash N
    start N workers that thrash and exercise a 16MB buffer in various ways to try and trip thermal overrun. Each stressor will start 1 or more threads. The number of threads is chosen so that there will be at least 1 thread per CPU. Note that the optimal choice for N is a value that divides into the number of CPUs.

--memthrash-method method
    specify a memthrash stress method. Available memthrash stress methods are described as follows:
    Method | Description
    all | iterate over all the below memthrash methods
    chunk1 | memset 1 byte chunks of random data into random locations
    chunk8 | memset 8 byte chunks of random data into random locations
    chunk64 | memset 64 byte chunks of random data into random locations
    chunk256 | memset 256 byte chunks of random data into random locations
    chunkpage | memset page size chunks of random data into random locations
    copy128 | copy 128 byte chunks from chunk N + 1 to chunk N with streaming reads and writes with 128 bit memory accesses where possible.
    flip | flip (invert) all bits in random locations
    flush | flush cache line in random locations
    lock | lock randomly choosing locations (Intel x86 and ARM CPUs only)
    matrix | treat memory as a 2 × 2 matrix and swap random elements
    memmove | copy all the data in buffer to the next memory location
    memset | memset the memory with random data
    memset64 | memset the memory with a random 64 bit value in 64 byte chunks using non-temporal stores if possible or normal stores as a fallback
    memsetstosd | memset the memory using x86 32 bit rep stosd instruction (x86 only)
    mfence | stores with write serialization
    numa | memory bind pages across numa nodes
    prefetch | prefetch data at random memory locations
    random | randomly run any of the memthrash methods except for 'random' and 'all'
    spinread | spin loop read the same random location 2↑19 times
    spinwrite | spin loop write the same random location 2↑19 times
    swap | step through memory swapping bytes in steps of 65 and 129 byte strides
    swap64 | work through memory swapping adjacent 64 byte chunks
    swapfwdrev | swap 64 bit values from start to end and work towards the middle and then from end to start and work towards the middle.
    tlb | work through memory in sub-optimial strides of prime multiples of the cache line size with reads and then writes to cause Translation Lookaside Buffer (TLB) misses.

--memthrash-ops N
    stop after N memthrash bogo operations.

--mergesort N
    start N workers that sort 32 bit integers using the BSD mergesort.

--mergesort-ops N
    stop mergesort stress workers after N bogo mergesorts.

--mergesort-size N
    specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--mincore N
    start N workers that walk through all of memory 1 page at a time checking if the page mapped and also is resident in memory using mincore(2). It also maps and unmaps a page to check if the page is mapped or not using mincore(2).

--mincore-ops N
    stop after N mincore bogo operations. One mincore bogo op is equivalent to a 300 mincore(2) calls. --mincore-random instead of walking through pages sequentially, select pages at random. The chosen address is iterated over by shifting it right one place and checked by mincore until the address is less or equal to the page size.

--misaligned N
    start N workers that perform misaligned read and writes. By default, this will exercise 128 bit misaligned read and writes in 8 × 16 bits, 4 × 32 bits, 2 × 64 bits and 1 × 128 bits at the start of a page boundary, at the end of a page boundary and over a cache boundary. Misaligned read and writes operate at 1 byte offset from the natural alignment of the data type. On some architectures this can cause SIGBUS, SIGILL or SIGSEGV, these are handled and the misaligned stressor method causing the error is disabled.

--misaligned-method method
    Available misaligned stress methods are described as follows:
    Method | Description
    all | iterate over all the following misaligned methods
    int16rd | 8 × 16 bit integer reads
    int16wr | 8 × 16 bit integer writes
    int16inc | 8 × 16 bit integer increments
    int16atomic | 8 × 16 bit atomic integer increments
    int32rd | 4 × 32 bit integer reads
    int32wr | 4 × 32 bit integer writes
    int32wtnt | 4 × 32 bit non-temporal stores (x86 only)
    int32inc | 4 × 32 bit integer increments
    int32atomic | 4 × 32 bit atomic integer increments
    int64rd | 2 × 64 bit integer reads
    int64wr | 2 × 64 bit integer writes
    int64wtnt | 4 × 64 bit non-temporal stores (x86 only)
    int64inc | 2 × 64 bit integer increments
    int64atomic | 2 × 64 bit atomic integer increments
    int128rd | 1 × 128 bit integer reads
    int128wr | 1 × 128 bit integer writes
    int128inc | 1 × 128 bit integer increments
    int128atomic | 1 × 128 bit atomic integer increments

Note that some of these options (128 bit integer and/or atomic operations) may not be available on some systems.

--misaligned-ops N
    stop after N misaligned bogo operation. A misaligned bogo op is equivalent to 65536 × 128 bit reads or writes.

--mknod N
    start N workers that create and remove fifos, empty files and named sockets using mknod and unlink.

--mknod-ops N
    stop directory thrash workers after N bogo mknod operations.

--mlock N
    start N workers that lock and unlock memory mapped pages using mlock(2), munlock(2), mlockall(2) and munlockall(2). This is achieved by the mapping of three contiguous pages and then locking the second page, hence ensuring non-contiguous pages are locked . This is then repeated until the maximum allowed mlocks or a maximum of 262144 mappings are made. Next, all future mappings are mlocked and the worker attempts to map 262144 pages, then all pages are munlocked and the pages are unmapped.

--mlock-ops N
    stop after N mlock bogo operations.

--mlockmany N
    start N workers that fork off a default of 1024 child processes in total; each child will attempt to anonymously mmap and mlock the maximum allowed mlockable memory size. The stress test attempts to avoid swapping by tracking low memory and swap allocations (but some swapping may occur). Once either the maximum number of child process is reached or all mlockable in-core memory is locked then child processes are killed and the stress test is repeated.

--mlockmany-ops N
    stop after N mlockmany (mmap and mlock) operations.

--mlockmany-procs N
    set the number of child processes to create per stressor. The default is to start a maximum of 1024 child processes in total across all the stressors. This option allows the setting of N child processes per stressor.

--mmap N
    start N workers continuously calling mmap(2)/munmap(2). The initial mapping is a large chunk (size specified by --mmap-bytes) followed by pseudo-random 4K unmappings, then pseudo-random 4K mappings, and then linear 4K unmappings. Note that this can cause systems to trip the kernel OOM killer on Linux systems if not enough physical memory and swap is not available. The MAP_POPULATE option is used to populate pages into memory on systems that support this. By default, anonymous mappings are used, however, the --mmap-file and --mmap-async options allow one to perform file based mappings if desired.

--mmap-async
    enable file based memory mapping and use asynchronous msync'ing on each page, see --mmap-file.

--mmap-bytes N
    allocate N bytes per mmap stress worker, the default is 256MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--mmap-file
    enable file based memory mapping and by default use synchronous msync'ing on each page.

--mmap-mlock
    attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mmap-mmap2
    use mmap2 for 4K page aligned offsets if mmap2 is available, otherwise fall back to mmap.

--mmap-mprotect
    change protection settings on each page of memory. Each time a page or a group of pages are mapped or remapped then this option will make the pages read-only, write-only, exec-only, and read-write.

--mmap-odirect
    enable file based memory mapping and use O_DIRECT direct I/O.

--mmap-ops N
    stop mmap stress workers after N bogo operations.

--mmap-osync
    enable file based memory mapping and used O_SYNC synchronous I/O integrity completion.

--mmapaddr N
    start N workers that memory map pages at a random memory location that is not already mapped. On 64 bit machines the random address is randomly chosen 32 bit or 64 bit address. If the mapping works a second page is memory mapped from the first mapped address. The stressor exercises mmap/munmap, mincore and segfault handling.

--mmapaddr-mlock
    attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mmapaddr-ops N
    stop after N random address mmap bogo operations.

--mmapfork N
    start N workers that each fork off 32 child processes, each of which tries to allocate some of the free memory left in the system (and trying to avoid any swapping). The child processes then hint that the allocation will be needed with madvise(2) and then memset it to zero and hint that it is no longer needed with madvise before exiting. This produces significant amounts of VM activity, a lot of cache misses and with minimal swapping.

--mmapfork-ops N
    stop after N mmapfork bogo operations.

--mmapfixed N
    start N workers that perform fixed address allocations from the top virtual address down to 128K. The allocated sizes are from 1 page to 8 pages and various random mmap flags are used MAP_SHARED/MAP_PRIVATE, MAP_LOCKED, MAP_NORESERVE, MAP_POPULATE. If successfully map'd then the allocation is remap'd first to a large range of addresses based on a random start and finally an address that is several pages higher in memory. Mappings and remappings are madvised with random madvise options to further exercise the mappings.

--mmapfixed-mlock
    attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mmapfixed-ops N
    stop after N mmapfixed memory mapping bogo operations.

--mmaphuge N
    start N workers that attempt to mmap a set of huge pages and large huge page sized mappings. Successful mappings are madvised with MADV_NOHUGEPAGE and MADV_HUGEPAGE settings and then 1/64th of the normal small page size pages are touched. Finally, an attempt to unmap a small page size page at the end of the mapping is made (these may fail on huge pages) before the set of pages are unmapped. By default 8192 mappings are attempted per round of mappings or until swapping is detected.

--mmaphuge-mlock
    attempt to mlock mmap'd huge pages into memory causing more memory pressure by preventing pages from swapped out.

--mmaphuge-mmaps N
    set the number of huge page mappings to attempt in each round of mappings. The default is 8192 mappings.

--mmaphuge-ops N
    stop after N mmaphuge bogo operations

--mmapmany N
    start N workers that attempt to create the maximum allowed per-process memory mappings. This is achieved by mapping 3 contiguous pages and then unmapping the middle page hence splitting the mapping into two. This is then repeated until the maximum allowed mappings or a maximum of 262144 mappings are made.

--mmapmany-mlock
    attempt to mlock mmap'd huge pages into memory causing more memory pressure by preventing pages from swapped out.

--mmapmany-ops N
    stop after N mmapmany bogo operations

--module N
    start N workers that use finit_module() to load the module specified or the hello test module, if is available. There are different ways to test loading modules. Using modprobe calls in a loop, using the kernel kernel module autoloader, and this stress-ng module stressor. To stress tests modprobe we can simply run the userspace modprobe program in a loop. To stress test the kernel module autoloader we can stress tests using the upstream kernel tools/testing/selftests/kmod/kmod.sh. This ends up calling modprobe in the end, and it has its own caps built-in to self protect the kernel from too many requests at the same time. The userspace modprobe call will also prevent calls if the same module exists already. The stress-ng modules stressor is designed to help stress test the finit_module() system call even if the module is already loaded, testing races that are otherwise hard to reproduce.

--module-name NAME
    NAME of the module to use, for example: test_module, xfs, ext4. By default test_module is used so CONFIG_TEST_LKM must be enabled in the kernel. The module dependencies must be loaded prior to running these stressor tests, as this stresses running finit_module() not using modprobe.

--module-no-modver
    ignore module modversions when using finit_module().

--module-no-vermag
    ignore module versions when using finit_module().

--module-no-unload
    do not unload the module right after loading it with finit_module().

--module-ops N
    stop after N module load/unload cycles

--mpfr N
    start N workers that exercise multi-precision floating point operations using the GNU Multi-Precision Floating Point Reliable library (mpfr). Operations computed are as follows:
    Method | Description
    apery | calculate Apery's constant ζ(3); the sum of 1/(n ↑ 3).
    cosine | compute cos(θ) for θ = 0 to 2π in 100 steps.
    euler | compute e using n (1 + (1 ÷ n)) ↑ n.
    exp | compute 1000 exponentials.
    log | computer 1000 natural logarithms.
    omega | compute the omega constant defined by Ωe↑Ω = 1 using efficient iteration of Ωn+1 = (1 + Ωn) / (1 + e↑Ωn).
    phi | compute the Golden Ratio φ using series.
    sine | compute sin(θ) for θ = 0 to 2π in 100 steps.
    nsqrt | compute square root using Newton-Raphson.

--mpfr-ops N
    stop workers after N iterations of various multi-precision floating point operations.

--mpfr-precision N
    specify the precision in binary digits of the floating point operations. The default is 1000 bits, the allowed range is 32 to 1000000 (very slow).

--mprotect N
    start N workers that exercise changing page protection settings and access memory after each change. 8 processes per worker contend with each other changing page proection settings on a shared memory region of just a few pages to cause TLB flushes. A read and write to the pages can cause segmentation faults and these are handled by the stressor. All combinations of page protection settings are exercised including invalid combinations.

--mprotect-ops N
    stop after N mprotect calls.

--mq N
    start N sender and receiver processes that continually send and receive messages using POSIX message queues. (Linux only).

--mq-ops N
    stop after N bogo POSIX message send operations completed.

--mq-size N
    specify size of POSIX message queue. The default size is 10 messages and most Linux systems this is the maximum allowed size for normal users. If the given size is greater than the allowed message queue size then a warning is issued and the maximum allowed size is used instead.

--mremap N
    start N workers continuously calling mmap(2), mremap(2) and munmap(2). The initial anonymous mapping is a large chunk (size specified by --mremap-bytes) and then iteratively halved in size by remapping all the way down to a page size and then back up to the original size. This worker is only available for Linux.

--mremap-bytes N
    initially allocate N bytes per remap stress worker, the default is 256MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--mremap-mlock
    attempt to mlock remap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--mremap-ops N
    stop mremap stress workers after N bogo operations.

--msg N
    start N sender and receiver processes that continually send and receive messages using System V message IPC.

--msg-bytes N
    specify the size of the message being sent and received. Range 4 to 8192 bytes, default is 4 bytes.

--msg-ops N
    stop after N bogo message send operations completed.

--msg-types N
    select the quality of message types (mtype) to use. By default, msgsnd sends messages with a mtype of 1, this option allows one to send messages types in the range 1..N to exercise the message queue receive ordering. This will also impact throughput performance.

--msync N
    start N stressors that msync data from a file backed memory mapping from memory back to the file and msync modified data from the file back to the mapped memory. This exercises the msync(2) MS_SYNC and MS_INVALIDATE sync operations.

--msync-bytes N
    allocate N bytes for the memory mapped file, the default is 256MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--msync-ops N
    stop after N msync bogo operations completed.

--msyncmany N
    start N stressors that memory map up to 32768 pages on the same page of a temporary file, change the first 32 bits in a page and msync the data back to the file. The other 32767 pages are examined to see if the 32 bit check value is msync'd back to these pages.

--msyncmany-ops N
    stop after N msync calls in the msyncmany stressors are completed.

--munmap N
    start N stressors that exercise unmapping of shared non-executable mapped regions of child processes (Linux only). The unmappings map shared memory regions page by page with a prime sized stride that creates many temporary mapping holes. One the unmappings are complete the child will exit and a new one is started. Note that this may trigger segmentation faults in the child process, these are handled where possible by forcing the child process to call _exit(2).

--munmap-ops N
    stop after N page unmappings.

--mutex N
    start N stressors that exercise pthread mutex locking and unlocking. If run with enough privilege then the FIFO scheduler is used and a random priority between 0 and 80% of the maximum FIFO priority level is selected for the locking operation. The minimum FIFO priority level is selected for the critical mutex section and unlocking operation to exercise random inverted priority scheduling.

--mutex-affinity
    enable random CPU affinity changing between mutex lock and unlock.

--mutex-ops N
    stop after N bogo mutex lock/unlock operations.

--mutex-procs N
    By default 2 threads are used for locking/unlocking on a single mutex. This option allows the default to be changed to 2 to 64 concurrent threads.

--nanosleep N
    start N workers that each run pthreads that call nanosleep with random delays from 1 to 2↑18 nanoseconds. This should exercise the high resolution timers and scheduler.

--nanosleep-ops N
    stop the nanosleep stressor after N bogo nanosleep operations.

--nanosleep-threads N
    specify the number of concurrent pthreads to run per stressor. The default is 8 and the allowed range is 1 to 1024.

--netdev N
    start N workers that exercise various netdevice ioctl commands across all the available network devices. The ioctls exercised by this stressor are as follows: SIOCGIFCONF, SIOCGIFINDEX, SIOCGIFNAME, SIOCGIFFLAGS, SIOCGIFADDR, SIOCGIFNETMASK, SIOCGIFMETRIC, SIOCGIFMTU, SIOCGIFHWADDR, SIOCGIFMAP and SIOCGIFTXQLEN. See netdevice(7) for more details of these ioctl commands.

--netdev-ops N
    stop after N netdev bogo operations completed.

--netlink-proc N
    start N workers that spawn child processes and monitor fork/exec/exit process events via the proc netlink connector. Each event received is counted as a bogo op. This stressor can only be run on Linux and requires CAP_NET_ADMIN capability.

--netlink-proc-ops N
    stop the proc netlink connector stressors after N bogo ops.

--netlink-task N
    start N workers that collect task statistics via the netlink taskstats interface. This stressor can only be run on Linux and requires CAP_NET_ADMIN capability.

--netlink-task-ops N
    stop the taskstats netlink connector stressors after N bogo ops.

--nice N
    start N cpu consuming workers that exercise the available nice levels. Each iteration forks off a child process that runs through the all the nice levels running a busy loop for 0.1 seconds per level and then exits.

--nice-ops N
    stop after N nice bogo nice loops

--nop N
    start N workers that consume cpu cycles issuing no-op instructions. This stressor is available if the assembler supports the "nop" instruction.

--nop-instr INSTR
    use alternative nop instruction INSTR. For x86 CPUs INSTR can be one of nop, pause, nop2 (2 byte nop) through to nop15 (15 byte nop). For ARM CPUs, INSTR can be one of nop or yield. For PPC64 CPUs, INSTR can be one of nop, mdoio, mdoom or yield. For S390 CPUs, INSTR can be one of nop or nopr. For other processors, INSTR is only nop. The random INSTR option selects a randon mix of the available nop instructions. If the chosen INSTR generates an SIGILL signal, then the stressor falls back to the vanilla nop instruction.

--nop-ops N
    stop nop workers after N no-op bogo operations. Each bogo-operation is equivalent to 256 loops of 256 no-op instructions.

--null N
    start N workers writing to /dev/null.

--null-ops N
    stop null stress workers after N /dev/null bogo write operations.

--numa N
    start N workers that migrate stressors and a 4MB memory mapped buffer around all the available NUMA nodes. This uses migrate_pages(2) to move the stressors and mbind(2) and move_pages(2) to move the pages of the mapped buffer. After each move, the buffer is written to force activity over the bus which results cache misses. This test will only run on hardware with NUMA enabled and more than 1 NUMA node.

--numa-ops N
    stop NUMA stress workers after N bogo NUMA operations.

--oom-pipe N
    start N workers that create as many pipes as allowed and exercise expanding and shrinking the pipes from the largest pipe size down to a page size. Data is written into the pipes and read out again to fill the pipe buffers. With the --aggressive mode enabled the data is not read out when the pipes are shrunk, causing the kernel to OOM processes aggressively. Running many instances of this stressor will force kernel to OOM processes due to the many large pipe buffer allocations.

--oom-pipe-ops N
    stop after N bogo pipe expand/shrink operations.

--opcode N
    start N workers that fork off children that execute randomly generated executable code. This will generate issues such as illegal instructions, bus errors, segmentation faults, traps, floating point errors that are handled gracefully by the stressor.

--opcode-method [ inc | mixed | random | text ]
    select the opcode generation method. By default, random bytes are used to generate the executable code. This option allows one to select one of the three methods:
    Method | Description
    inc | use incrementing 32 bit opcode patterns from 0x00000000 to 0xfffffff inclusive.
    mixed | use a mix of incrementing 32 bit opcode patterns and random 32 bit opcode patterns that are also inverted, encoded with gray encoding and bit reversed.
    random | generate opcodes using random bytes from a mwc random generator.
    text | copies random chunks of code from the stress-ng text segment and randomly flips single bits in a random choice of 1/8th of the code.

--opcode-ops N
    stop after N attempts to execute illegal code.

-o N, --open N
    start N workers that perform open(2) and then close(2) operations on /dev/zero. The maximum opens at one time is system defined, so the test will run up to this maximum, or 65536 open file descriptors, which ever comes first.

--open-fd
    run a child process that scans /proc/$PID/fd and attempts to open the files that the stressor has opened. This exercises racing open/close operations on the proc interface.

--open-max N
    try to open a maximum of N files (or up to the maximum per-process open file system limit). The value can be the number of files or a percentage of the maximum per-process open file system limit.

--open-ops N
    stop the open stress workers after N bogo open operations.

--pagemove N
    start N workers that mmap a memory region (default 4 MB) and then shuffle pages to the virtual address of the previous page. Each page shuffle uses 3 mremap operations to move a page. This exercises page tables and Translation Lookaside Buffer (TLB) flushing.

--pagemove-bytes
    specify the size of the memory mapped region to be exercised. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--pagemove-mlock
    attempt to mlock mmap'd and mremap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--pagemove-ops N
    stop after N pagemove shuffling operations, where suffling all the pages in the mmap'd region is equivalent to 1 bogo-operation.

--pageswap N
    start N workers that exercise page swap in and swap out. Pages are allocated and paged out using madvise MADV_PAGEOUT. One the maximum per process number of mmaps are reached or 65536 pages are allocated the pages are read to page them back in and unmapped in reverse mapping order.

--pageswap-ops N
    stop after N page allocation bogo operations.

--pci N
    exercise PCI sysfs by running N workers that read data (and mmap/unmap PCI config or PCI resource files). Linux only. Running as root will allow config and resource mmappings to be read and exercises PCI I/O mapping.

--pci-ops N
    stop pci stress workers after N PCI subdirectory exercising operations.

--personality N
    start N workers that attempt to set personality and get all the available personality types (process execution domain types) via the personality(2) system call. (Linux only).

--personality-ops N
    stop personality stress workers after N bogo personality operations.

--peterson N
    start N workers that exercises mutex exclusion between two processes using shared memory with the Peterson Algorithm. Where possible this uses memory fencing and falls back to using GCC __sync_synchronize if they are not available. The stressors contain simple mutex and memory coherency sanity checks.

--peterson-ops N
    stop peterson workers after N mutex operations.

--physpage N
    start N workers that use /proc/self/pagemap and /proc/kpagecount to determine the physical page and page count of a virtual mapped page and a page that is shared among all the stressors. Linux only and requires the CAP_SYS_ADMIN capabilities.

--physpage-mtrr
    enable setting various memory type rage register (MTRR) types on physical pages (Linux and x86 only).

--physpage-ops N
    stop physpage stress workers after N bogo physical address lookups.

--pidfd N
    start N workers that exercise signal sending via the pidfd_send_signal system call. This stressor creates child processes and checks if they exist and can be stopped, restarted and killed using the pidfd_send_signal system call.

--pidfd-ops N
    stop pidfd stress workers after N child processes have been created, tested and killed with pidfd_send_signal.

--ping-sock N
    start N workers that send small randomized ICMP messages to the localhost across a range of ports (1024..65535) using a "ping" socket with an AF_INET domain, a SOCK_DGRAM socket type and an IPPROTO_ICMP protocol.

--ping-sock-ops N
    stop the ping-sock stress workers after N ICMP messages are sent.

-p N, --pipe N
    start N workers that perform large pipe writes and reads to exercise pipe I/O. This exercises memory write and reads as well as context switching. Each worker has two processes, a reader and a writer.

--pipe-data-size N
    specifies the size in bytes of each write to the pipe (range from 4 bytes to 4096 bytes). Setting a small data size will cause more writes to be buffered in the pipe, hence reducing the context switch rate between the pipe writer and pipe reader processes. Default size is the page size.

--pipe-ops N
    stop pipe stress workers after N bogo pipe write operations.

--pipe-size N
    specifies the size of the pipe in bytes (for systems that support the F_SETPIPE_SZ fcntl() command). Setting a small pipe size will cause the pipe to fill and block more frequently, hence increasing the context switch rate between the pipe writer and the pipe reader processes. As of version 0.15.11 the default size is 4096 bytes.

--pipeherd N
    start N workers that pass a 64 bit token counter to/from 100 child processes over a shared pipe. This forces a high context switch rate and can trigger a "thundering herd" of wakeups on processes that are blocked on pipe waits.

--pipeherd-ops N
    stop pipe stress workers after N bogo pipe write operations.

--pipeherd-yield
    force a scheduling yield after each write, this increases the context switch rate.

--pkey N
    start N workers that change memory protection using a protection key (pkey) and the pkey_mprotect call (Linux only). This will try to allocate a pkey and use this for the page protection, however, if this fails then the special pkey -1 will be used (and the kernel will use the normal mprotect mechanism instead). Various page protection mixes of read/write/exec/none will be cycled through on randomly chosen pre-allocated pages.

--pkey-ops N
    stop after N pkey_mprotect page protection cycles.

--plugin N
    start N workers that run user provided stressor functions loaded from a shared library. The shared library can contain one or more stressor functions prefixed with stress_ in their name. By default the plugin stressor will find all functions prefixed with stress_ in their name and exercise these one by one in a round-robin loop, but a specific stressor can be selected using the --plugin-method option. The stressor function takes no parameters and returns 0 for success and non-zero for failure (and will terminate the plugin stressor). Each time a stressor function is executed the bogo-op counter is incremented by one. The following example performs 10,000 nop instructions per bogo-op:

    int stress_example(void)
    {
            int i;
            for (i = 0; i < 10000; i++) {
                    __volatile__ __asm__("nop");
            }
            return 0;  /* Success */
    }

    and compile the source into a shared library as, for example:

    gcc -fpic -shared -o example.so example.c

    and run as using:

    stress-ng --plugin 1 --plugin-so ./example.so

--plugin-method function
    run a specific stressor function, specify the name without the leading stress_ prefix.

--plugin-ops N
    stop after N iterations of the user provided stressor function(s).

--plugin-so name
    specify the shared library containing the user provided stressor function(s).

-P N, --poll N
    start N workers that perform zero timeout polling via the poll(2), ppoll(2), select(2), pselect(2) and sleep(3) calls. This wastes system and user time doing nothing.

--poll-fds N
    specify the number of file descriptors to poll/ppoll/select/pselect on. The maximum number for select/pselect is limited by FD_SETSIZE and the upper maximum is also limited by the maximum number of pipe open descriptors allowed.

--poll-ops N
    stop poll stress workers after N bogo poll operations.

--prctl N
    start N workers that exercise the majority of the prctl(2) system call options. Each batch of prctl calls is performed inside a new child process to ensure the limit of prctl is contained inside a new process every time. Some prctl options are architecture specific, however, this stressor will exercise these even if they are not implemented.

--prctl-ops N
    stop prctl workers after N batches of prctl calls

--prefetch N
    start N workers that benchmark prefetch and non-prefetch reads of a L3 cache sized buffer. The buffer is read with loops of 8 × 64 bit reads per iteration. In the prefetch cases, data is prefetched ahead of the current read position by various sized offsets, from 64 bytes to 8K to find the best memory read throughput. The stressor reports the non-prefetch read rate and the best prefetched read rate. It also reports the prefetch offset and an estimate of the amount of time between the prefetch issue and the actual memory read operation. These statistics will vary from run-to-run due to system noise and CPU frequency scaling.

--prefetch-l3-size N
    specify the size of the l3 cache

--prefetch-method N
    select the prefetching method. Available methods are:
    Method | Description
    builtin | Use the __builtin_prefetch(3) function for prefetching. This is the default.
    builtinl0 | Use the __builtin_prefetch(3) function for prefetching, with a locality 0 hint.
    builtinl3 | Use the __builtin_prefetch(3) function for prefetching, with a locality 3 hint.
    dcbt | Use the ppc64 dcbt instruction to fetch data into the L1 cache (ppc64 only).
    dcbtst | Use the ppc64 dcbtst instruction to fetch data into the L1 cache (ppc64 only).
    prefetcht0 | Use the x86 prefetcht0 instruction to prefetch data into all levels of the cache hierarchy (x86 only).
    prefetcht1 | Use the x86 prefetcht1 instruction (temporal data with respect to first level cache) to prefetch data into level 2 cache and higher (x86 only).
    prefetcht2 | Use the x86 prefetcht2 instruction (temporal data with respect to second level cache) to prefetch data into level 2 cache and higher (x86 only).
    prefetchnta | Use the x86 prefetchnta instruction (non-temporal data with respect to all cache levels) into a location close to the processor, minimizing cache pollution (x86 only).

--prefetch-ops N
    stop prefetch stressors after N benchmark operations

--priv-instr N
    start N workers that exercise various architecture specific privileged instructions that cannot be executed by userspace programs. These instructions will be trapped and processed by SIGSEGV or SIGILL signal handlers.

--priv-instr-ops N
    stop priv-instr stressors after N rounds of executing privileged instructions.

--procfs N
    start N workers that read files from /proc and recursively read files from /proc/self (Linux only).

--procfs-ops N
    stop procfs reading after N bogo read operations. Note, since the number of entries may vary between kernels, this bogo ops metric is probably very misleading.

--pthread N
    start N workers that iteratively creates and terminates multiple pthreads (the default is 1024 pthreads per worker). In each iteration, each newly created pthread waits until the worker has created all the pthreads and then they all terminate together.

--pthread-max N
    create N pthreads per worker. If the product of the number of pthreads by the number of workers is greater than the soft limit of allowed pthreads then the maximum is re-adjusted down to the maximum allowed.

--pthread-ops N
    stop pthread workers after N bogo pthread create operations.

--ptrace N
    start N workers that fork and trace system calls of a child process using ptrace(2).

--ptrace-ops N
    stop ptracer workers after N bogo system calls are traced.

--pty N
    start N workers that repeatedly attempt to open pseudoterminals and perform various pty ioctls upon the ptys before closing them.

--pty-max N
    try to open a maximum of N pseudoterminals, the default is 65536. The allowed range of this setting is 8..65536.

--pty-ops N
    stop pty workers after N pty bogo operations.

-Q, --qsort N
    start N workers that sort 32 bit integers using qsort.

--qsort-method [ qsort-libc | qsort-bm ]
    select either the libc implementation of qsort or the J. L. Bentley and M. D. McIlroy implementation of qsort. The default is the libc implementation.

--qsort-ops N
    stop qsort stress workers after N bogo qsorts.

--qsort-size N
    specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--quota N
    start N workers that exercise the Q_GETQUOTA, Q_GETFMT, Q_GETINFO, Q_GETSTATS and Q_SYNC quotactl(2) commands on all the available mounted block based file systems. Requires CAP_SYS_ADMIN capability to run.

--quota-ops N
    stop quota stress workers after N bogo quotactl operations.

--race-sched N
    start N workers that exercise rapid changing CPU affinity child processes both from the controlling stressor and by the child processes. Child processes are created and terminated rapidly with the aim to create race conditions where affinity changing occurs during process run states.

--race-sched-method [ all | next | prev | rand | randinc | syncnext | syncprev ]
    Select the method moving a process to a specific CPU. Available methods are described as follows:
    Method | Description
    all | iterate over all the race-sched methods as listed below:
    next | move a process to the next CPU, wrap around to zero when maximum CPU is reached.
    prev | move a process to the previous CPU, wrap around to the maximum CPU when the first CPU is reached.
    rand | move a process to any randomly chosen CPU.
    randinc | move a process to the current CPU + a randomly chosen value 1..4, modulo the number of CPUs.
    syncnext | move synchronously all the race-sched stressor processes to the next CPU every second; this loads just 1 CPU at a time in a round-robin method.
    syncprev | move synchronously all the race-sched stressor processes to the previous CPU every second; this loads just 1 CPU at a time in a round-robin method.

--race-sched-ops N
    stop after N process creation bogo-operations.

--radixsort N
    start N workers that sort random 8 byte strings using radixsort.

--radixsort-ops N
    stop radixsort stress workers after N bogo radixsorts.

--radixsort-size N
    specify number of strings to sort, default is 262144 (256 × 1024).

--ramfs N
    start N workers mounting a memory based file system using ramfs and tmpfs (Linux only). This alternates between mounting and umounting a ramfs or tmpfs file system using the traditional mount(2) and umount(2) system call as well as the newer Linux 5.2 fsopen(2), fsmount(2), fsconfig(2) and move_mount(2) system calls if they are available. The default ram file system size is 2MB.

--ramfs-fill
    fill ramfs with zero'd data using fallocate(2) if it is available or multiple calls to write(2) if not.

--ramfs-ops N
    stop after N ramfs mount operations.

--ramfs-size N
    set the ramfs size (must be multiples of the page size).

--rawdev N
    start N workers that read the underlying raw drive device using direct IO reads. The device (with minor number 0) that stores the current working directory is the raw device to be read by the stressor. The read size is exactly the size of the underlying device block size. By default, this stressor will exercise all the of the rawdev methods (see the --rawdev-method option). This is a Linux only stressor and requires root privilege to be able to read the raw device.

--rawdev-method method
    Available rawdev stress methods are described as follows:
    Method | Description
    all | iterate over all the rawdev stress methods as listed below:
    sweep | repeatedly read across the raw device from the 0th block to the end block in steps of the number of blocks on the device / 128 and back to the start again.
    wiggle | repeatedly read across the raw device in 128 evenly steps with each step reading 1024 blocks backwards from each step.
    ends | repeatedly read the first and last 128 start and end blocks of the raw device alternating from start of the device to the end of the device.
    random | repeatedly read 256 random blocks
    burst | repeatedly read 256 sequential blocks starting from a random block on the raw device.

--rawdev-ops N
    stop the rawdev stress workers after N raw device read bogo operations.

--randlist N
    start N workers that creates a list of objects in randomized memory order and traverses the list setting and reading the objects. This is designed to exerise memory and cache thrashing. Normally the objects are allocated on the heap, however for objects of page size or larger there is a 1 in 16 chance of objects being allocated using shared anonymous memory mapping to mix up the address spaces of the allocations to create more TLB thrashing.

--randist-compact
    Allocate all the list objects using one large heap allocation and divide this up for all the list objects. This removes the overhead of the heap keeping track of each list object, hence uses less memory.

--randlist-items N
    Allocate N items on the list. By default, 100,000 items are allocated.

--randlist-ops N
    stop randlist workers after N list traversals

--randlist-size N
    Allocate each item to be N bytes in size. By default, the size is 64 bytes of data payload plus the list handling pointer overhead.

--rawsock N
    start N workers that send and receive packet data using raw sockets on the localhost. Requires CAP_NET_RAW to run.

--rawsock-ops N
    stop rawsock workers after N packets are received.

--rawsock-port P
    start at socket port P. For N rawsock worker processes, ports P to P - 1 are used.

--rawpkt N
    start N workers that sends and receives ethernet packets using raw packets on the localhost via the loopback device. Requires CAP_NET_RAW to run.

--rawpkt-ops N
    stop rawpkt workers after N packets from the sender process are received.

--rawpkt-port N
    start at port P. For N rawpkt worker processes, ports P to (P * 4) - 1 are used. The default starting port is port 14000.

--rawpkt-rxring N
    setup raw packets with RX ring with N number of blocks, this selects TPACKET_V. N must be one of 1, 2, 4, 8 or 16.

--rawudp N
    start N workers that send and receive UDP packets using raw sockets on the localhost. Requires CAP_NET_RAW to run.

--rawudp-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--rawudp-ops N
    stop rawudp workers after N packets are received.

--rawudp-port N
    start at port P. For N rawudp worker processes, ports P to (P * 4) - 1 are used. The default starting port is port 13000.

--rdrand N
    start N workers that read a random number from an on-chip random number generator This uses the rdrand instruction on Intel x86 processors or the darn instruction on Power9 processors.

--rdrand-ops N
    stop rdrand stress workers after N bogo rdrand operations (1 bogo op = 2048 random bits successfully read).

--rdrand-seed
    use rdseed instead of rdrand (x86 only).

--readahead N
    start N workers that randomly seek and perform 4096 byte read/write I/O operations on a file with readahead. The default file size is 64 MB. Readaheads and reads are batched into 16 readaheads and then 16 reads.

--readahead-bytes N
    set the size of readahead file, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--readahead-ops N
    stop readahead stress workers after N bogo read operations.

--reboot N
    start N workers that exercise the reboot(2) system call. When possible, it will create a process in a PID namespace and perform a reboot power off command that should shutdown the process. Also, the stressor exercises invalid reboot magic values and invalid reboots when there are insufficient privileges that will not actually reboot the system.

--reboot-ops N
    stop the reboot stress workers after N bogo reboot cycles.

--regs N
    start N workers that shuffle data around the CPU registers exercising register move instructions. Each bogo-op represents 1000 calls of a shuffling function that shuffles the registers 32 times. Only implemented for the GCC compiler since this requires register annotations and optimization level 0 to compile appropriately.

--regs-ops N
    stop regs stressors after N bogo operations.

--remap N
    start N workers that map 512 pages and re-order these pages using the deprecated system call remap_file_pages(2). Several page re-orderings are exercised: forward, reverse, random and many pages to 1 page.

--remap-mlock
    attempt to mlock mmap'd huge pages into memory causing more memory pressure by preventing pages from swapped out.

--remap-ops N
    stop after N remapping bogo operations.

--remap-pages N
    specify number of pages to remap, must be a power of 2, default is 512 pages.

-R N, --rename N
    start N workers that each create a file and then repeatedly rename it.

--rename-ops N
    stop rename stress workers after N bogo rename operations.

--resched N
    start N workers that exercise process rescheduling. Each stressor spawns a child process for each of the positive nice levels and iterates over the nice levels from 0 to the lowest priority level (highest nice value). For each of the nice levels 1024 iterations over 3 non-real time scheduling polices SCHED_OTHER, SCHED_BATCH and SCHED_IDLE are set and a sched_yield occurs to force heavy rescheduling activity. When the -v verbose option is used the distribution of the number of yields across the nice levels is printed for the first stressor out of the N stressors.

--resched-ops N
    stop after N rescheduling sched_yield calls.

--resources N
    start N workers that consume various system resources. Each worker will spawn 1024 child processes that iterate 1024 times consuming shared memory, heap, stack, temporary files and various file descriptors (eventfds, memoryfds, userfaultfds, pipes and sockets).

--resources-mlock
    attempt to mlock mmap'd pages into memory causing more memory pressure by preventing pages from swapped out.

--resources-ops N
    stop after N resource child forks.

--revio N
    start N workers continually writing in reverse position order to temporary files. The default mode is to stress test reverse position ordered writes with randomly sized sparse holes between each write. With the --aggressive option enabled without any --revio-opts options the revio stressor will work through all the --revio-opt options one by one to cover a range of I/O options.

--revio-bytes N
    write N bytes for each revio process, the default is 1 GB. One can specify the size as % of free space on the file system or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--revio-opts list
    specify various stress test options as a comma separated list. Options are the same as --hdd-opts but without the iovec option.

--revio-ops N
    stop revio stress workers after N bogo operations.

--revio-write-size N
    specify size of each write in bytes. Size can be from 1 byte to 4MB.

--ring-pipe N
    start N workers that move data around a ring of pipes using poll to detect when data is ready to copy. By default, 256 pipes are used with two 4096 byte items of data being copied around the ring of pipes. Data is copied using read and write system calls. If the splice system call is available then one can use splice to use more efficient in-kernel data passing instead of buffer copying.

--ring-pipe-num N
    specify the number of pipes to use. Ranges from 4 to 262144, default is 256.

--ring-pipe-ops N
    stop after N pipe data transfers.

--ring-pipe-size N
    specify the size of data being copied in bytes. Ranges from 1 to 4096, default is 4096.

--ring-pipe-splice
    enable splice to move data between pipes (only if splice() is available).

--rlimit N
    start N workers that exceed CPU and file size resource imits, generating SIGXCPU and SIGXFSZ signals.

--rlimit-ops N
    stop after N bogo resource limited SIGXCPU and SIGXFSZ signals have been caught.

--rmap N
    start N workers that exercise the VM reverse-mapping. This creates 16 processes per worker that write/read multiple file-backed memory mappings. There are 64 lots of 4 page mappings made onto the file, with each mapping overlapping the previous by 3 pages and at least 1 page of non-mapped memory between each of the mappings. Data is synchronously msync'd to the file 1 in every 256 iterations in a random manner.

--rmap-ops N
    stop after N bogo rmap memory writes/reads.

--rotate N
    start N workers that exercise 1 bit rotates left and right of unsigned integer variables. The default will rotate four 8, 16, 32, 64 (and if supported 128) bit values 10000 times in a loop per bogo-op.

--rotate-method M
    specify the method of rotation to use. The 'all' method uses all the methods and is the default.
    Method | Description
    all | exercise with all the rotate stressor methods (see below):
    rol8 | 8 bit unsigned rotate left by 1 bit
    ror8 | 8 bit unsigned rotate right by 1 bit
    rol16 | 16 bit unsigned rotate left by 1 bit
    ror16 | 16 bit unsigned rotate right by 1 bit
    rol32 | 32 bit unsigned rotate left by 1 bit
    ror32 | 32 bit unsigned rotate right by 1 bit
    rol64 | 64 bit unsigned rotate left by 1 bit
    ror64 | 64 bit unsigned rotate right by 1 bit
    rol128 | 128 bit unsigned rotate left by 1 bit
    ror128 | 128 bit unsigned rotate right by 1 bit

--rotate-ops N
    stop after N bogo rotate operations.

--rseq N
    start N workers that exercise restartable sequences via the rseq(2) system call. This loops over a long duration critical section that is likely to be interrupted. A rseq abort handler keeps count of the number of interruptions and a SIGSEV handler also tracks any failed rseq aborts that can occur if there is a mismatch in a rseq check signature. Linux only.

--rseq-ops N
    stop after N bogo rseq operations. Each bogo rseq operation is equivalent to 10000 iterations over a long duration rseq handled critical section.

--rtc N
    start N workers that exercise the real time clock (RTC) interfaces via /dev/rtc and /sys/class/rtc/rtc0. No destructive writes (modifications) are performed on the RTC. This is a Linux only stressor.

--rtc-ops N
    stop after N bogo RTC interface accesses.

--schedpolicy N
    start N workers that set the worker to various available scheduling policies out of SCHED_OTHER, SCHED_BATCH, SCHED_IDLE, SCHED_FIFO, SCHED_RR and SCHED_DEADLINE. For the real time scheduling policies a random sched priority is selected between the minimum and maximum scheduling priority settings.

--schedpolicy-ops N
    stop after N bogo scheduling policy changes.

--schedpolicy-rand
    Select scheduling policy randomly so that the new policy is always different to the previous policy. The default is to work through the scheduling policies sequentially.

--sctp N
    start N workers that perform network sctp stress activity using the Stream Control Transmission Protocol (SCTP). This involves client/server processes performing rapid connect, send/receives and disconnects on the local host.

--sctp-domain D
    specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are supported.

--sctp-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--sctp-ops N
    stop sctp workers after N bogo operations.

--sctp-port P
    start at sctp port P. For N sctp worker processes, ports P to (P * 4) - 1 are used for ipv4, ipv6 domains and ports P to P - 1 are used for the unix domain.

--sctp-sched [ fcfs | prio | rr ]
    specify SCTP scheduler, one of fcfs (default), prio (priority) or rr (round-robin).

--seal N
    start N workers that exercise the fcntl(2) SEAL commands on a small anonymous file created using memfd_create(2). After each SEAL command is issued the stressor also sanity checks if the seal operation has sealed the file correctly. (Linux only).

--seal-ops N
    stop after N bogo seal operations.

--seccomp N
    start N workers that exercise Secure Computing system call filtering. Each worker creates child processes that write a short message to /dev/null and then exits. 2% of the child processes have a seccomp filter that disallows the write system call and hence it is killed by seccomp with a SIGSYS. Note that this stressor can generate many audit log messages each time the child is killed. Requires CAP_SYS_ADMIN to run.

--seccomp-ops N
    stop seccomp stress workers after N seccomp filter tests.

--secretmem N
    start N workers that mmap pages using file mapping off a memfd_secret file descriptor. Each stress loop iteration will expand the mappable region by 3 pages using ftruncate and mmap and touches the pages. The pages are then fragmented by unmapping the middle page and then umapping the first and last pages. This tries to force page fragmentation and also trigger out of memory (OOM) kills of the stressor when the secret memory is exhausted. Note this is a Linux 5.11+ only stressor and the kernel needs to be booted with "secretmem=" option to allocate a secret memory reservation.

--secretmem-ops N
    stop secretmem stress workers after N stress loop iterations.

--seek N
    start N workers that randomly seeks and performs 512 byte read/write I/O operations on a file. The default file size is 16 GB.

--seek-ops N
    stop seek stress workers after N bogo seek operations.

--seek-punch
    punch randomly located 8K holes into the file to cause more extents to force a more demanding seek stressor, (Linux only).

--seek-size N
    specify the size of the file in bytes. Small file sizes allow the I/O to occur in the cache, causing greater CPU load. Large file sizes force more I/O operations to drive causing more wait time and more I/O on the drive. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--sem N
    start N workers that perform POSIX semaphore wait and post operations. By default, a parent and 4 children are started per worker to provide some contention on the semaphore. This stresses fast semaphore operations and produces rapid context switching.

--sem-ops N
    stop semaphore stress workers after N bogo semaphore operations.

--sem-procs N
    start N child workers per worker to provide contention on the semaphore, the default is 4 and a maximum of 64 are allowed.

--sem-sysv N
    start N workers that perform System V semaphore wait and post operations. By default, a parent and 4 children are started per worker to provide some contention on the semaphore. This stresses fast semaphore operations and produces rapid context switching.

--sem-sysv-ops N
    stop semaphore stress workers after N bogo System V semaphore operations.

--sem-sysv-procs N
    start N child processes per worker to provide contention on the System V semaphore, the default is 4 and a maximum of 64 are allowed.

--sendfile N
    start N workers that send an empty file to /dev/null. This operation spends nearly all the time in the kernel. The default sendfile size is 4MB. The sendfile options are for Linux only.

--sendfile-ops N
    stop sendfile workers after N sendfile bogo operations.

--sendfile-size S
    specify the size to be copied with each sendfile call. The default size is 4MB. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--session N
    start N workers that create child and grandchild processes that set and get their session ids. 25% of the grandchild processes are not waited for by the child to create orphaned sessions that need to be reaped by init.

--session-ops N
    stop session workers after N child processes are spawned and reaped.

--set N
    start N workers that call system calls that try to set data in the kernel, currently these are: setgid, sethostname, setpgid, setpgrp, setuid, setgroups, setreuid, setregid, setresuid, setresgid and setrlimit. Some of these system calls are OS specific.

--set-ops N
    stop set workers after N bogo set operations.

--shellsort N
    start N workers that sort 32 bit integers using shellsort.

--shellsort-ops N
    stop shellsort stress workers after N bogo shellsorts.

--shellsort-size N
    specify number of 32 bit integers to sort, default is 262144 (256 × 1024).

--shm N
    start N workers that open and allocate shared memory objects using the POSIX shared memory interfaces. By default, the test will repeatedly create and destroy 32 shared memory objects, each of which is 8MB in size.

--shm-bytes N
    specify the size of the POSIX shared memory objects to be created. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--shm-mlock
    attempt to mlock shared memory objects into memory causing more memory pressure by preventing pages from swapped out.

--shm-objs N
    specify the number of shared memory objects to be created.

--shm-ops N
    stop after N POSIX shared memory create and destroy bogo operations are complete.

--shm-sysv N
    start N workers that allocate shared memory using the System V shared memory interface. By default, the test will repeatedly create and destroy 8 shared memory segments, each of which is 8MB in size.

--shm-sysv-bytes N
    specify the size of the shared memory segment to be created. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--shm-sysv-mlock
    attempt to mlock shared memory segment into memory causing more memory pressure by preventing pages from swapped out.

--shm-sysv-ops N
    stop after N shared memory create and destroy bogo operations are complete.

--shm-sysv-segs N
    specify the number of shared memory segments to be created. The default is 8 segments.

--sigabrt N
    start N workers that create children that are killed by SIGABRT signals or by calling abort(3).

--sigabrt-ops N
    stop the sigabrt workers after N SIGABRT signals are successfully handled.

--sigchld N
    start N workers that create children to generate SIGCHLD signals. This exercises children that exit (CLD_EXITED), get killed (CLD_KILLED), get stopped (CLD_STOPPED) or continued (CLD_CONTINUED).

--sigchld-ops N
    stop the sigchld workers after N SIGCHLD signals are successfully handled.

--sigfd N
    start N workers that generate SIGRT signals and are handled by reads by a child process using a file descriptor set up using signalfd(2). (Linux only). This will generate a heavy context switch load when all CPUs are fully loaded.

--sigfd-ops
    stop sigfd workers after N bogo SIGUSR1 signals are sent.

--sigfpe N
    start N workers that rapidly cause division by zero SIGFPE faults.

--sigfpe-ops N
    stop sigfpe stress workers after N bogo SIGFPE faults.

--sigio N
    start N workers that read data from a child process via a pipe and generate SIGIO signals. This exercises asynchronous I/O via SIGIO.

--sigio-ops N
    stop sigio stress workers after handling N SIGIO signals.

--signal N
    start N workers that exercise the signal system call three different signal handlers, SIG_IGN (ignore), a SIGCHLD handler and SIG_DFL (default action). For the SIGCHLD handler, the stressor sends itself a SIGCHLD signal and checks if it has been handled. For other handlers, the stressor checks that the SIGCHLD handler has not been called. This stress test calls the signal system call directly when possible and will try to avoid the C library attempt to replace signal with the more modern sigaction system call.

--signal-ops N
    stop signal stress workers after N rounds of signal handler setting.

--signest N
    start N workers that exercise nested signal handling. A signal is raised and inside the signal handler a different signal is raised, working through a list of signals to exercise. An alternative signal stack is used that is large enough to handle all the nested signal calls. The -v option will log the approximate size of the stack required and the average stack size per nested call.

--signest-ops N
    stop after handling N nested signals.

--sigpending N
    start N workers that check if SIGUSR1 signals are pending. This stressor masks SIGUSR1, generates a SIGUSR1 signal and uses sigpending(2) to see if the signal is pending. Then it unmasks the signal and checks if the signal is no longer pending.

--sigpending-ops N
    stop sigpending stress workers after N bogo sigpending pending/unpending checks.

--sigpipe N
    start N workers that repeatedly spawn off child process that exits before a parent can complete a pipe write, causing a SIGPIPE signal. The child process is either spawned using clone(2) if it is available or use the slower fork(2) instead.

--sigpipe-ops N
    stop N workers after N SIGPIPE signals have been caught and handled.

--sigq N
    start N workers that rapidly send SIGUSR1 signals using sigqueue(3) to child processes that wait for the signal via sigwaitinfo(2).

--sigq-ops N
    stop sigq stress workers after N bogo signal send operations.

--sigrt N
    start N workers that each create child processes to handle SIGRTMIN to SIGRMAX real time signals. The parent sends each child process a RT signal via siqueue(2) and the child process waits for this via sigwaitinfo(2). When the child receives the signal it then sends a RT signal to one of the other child processes also via sigqueue(2).

--sigrt-ops N
    stop sigrt stress workers after N bogo sigqueue signal send operations.

--sigsegv N
    start N workers that rapidly create and catch segmentation faults generated via illegal memory access, illegal vdso system calls, illegal port reads, illegal interrupts or access to x86 time stamp counter.

--sigsegv-ops N
    stop sigsegv stress workers after N bogo segmentation faults.

--sigsuspend N
    start N workers that each spawn off 4 child processes that wait for a SIGUSR1 signal from the parent using sigsuspend(2). The parent sends SIGUSR1 signals to each child in rapid succession. Each sigsuspend wakeup is counted as one bogo operation.

--sigsuspend-ops N
    stop sigsuspend stress workers after N bogo sigsuspend wakeups.

--sigtrap N
    start N workers that exercise the SIGTRAP signal. For systems that support SIGTRAP, the signal is generated using raise(SIGTRAP). Only x86 Linux systems the SIGTRAP is also generated by an int 3 instruction.

--sigtrap-ops N
    stop sigtrap stress workers after N SIGTRAPs have been handled.

--skiplist N
    start N workers that store and then search for integers using a skiplist. By default, 65536 integers are added and searched. This is a useful method to exercise random access of memory and processor cache.

--skiplist-ops N
    stop the skiplist worker after N skiplist store and search cycles are completed.

--skiplist-size N
    specify the size (number of integers) to store and search in the skiplist. Size can be from 1K to 4M.

--sleep N
    start N workers that spawn off multiple threads that each perform multiple sleeps of ranges 1us to 0.1s. This creates multiple context switches and timer interrupts.

--sleep-max P
    start P threads per worker. The default is 1024, the maximum allowed is 30000.

--sleep-ops N
    stop after N sleep bogo operations.

--smi N
    start N workers that attempt to generate system management interrupts (SMIs) into the x86 ring -2 system management mode (SMM) by exercising the advanced power management (APM) port 0xb2. This requires the --pathological option and root privilege and is only implemented on x86 Linux platforms. This probably does not work in a virtualized environment. The stressor will attempt to determine the time stolen by SMIs with some naïve benchmarking.

--smi-ops N
    stop after N attempts to trigger the SMI.

-S N, --sock N
    start N workers that perform various socket stress activity. This involves a pair of client/server processes performing rapid connect, send and receives and disconnects on the local host.

--sock-domain D
    specify the domain to use, the default is ipv4. Currently ipv4, ipv6 and unix are supported.

--sock-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--sock-nodelay
    This disables the TCP Nagle algorithm, so data segments are always sent as soon as possible. This stops data from being buffered before being transmitted, hence resulting in poorer network utilisation and more context switches between the sender and receiver.

--sock-ops N
    stop socket stress workers after N bogo operations.

--sock-opts [ random | send | sendmsg | sendmmsg ]
    by default, messages are sent using send(2). This option allows one to specify the sending method using send(2), sendmsg(2), sendmmsg(2) or a random selection of one of these 3 on each iteration. Note that sendmmsg is only available for Linux systems that support this system call.

--sock-port P
    start at socket port P. For N socket worker processes, ports P to P - 1 are used.

--sock-protocol P
    Use the specified protocol P, default is tcp. Options are tcp and mptcp (if supported by the operating system).

--sock-type [ stream | seqpacket ]
    specify the socket type to use. The default type is stream. seqpacket currently only works for the unix socket domain.

--sock-zerocopy
    enable zerocopy for send and recv calls if the MSG_ZEROCOPY is supported.

--sockabuse N
    start N workers that abuse a socket file descriptor with various file based system that don't normally act on sockets. The kernel should handle these illegal and unexpected calls gracefully.

--sockabuse-ops N
    stop after N iterations of the socket abusing stressor loop.

--sockabuse-port P
    start at socket port P. For N sockabuse worker processes, ports P to P - 1 are used.

--sockdiag N
    start N workers that exercise the Linux sock_diag netlink socket diagnostics (Linux only). This currently requests diagnostics using UDIAG_SHOW_NAME, UDIAG_SHOW_VFS, UDIAG_SHOW_PEER, UDIAG_SHOW_ICONS, UDIAG_SHOW_RQLEN and UDIAG_SHOW_MEMINFO for the AF_UNIX family of socket connections.

--sockdiag-ops N
    stop after receiving N sock_diag diagnostic messages.

--sockfd N
    start N workers that pass file descriptors over a UNIX domain socket using the CMSG(3) ancillary data mechanism. For each worker, pair of client/server processes are created, the server opens as many file descriptors on /dev/null as possible and passing these over the socket to a client that reads these from the CMSG data and immediately closes the files.

--sockfd-ops N
    stop sockfd stress workers after N bogo operations.

--sockfd-port P
    start at socket port P. For N socket worker processes, ports P to P - 1 are used.

--sockmany N
    start N workers that use a client process to attempt to open as many as 100000 TCP/IP socket connections to a server on port 10000.

--sockmany-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--sockmany-ops N
    stop after N connections.

--sockmany-port P
    start at socket port P. For N sockmany worker processes, ports P to P - 1 are used.

--sockpair N
    start N workers that perform socket pair I/O read/writes. This involves a pair of client/server processes performing randomly sized socket I/O operations.

--sockpair-ops N
    stop socket pair stress workers after N bogo operations.

--softlockup N
    start N workers that flip between with the "real-time" SCHED_FIO and SCHED_RR scheduling policies at the highest priority to force softlockups. This can only be run with CAP_SYS_NICE capability and for best results the number of stressors should be at least the number of online CPUs. Once running, this is practically impossible to stop and it will force softlockup issues and may trigger watchdog timeout reboots.

--softlockup-ops N
    stop softlockup stress workers after N bogo scheduler policy changes.

--sparsematrix N
    start N workers that exercise 3 different sparse matrix implementations based on hashing, Judy array (for 64 bit systems), 2-d circular linked-lists, memory mapped 2-d matrix (non-sparse), quick hashing (on preallocated nodes) and red-black tree. The sparse matrix is populated with values, random values potentially non-existing values are read, known existing values are read and known existing values are marked as zero. This default 500 × 500 sparse matrix is used and 5000 items are put into the sparse matrix making it 2% utilized.

--sparsematrix-items N
    populate the sparse matrix with N items. If N is greater than the number of elements in the sparse matrix than N will be capped to create at 100% full sparse matrix.

--sparsematrix-method [ all | hash | hashjudy | judy | list | mmap | qhash | rb ]
    specify the type of sparse matrix implementation to use. The 'all' method uses all the methods and is the default.
    Method | Description
    all | exercise with all the sparsematrix stressor methods (see below):
    hash | use a hash table and allocate nodes on the heap for each unique value at a (x, y) matrix position.
    hashjudy | use a hash table for x coordinates and a Judy array for y coordinates for values at a (x, y) matrix position.
    judy | use a Judy array with a unique 1-to-1 mapping of (x, y) matrix position into the array.
    list | use a circular linked-list for sparse y positions each with circular linked-lists for sparse x positions for the (x, y) matrix coordinates.
    mmap | use a non-sparse mmap the entire 2-d matrix space. Only (x, y) matrix positions that are referenced will get physically mapped. Note that large sparse matrices cannot be mmap'd due to lack of virtual address limitations, and too many referenced pages can trigger the out of memory killer on Linux.
    qhash | use a hash table with pre-allocated nodes for each unique value. This is a quick hash table implementation, nodes are not allocated each time with calloc and are allocated from a pre-allocated pool leading to quicker hash table performance than the hash method.
    rb | use a red-black balanced tree using one tree node for each unique value at a (x, y) matrix position.
    splay | use a splay tree using one tree node for each unique value at a (x, y) matrix position.

--sparsematrix-ops N
    stop after N sparsematrix test iterations.

--sparsematrix-size N
    use a N × N sized sparse matrix

--spawn N
    start N workers continually spawn children using posix_spawn(3) that exec stress-ng and then exit almost immediately. Currently Linux only.

--spawn-ops N
    stop spawn stress workers after N bogo spawns.

--splice N
    move data from /dev/zero to /dev/null through a pipe without any copying between kernel address space and user address space using splice(2). This is only available for Linux.

--splice-bytes N
    transfer N bytes per splice call, the default is 64K. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--splice-ops N
    stop after N bogo splice operations.

--stack N
    start N workers that rapidly cause and catch stack overflows by use of large recursive stack allocations. Much like the brk stressor, this can eat up pages rapidly and may trigger the kernel OOM killer on the process, however, the killed stressor is respawned again by a monitoring parent process.

--stack-fill
    the default action is to touch the lowest page on each stack allocation. This option touches all the pages by filling the new stack allocation with zeros which forces physical pages to be allocated and hence is more aggressive.

--stack-mlock
    attempt to mlock stack pages into memory causing more memory pressure by preventing pages from swapped out.

--stack-ops N
    stop stack stress workers after N bogo stack overflows.

--stack-pageout
    force stack pages out to swap (available when madvise(2) supports MADV_PAGEOUT).

--stack-unmap
    unmap a single page in the middle of a large buffer allocated on the stack on each stack allocation. This forces the stack mapping into multiple separate allocation mappings.

--stackmmap N
    start N workers that use a 2MB stack that is memory mapped onto a temporary file. A recursive function works down the stack and flushes dirty stack pages back to the memory mapped file using msync(2) until the end of the stack is reached (stack overflow). This exercises dirty page and stack exception handling.

--stackmmap-ops N
    stop workers after N stack overflows have occurred.

--str N
    start N workers that exercise various libc string functions on random strings.

--str-method strfunc
    select a specific libc string function to stress. Available string functions to stress are: all, index, rindex, strcasecmp, strcat, strchr, strcoll, strcmp, strcpy, strlen, strncasecmp, strncat, strncmp, strrchr and strxfrm. See string(3) for more information on these string functions. The 'all' method is the default and will exercise all the string methods.

--str-ops N
    stop after N bogo string operations.

--stream N
    start N workers exercising a memory bandwidth stressor very loosely based on the STREAM "Sustainable Memory Bandwidth in High Performance Computers" benchmarking tool by John D. McCalpin, Ph.D. This stressor allocates buffers that are at least 4 times the size of the CPU L2 cache and continually performs rounds of following computations on large arrays of double precision floating point numbers:
    Operation | Description
    copy | c[i] = a[i]
    scale | b[i] = scalar * c[i]
    add | c[i] = a[i] + b[i]
    triad | a[i] = b[i] + (c[i] * scalar)

    Since this is loosely based on a variant of the STREAM benchmark code, DO NOT submit results based on this as it is intended to in stress-ng just to stress memory and compute and NOT intended for STREAM accurate tuned or non-tuned benchmarking whatsoever. Use the official STREAM benchmarking tool if you desire accurate and standardised STREAM benchmarks.

    The stressor calculates the memory read rate, memory write rate and floating point operations rate. These will differ from the maximum theoretical read/write/compute rates because of loop overheads and the use of volatile pointers to ensure the compiler does not optimize out stores.

--stream-index N
    specify number of stream indices used to index into the data arrays a, b and c. This adds indirection into the data lookup by using randomly shuffled indexing into the three data arrays. Level 0 (no indexing) is the default, and 3 is where all 3 arrays are indexed via 3 different randomly shuffled indexes. The higher the index setting the more impact this has on L1, L2 and L3 caching and hence forces higher memory read/write latencies.

--stream-l3-size N
    Specify the CPU Level 3 cache size in bytes. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. If the L3 cache size is not provided, then stress-ng will attempt to determine the cache size, and failing this, will default the size to 4MB.

--stream-mlock
    attempt to mlock the stream buffers into memory to prevent them from being swapped out.

--stream-madvise [ hugepage | nohugepage | normal ]
    Specify the madvise options used on the memory mapped buffer used in the stream stressor. Non-linux systems will only have the 'normal' madvise advice. The default is 'normal'.

--stream-ops N
    stop after N stream bogo operations, where a bogo operation is one round of copy, scale, add and triad operations.

--swap N
    start N workers that add and remove small randomly sizes swap partitions (Linux only). Note that if too many swap partitions are added then the stressors may exit with exit code 3 (not enough resources). Requires CAP_SYS_ADMIN to run.

--swap-ops N
    stop the swap workers after N swapon/swapoff iterations.

-s N, --switch N
    start N workers that force context switching between two mutually blocking/unblocking tied processes. By default message passing over a pipe is used, but different methods are available.

--switch-freq F
    run the context switching at the frequency of F context switches per second. Note that the specified switch rate may not be achieved because of CPU speed and memory bandwidth limitations.

--switch-method [ mq | pipe | sem-sysv ]
    select the preferred context switch block/run synchronization method, these are as follows:
    Method | Description
    mq | use posix message queue with a 1 item size. Messages are passed between a sender and receiver process.
    pipe | single character messages are passed down a single character sized pipe between a sender and receiver process.
    sem-sysv | a SYSV semaphore is used to block/run two processes.

--switch-ops N
    stop context switching workers after N bogo operations.

--symlink N
    start N workers creating and removing symbolic links.

--symlink-ops N
    stop symlink stress workers after N bogo operations.

--symlink-sync
    sync dirty data and metadata to disk.

--sync-file N
    start N workers that perform a range of data syncs across a file using sync_file_range(2). Three mixes of syncs are performed, from start to the end of the file, from end of the file to the start, and a random mix. A random selection of valid sync types are used, covering the SYNC_FILE_RANGE_WAIT_BEFORE, SYNC_FILE_RANGE_WRITE and SYNC_FILE_RANGE_WAIT_AFTER flag bits.

--sync-file-bytes N
    specify the size of the file to be sync'd. One can specify the size as % of free space on the file system in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--sync-file-ops N
    stop sync-file workers after N bogo sync operations.

--syncload N
    start N workers that produce sporadic short lived loads synchronized across N stressor processes. By default repeated cycles of 125ms busy load followed by 62.5ms sleep occur across all the workers in step to create bursts of load to exercise C state transitions and CPU frequency scaling. The busy load and sleeps have +/-10% jitter added to try exercising scheduling patterns.

--syncload-msbusy M
    specify the busy load duration in milliseconds.

--syncload-mssleep M
    specify the sleep duration in milliseconds.

--syncload-ops N
    stop syncload workers after N load/sleep cycles.

--sysbadaddr N
    start N workers that pass bad addresses to system calls to exercise bad address and fault handling. The addresses used are null pointers, read only pages, write only pages, unmapped addresses, text only pages, unaligned addresses and top of memory addresses.

--sysbadaddr-ops N
    stop the sysbadaddr stressors after N bogo system calls.

--syscall N
    start N workers that exercise a range of available system calls. System calls that fail due to lack of capabilities or errors are ignored. The stressor will try to maximize the rate of system calls being executed based the entire time taken to setup, run and cleanup after each system call.

--syscall-method method
    select the choice of system calls to executed based on the fasted test duration times. Note that this includes the time to setup, execute the system call and cleanup afterwards. The available methods are as follows:
    Method | Description
    all | select all the available system calls
    fast10 | select the fastest 10% system call tests
    fast25 | select the fastest 25% system call tests
    fast50 | select the fastest 50% system call tests
    fast75 | select the fastest 75% system call tests
    fast90 | select the fastest 90% system call tests
    geomean1 | select tests that are less or equal to the geometric mean of all the test times
    geomean1 | select tests that are less or equal to 2 × the geometric mean of all the test times
    geomean1 | select tests that are less or equal to 3 × the geometric mean of all the test times

--syscall-ops N
    stop after N system calls

--sysinfo N
    start N workers that continually read system and process specific information. This reads the process user and system times using the times(2) system call. For Linux systems, it also reads overall system statistics using the sysinfo(2) system call and also the file system statistics for all mounted file systems using statfs(2).

--sysinfo-ops N
    stop the sysinfo workers after N bogo operations.

--sysinval N
    start N workers that exercise system calls in random order with permutations of invalid arguments to force kernel error handling checks. The stress test autodetects system calls that cause processes to crash or exit prematurely and will blocklist these after several repeated breakages. System call arguments that cause system calls to work successfully are also detected an blocklisted too. Linux only.

--sysinval-ops N
    stop sysinval workers after N system call attempts.

--sysfs N
    start N workers that recursively read files from /sys (Linux only). This may cause specific kernel drivers to emit messages into the kernel log.

--sysfs-ops N
    stop sysfs reading after N bogo read operations. Note, since the number of entries may vary between kernels, this bogo ops metric is probably very misleading.

--tee N
    move data from a writer process to a reader process through pipes and to /dev/null without any copying between kernel address space and user address space using tee(2). This is only available for Linux.

--tee-ops N
    stop after N bogo tee operations.

-T N, --timer N
    start N workers creating timer events at a default rate of 1 MHz (Linux only); this can create a many thousands of timer clock interrupts. Each timer event is caught by a signal handler and counted as a bogo timer op.

--timer-freq F
    run timers at F Hz; range from 1 to 1000000000 Hz (Linux only). By selecting an appropriate frequency stress-ng can generate hundreds of thousands of interrupts per second. Note: it is also worth using --timer-slack 0 for high frequencies to stop the kernel from coalescing timer events.

--timer-ops N
    stop timer stress workers after N bogo timer events (Linux only).

--timer-rand
    select a timer frequency based around the timer frequency +/- 12.5% random jitter. This tries to force more variability in the timer interval to make the scheduling less predictable.

--timerfd N
    start N workers creating timerfd events at a default rate of 1 MHz (Linux only); this can create a many thousands of timer clock events. Timer events are waited for on the timer file descriptor using select(2) and then read and counted as a bogo timerfd op.

--timerfs-fds N
    try to use a maximum of N timerfd file descriptors per stressor.

--timerfd-freq F
    run timers at F Hz; range from 1 to 1000000000 Hz (Linux only). By selecting an appropriate frequency stress-ng can generate hundreds of thousands of interrupts per second.

--timerfd-ops N
    stop timerfd stress workers after N bogo timerfd events (Linux only).

--timerfd-rand
    select a timerfd frequency based around the timer frequency +/- 12.5% random jitter. This tries to force more variability in the timer interval to make the scheduling less predictable.

--tlb-shootdown N
    start N workers that force Translation Lookaside Buffer (TLB) shootdowns. This is achieved by creating up to 16 child processes that all share a region of memory and these processes are shared amongst the available CPUs. The processes adjust the page mapping settings causing TLBs to be force flushed on the other processors, causing the TLB shootdowns.

--tlb-shootdown-ops N
    stop after N bogo TLB shootdown operations are completed.

--tmpfs N
    start N workers that create a temporary file on an available tmpfs file system and perform various file based mmap operations upon it.

--tmpfs-mmap-async
    enable file based memory mapping and use asynchronous msync'ing on each page, see --tmpfs-mmap-file.

--tmpfs-mmap-file
    enable tmpfs file based memory mapping and by default use synchronous msync'ing on each page.

--tmpfs-ops N
    stop tmpfs stressors after N bogo mmap operations.

--touch N
    touch files by using open(2) or creat(2) and then closing and unlinking them. The filename contains the bogo-op number and is incremented on each touch operation, hence this fills the dentry cache. Note that the user time and system time may be very low as most of the run time is waiting for file I/O and this produces very large bogo-op rates for the very low CPU time used.

--touch-method [ random | open | creat ]
    select the method the file is created, either randomly using open(2) or create(2), just using open(2) with the O_CREAT open flag, or with creat(2).

--touch-ops N
    stop the touch workers after N file touches.

--touch-opts all, direct, dsync, excl, noatime, sync
    specify various file open options as a comma separated list. Options are as follows:
    Option | Description
    all | use all the open options, namely direct, dsync, excl, noatime and sync
    direct | try to minimize cache effects of the I/O to and from this file, using the O_DIRECT open flag.
    dsync | ensure output has been transferred to underlying hardware and file metadata has been updated using the O_DSYNC open flag.
    excl | fail if file already exists (it should not).
    noatime | do not update the file last access time if the file is read.
    sync | ensure output has been transferred to underlying hardware using the O_SYNC open flag.

--tree N
    start N workers that exercise tree data structures. The default is to add, find and remove 250,000 64 bit integers into AVL (avl), Red-Black (rb), Splay (splay), btree and binary trees. The intention of this stressor is to exercise memory and cache with the various tree operations.

--tree-method [ all | avl | binary | btree | rb | splay ]
    specify the tree to be used. By default, all the trees are used (the 'all' option).

--tree-ops N
    stop tree stressors after N bogo ops. A bogo op covers the addition, finding and removing all the items into the tree(s).

--tree-size N
    specify the size of the tree, where N is the number of 64 bit integers to be added into the tree.

--tsc N
    start N workers that read the Time Stamp Counter (TSC) 256 times per loop iteration (bogo operation). This exercises the tsc instruction for x86, the mftb instruction for ppc64, the rdcycle instruction for RISC-V and the tick instruction on SPARC.

--tsc-lfence
    add lfence after each tsc read to force serialization (x86 only).

--tsc-ops N
    stop the tsc workers after N bogo operations are completed.

--tsearch N
    start N workers that insert, search and delete 32 bit integers on a binary tree using tsearch(3), tfind(3) and tdelete(3). By default, there are 65536 randomized integers used in the tree. This is a useful method to exercise random access of memory and processor cache.

--tsearch-ops N
    stop the tsearch workers after N bogo tree operations are completed.

--tsearch-size N
    specify the size (number of 32 bit integers) in the array to tsearch. Size can be from 1K to 4M.

--tun N
    start N workers that create a network tunnel device and sends and receives packets over the tunnel using UDP and then destroys it. A new random 192.168.*.* IPv4 address is used each time a tunnel is created.

--tun-ops N
    stop after N iterations of creating/sending/receiving/destroying a tunnel.

--tun-tap
    use network tap device using level 2 frames (bridging) rather than a tun device for level 3 raw packets (tunnelling).

--udp N
    start N workers that transmit data using UDP. This involves a pair of client/server processes performing rapid connect, send and receives and disconnects on the local host.

--udp-domain D
    specify the domain to use, the default is ipv4. Currently ipv4, ipv6 and unix are supported.

--udp-gro
    enable UDP-GRO (Generic Receive Offload) if supported.

--udp-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--udp-lite
    use the UDP-Lite (RFC 3828) protocol (only for ipv4 and ipv6 domains).

--udp-ops N
    stop udp stress workers after N bogo operations.

--udp-port P
    start at port P. For N udp worker processes, ports P to P - 1 are used. By default, ports 7000 upwards are used.

--udp-flood N
    start N workers that attempt to flood the host with UDP packets to random ports. The IP address of the packets are currently not spoofed. This is only available on systems that support AF_PACKET.

--udp-flood-domain D
    specify the domain to use, the default is ipv4. Currently ipv4 and ipv6 are supported.

--udp-flood-if NAME
    use network interface NAME. If the interface NAME does not exist, is not up or does not support the domain then the loopback (lo) interface is used as the default.

--udp-flood-ops N
    stop udp-flood stress workers after N bogo operations.

--umount N
    start N workers that exercise mounting and racying unmounting of small tmpfs and ramfs file systems. Three child processes are invoked, one to mount, another to force umount and a third to exercice /proc/mounts. Small random delays are used between mount and umount calls to try to trigger race conditions on the umount calls.

--umount-ops N
    stop umount workers after N successful bogo mount/umount operations.

--unshare N
    start N workers that each fork off 32 child processes, each of which exercises the unshare(2) system call by disassociating parts of the process execution context. (Linux only).

--unshare-ops N
    stop after N bogo unshare operations.

--uprobe N
    start N workers that trace the entry to libc function getpid() using the Linux uprobe kernel tracing mechanism. This requires CAP_SYS_ADMIN capabilities and a modern Linux uprobe capable kernel.

--uprobe-ops N
    stop uprobe tracing after N trace events of the function that is being traced.

-u N, --urandom N
    start N workers reading /dev/urandom (Linux only). This will load the kernel random number source.

--urandom-ops N
    stop urandom stress workers after N urandom bogo read operations (Linux only).

--userfaultfd N
    start N workers that generate write page faults on a small anonymously mapped memory region and handle these faults using the user space fault handling via the userfaultfd mechanism. This will generate a large quantity of major page faults and also context switches during the handling of the page faults. (Linux only).

--userfaultfd-bytes N
    mmap N bytes per userfaultfd worker to page fault on, the default is 16MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--userfaultfd-ops N
    stop userfaultfd stress workers after N page faults.

--usersyscall N
    start N workers that exercise the Linux prctl userspace system call mechanism. A userspace system call is handled by a SIGSYS signal handler and exercised with the system call disabled (ENOSYS) and enabled (via SIGSYS) using prctl PR_SET_SYSCALL_USER_DISPATCH.

--usersyscall-ops N
    stop after N successful userspace syscalls via a SIGSYS signal handler.

--utime N
    start N workers updating file timestamps. This is mainly CPU bound when the default is used as the system flushes metadata changes only periodically.

--utime-fsync
    force metadata changes on each file timestamp update to be flushed to disk. This forces the test to become I/O bound and will result in many dirty metadata writes.

--utime-ops N
    stop utime stress workers after N utime bogo operations.

--vdso N
    start N workers that repeatedly call each of the system call functions in the vDSO (virtual dynamic shared object). The vDSO is a shared library that the kernel maps into the address space of all user-space applications to allow fast access to kernel data to some system calls without the need of performing an expensive system call.

--vdso-func F
    Instead of calling all the vDSO functions, just call the vDSO function F. The functions depend on the kernel being used, but are typically clock_gettime, getcpu, gettimeofday and time.

--vdso-ops N
    stop after N vDSO functions calls.

--vecfp N
    start N workers that exericise floating point (single and double precision) addition, multiplication, division and negation on vectors of 128, 64, 32, 16 and 8 floating point values. The -v option will show the approximate throughput in millions of floating pointer operations per second for each operation. For x86, the gcc/clang target clones attribute has been used to produced vector optimizations for a range of mmx, sse, avx and processor features.

--vecfp-method method
    specify a vecfp stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required.
    Method | Description
    all | iterate through all of the following vector methods
    floatv128add | addition of a vector of 128 single precision floating point values
    floatv64add | addition of a vector of 64 single precision floating point values
    floatv32add | addition of a vector of 32 single precision floating point values
    floatv16add | addition of a vector of 16 single precision floating point values
    floatv8add | addition of a vector of 8 single precision floating point values
    floatv128mul | multiplication of a vector of 128 single precision floating point values
    floatv64mul | multiplication of a vector of 64 single precision floating point values
    floatv32mul | multiplication of a vector of 32 single precision floating point values
    floatv16mul | multiplication of a vector of 16 single precision floating point values
    floatv8mul | multiplication of a vector of 8 single precision floating point values
    floatv128div | division of a vector of 128 single precision floating point values
    floatv64div | division of a vector of 64 single precision floating point values
    floatv32div | division of a vector of 32 single precision floating point values
    floatv16div | division of a vector of 16 single precision floating point values
    floatv8div | division of a vector of 8 single precision floating point values
    doublev128add | addition of a vector of 128 double precision floating point values
    doublev64add | addition of a vector of 64 double precision floating point values
    doublev32add | addition of a vector of 32 double precision floating point values
    doublev16add | addition of a vector of 16 double precision floating point values
    doublev8add | addition of a vector of 8 double precision floating point values
    doublev128mul | multiplication of a vector of 128 double precision floating point values
    doublev64mul | multiplication of a vector of 64 double precision floating point values
    doublev32mul | multiplication of a vector of 32 double precision floating point values
    doublev16mul | multiplication of a vector of 16 double precision floating point values
    doublev8mul | multiplication of a vector of 8 double precision floating point values
    doublev128div | division of a vector of 128 double precision floating point values
    doublev64div | division of a vector of 64 double precision floating point values
    doublev32div | division of a vector of 32 double precision floating point values
    doublev16div | division of a vector of 16 double precision floating point values
    doublev8div | division of a vector of 8 double precision floating point values
    doublev128neg | negation of a vector of 128 double precision floating point values
    doublev64neg | negation of a vector of 64 double precision floating point values
    doublev32neg | negation of a vector of 32 double precision floating point values
    doublev16neg | negation of a vector of 16 double precision floating point values
    doublev8neg | negation of a vector of 8 double precision floating point values

--vecfp-ops N
    stop after N vector floating point bogo-operations. Each bogo-op is equivalent to 65536 loops of 2 vector operations. For example, one bogo-op on a 16 wide vector is equivalent to 65536 × 2 × 16 floating point operations.

--vecmath N
    start N workers that perform various unsigned integer math operations on various 128 bit vectors. A mix of vector math operations are performed on the following vectors: 16 × 8 bits, 8 × 16 bits, 4 × 32 bits, 2 × 64 bits. The metrics produced by this mix depend on the processor architecture and the vector math optimisations produced by the compiler.

--vecmath-ops N
    stop after N bogo vector integer math operations.

--vecshuf N
    start N workers that shuffle data on various 64 byte vectors comprised of 8, 16, 32, 64 and 128 bit unsigned integers. The integers are shuffled around the vector with 4 shuffle operations per loop, 65536 loops make up one bogo-op of shuffling. The data shuffling rates and shuffle operation rates are logged when using the -v option. This stressor exercises vector load, shuffle/permute, packing/unpacking and store operations.

--vecshuf-method method
    specify a vector shuffling stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required.
    Method | Description
    all | iterate through all of the following vector methods
    u8x64 | shuffle a vector of 64 unsigned 8 bit integers
    u16x32 | shuffle a vector of 32 unsigned 16 bit integers
    u32x16 | shuffle a vector of 16 unsigned 32 bit integers
    u64x8 | shuffle a vector of 8 unsigned 64 bit integers
    u128x4 | shuffle a vector of 4 unsigned 128 bit integers (when supported)

--vecshuf-ops N
    stop after N bogo vector shuffle ops. One bogo-op is equavlent of 4 × 65536 vector shuffle operations on 64 bytes of vector data.

--vecwide N
    start N workers that perform various 8 bit math operations on vectors of 4, 8, 16, 32, 64, 128, 256, 512, 1024 and 2048 bytes. With the -v option the relative compute performance vs the expected compute performance based on total run time is shown for the first vecwide worker. The vecwide stressor exercises various processor vector instruction mixes and how well the compiler can map the vector operations to the target instruction set.

--vecwide-ops N
    stop after N bogo vector operations (2048 iterations of a mix of vector instruction operations).

--verity N
    start N workers that exercise read-only file based authenticy protection using the verity ioctls FS_IOC_ENABLE_VERITY and FS_IOC_MEASURE_VERITY. This requires file systems with verity support (currently ext4 and f2fs on Linux) with the verity feature enabled. The test attempts to creates a small file with multiple small extents and enables verity on the file and verifies it. It also checks to see if the file has verity enabled with the FS_VERITY_FL bit set on the file flags.

--verity-ops N
    stop the verity workers after N file create, enable verity, check verity and unlink cycles.

--vfork N
    start N workers continually vforking children that immediately exit.

--vfork-max P
    create P processes and then wait for them to exit per iteration. The default is just 1; higher values will create many temporary zombie processes that are waiting to be reaped. One can potentially fill up the process table using high values for --vfork-max and --vfork.

--vfork-ops N
    stop vfork stress workers after N bogo operations.

--vfork-vm
    deprecated since stress-ng V0.14.03

--vforkmany N
    start N workers that spawn off a chain of vfork children until the process table fills up and/or vfork fails. vfork can rapidly create child processes and the parent process has to wait until the child dies, so this stressor rapidly fills up the process table.

--vforkmany-ops N
    stop vforkmany stressors after N vforks have been made.

--vforkmany-vm
    enable detrimental performance virtual memory advice using madvise on all pages of the vforked process. Where possible this will try to set every page in the new process with using madvise MADV_MERGEABLE, MADV_WILLNEED, MADV_HUGEPAGE and MADV_RANDOM flags. Linux only.

-m N, --vm N
    start N workers continuously calling mmap(2)/munmap(2) and writing to the allocated memory. Note that this can cause systems to trip the kernel OOM killer on Linux systems if not enough physical memory and swap is not available.

--vm-bytes N
    mmap N bytes per vm worker, the default is 256MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--vm-hang N
    sleep N seconds before unmapping memory, the default is zero seconds. Specifying 0 will do an infinite wait.

--vm-keep
    do not continually unmap and map memory, just keep on re-writing to it.

--vm-locked
    Lock the pages of the mapped region into memory using mmap MAP_LOCKED (since Linux 2.5.37). This is similar to locking memory as described in mlock(2).

--vm-madvise advice
    Specify the madvise 'advice' option used on the memory mapped regions used in the vm stressor. Non-linux systems will only have the 'normal' madvise advice, linux systems support 'dontneed', 'hugepage', 'mergeable' , 'nohugepage', 'normal', 'random', 'sequential', 'unmergeable' and 'willneed' advice. If this option is not used then the default is to pick random madvise advice for each mmap call. See madvise(2) for more details.

--vm-method method
    specify a vm stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required. Each of the vm workers have 3 phases:

    1. Initialised. The anonymously memory mapped region is set to a known pattern.

    2. Exercised. Memory is modified in a known predictable way. Some vm workers alter memory sequentially, some use small or large strides to step along memory.

    3. Checked. The modified memory is checked to see if it matches the expected result.

    The vm methods containing 'prime' in their name have a stride of the largest prime less than 2↑64, allowing to them to thoroughly step through memory and touch all locations just once while also doing without touching memory cells next to each other. This strategy exercises the cache and page non-locality.

    Since the memory being exercised is virtually mapped then there is no guarantee of touching page addresses in any particular physical order. These workers should not be used to test that all the system's memory is working correctly either, use tools such as memtest86 instead.

    The vm stress methods are intended to exercise memory in ways to possibly find memory issues and to try to force thermal errors.

    Available vm stress methods are described as follows:
    Method | Description
    all | iterate over all the vm stress methods as listed below.
    cache-lines | work through memory in 64 byte cache sized steps writing a single byte per cache line. Once the write is complete, the memory is read to verify the values are written correctly.
    cache-stripe | work through memory in 64 byte cache sized chunks, writing in ascending address order on even offsets and descending address order on odd offsets.
    checkboard | work through memory writing alternative zero/one bit values into memory in a mixed checkerboard pattern. Memory is swapped around to ensure every bit is read, bit flipped and re-written and then re-read for verification.
    flip | sequentially work through memory 8 times, each time just one bit in memory flipped (inverted). This will effectively invert each byte in 8 passes.
    fwdrev | write to even addressed bytes in a forward direction and odd addressed bytes in reverse direction. rhe contents are sanity checked once all the addresses have been written to.
    galpat-0 | galloping pattern zeros. This sets all bits to 0 and flips just 1 in 4096 bits to 1. It then checks to see if the 1s are pulled down to 0 by their neighbours or of the neighbours have been pulled up to 1.
    galpat-1 | galloping pattern ones. This sets all bits to 1 and flips just 1 in 4096 bits to 0. It then checks to see if the 0s are pulled up to 1 by their neighbours or of the neighbours have been pulled down to 0.
    gray | fill the memory with sequential gray codes (these only change 1 bit at a time between adjacent bytes) and then check if they are set correctly.
    grayflip | fill memory with adjacent bytes of gray code and inverted gray code pairs to change as many bits at a time between adjacent bytes and check if these are set correctly.
    incdec | work sequentially through memory twice, the first pass increments each byte by a specific value and the second pass decrements each byte back to the original start value. The increment/decrement value changes on each invocation of the stressor.
    inc-nybble | initialise memory to a set value (that changes on each invocation of the stressor) and then sequentially work through each byte incrementing the bottom 4 bits by 1 and the top 4 bits by 15.
    lfsr32 | fill memory with values generated from a 32 bit Galois linear feedback shift register using the polynomial x↑32 + x↑31 + x↑29 + x + 1. This generates a ring of 2↑32 - 1 unique values (all 32 bit values except for 0).
    rand-set | sequentially work through memory in 64 bit chunks setting bytes in the chunk to the same 8 bit random value. The random value changes on each chunk. Check that the values have not changed.
    rand-sum | sequentially set all memory to random values and then summate the number of bits that have changed from the original set values.
    read64 | sequentially read memory using 32 × 64 bit reads per bogo loop. Each loop equates to one bogo operation. This exercises raw memory reads.
    ror | fill memory with a random pattern and then sequentially rotate 64 bits of memory right by one bit, then check the final load/rotate/stored values.
    swap | fill memory in 64 byte chunks with random patterns. Then swap each 64 chunk with a randomly chosen chunk. Finally, reverse the swap to put the chunks back to their original place and check if the data is correct. This exercises adjacent and random memory load/stores.
    move-inv | sequentially fill memory 64 bits of memory at a time with random values, and then check if the memory is set correctly. Next, sequentially invert each 64 bit pattern and again check if the memory is set as expected.
    modulo-x | fill memory over 23 iterations. Each iteration starts one byte further along from the start of the memory and steps along in 23 byte strides. In each stride, the first byte is set to a random pattern and all other bytes are set to the inverse. Then it checks see if the first byte contains the expected random pattern. This exercises cache store/reads as well as seeing if neighbouring cells influence each other.
    mscan | fill each bit in each byte with 1s then check these are set, fill each bit in each byte with 0s and check these are clear.
    prime-0 | iterate 8 times by stepping through memory in very large prime strides clearing just on bit at a time in every byte. Then check to see if all bits are set to zero.
    prime-1 | iterate 8 times by stepping through memory in very large prime strides setting just on bit at a time in every byte. Then check to see if all bits are set to one.
    prime-gray-0 | first step through memory in very large prime strides clearing just on bit (based on a gray code) in every byte. Next, repeat this but clear the other 7 bits. Then check to see if all bits are set to zero.
    prime-gray-1 | first step through memory in very large prime strides setting just on bit (based on a gray code) in every byte. Next, repeat this but set the other 7 bits. Then check to see if all bits are set to one.
    rowhammer | try to force memory corruption using the rowhammer memory stressor. This fetches two 32 bit integers from memory and forces a cache flush on the two addresses multiple times. This has been known to force bit flipping on some hardware, especially with lower frequency memory refresh cycles.
    walk-0d | for each byte in memory, walk through each data line setting them to low (and the others are set high) and check that the written value is as expected. This checks if any data lines are stuck.
    walk-1d | for each byte in memory, walk through each data line setting them to high (and the others are set low) and check that the written value is as expected. This checks if any data lines are stuck.
    walk-0a | in the given memory mapping, work through a range of specially chosen addresses working through address lines to see if any address lines are stuck low. This works best with physical memory addressing, however, exercising these virtual addresses has some value too.
    walk-1a | in the given memory mapping, work through a range of specially chosen addresses working through address lines to see if any address lines are stuck high. This works best with physical memory addressing, however, exercising these virtual addresses has some value too.
    write64 | sequentially write to memory using 32 × 64 bit writes per bogo loop. Each loop equates to one bogo operation. This exercises raw memory writes. Note that memory writes are not checked at the end of each test iteration.
    write64nt | sequentially write to memory using 32 × 64 bit non-temporal writes per bogo loop. Each loop equates to one bogo operation. This exercises cacheless raw memory writes and is only available on x86 sse2 capable systems built with gcc and clang compilers. Note that memory writes are not checked at the end of each test iteration.
    write1024v | sequentially write to memory using 1 × 1024 bit vector write per bogo loop (only available if the compiler supports vector types). Each loop equates to one bogo operation. This exercises raw memory writes. Note that memory writes are not checked at the end of each test iteration.
    wrrd128nt | write to memory in 128 bit chunks using non-temporal writes (bypassing the cache). Each chunk is written 4 times to hammer the memory. Then check to see if the data is correct using non-temporal reads if they are available or normal memory reads if not. Only available with processors that provide non-temporal 128 bit writes.
    zero-one | set all memory bits to zero and then check if any bits are not zero. Next, set all the memory bits to one and check if any bits are not one.

--vm-ops N
    stop vm workers after N bogo operations.

--vm-populate
    populate (prefault) page tables for the memory mappings; this can stress swapping. Only available on systems that support MAP_POPULATE (since Linux 2.5.46).

--vm-addr N
    start N workers that exercise virtual memory addressing using various methods to walk through a memory mapped address range. This will exercise mapped private addresses from 8MB to 64MB per worker and try to generate cache and TLB inefficient addressing patterns. Each method will set the memory to a random pattern in a write phase and then sanity check this in a read phase.

--vm-addr-method method
    specify a vm address stress method. By default, all the stress methods are exercised sequentially, however one can specify just one method to be used if required.

    Available vm address stress methods are described as follows:
    Method | Description
    all | iterate over all the vm stress methods as listed below.
    bitposn | iteratively write to memory in powers of 2 strides of max_stride to 1 and then read check memory in powers of 2 strides 1 to max_stride where max_stride is half the size of the memory mapped region. All bit positions of the memory address space are bit flipped in the striding.
    dec | work through the address range backwards sequentially, byte by byte.
    decinv | like dec, but with all the relevant address bits inverted.
    flip | address memory using gray coded addresses and their inverse to flip as many address bits per write/read operation
    gray | work through memory with gray coded addresses so that each change of address just changes 1 bit compared to the previous address.
    grayinv | like gray, but with the all relevant address bits inverted, hence all bits change apart from 1 in the address range.
    inc | work through the address range forwards sequentially, byte by byte.
    incinv | like inc, but with all the relevant address bits inverted.
    pwr2 | work through memory addresses in steps of powers of two.
    pwr2inv | like pwr2, but with the all relevant address bits inverted.
    rev | work through the address range with the bits in the address range reversed.
    revinv | like rev, but with all the relevant address bits inverted.

--vm-addr-mlock
    attempt to mlock pages into memory causing more memory pressure by preventing pages from swapped out.

--vm-addr-ops N
    stop N workers after N bogo addressing passes.

--vm-rw N
    start N workers that transfer memory to/from a parent/child using process_vm_writev(2) and process_vm_readv(2). This is feature is only supported on Linux. Memory transfers are only verified if the --verify option is enabled.

--vm-rw-bytes N
    mmap N bytes per vm-rw worker, the default is 16MB. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--vm-rw-ops N
    stop vm-rw workers after N memory read/writes.

--vm-segv N
    start N workers that create a child process that unmaps its address space causing a SIGSEGV on return from the unmap.

--vm-segv-ops N
    stop after N bogo vm-segv SIGSEGV faults.

--vm-splice N
    move data from memory to /dev/null through a pipe without any copying between kernel address space and user address space using vmsplice(2) and splice(2). This is only available for Linux.

--vm-splice-bytes N
    transfer N bytes per vmsplice call, the default is 64K. One can specify the size as % of total available memory or in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g.

--vm-splice-ops N
    stop after N bogo vm-splice operations.

--wait N
    start N workers that spawn off two children; one spins in a pause(2) loop, the other continually stops and continues the first. The controlling process waits on the first child to be resumed by the delivery of SIGCONT using waitpid(2) and waitid(2).

--wait-ops N
    stop after N bogo wait operations.

--waitcpu N
    start N workers that exercise processor wait instructions. For x86 these are pause, tpause and umwait (when available) and nop. For ARM the yield instruction is used. For other architectures currently nop instructions are used.

--waitcpu-ops N
    stop after N bogo processor wait operations.

--watchdog N
    start N workers that exercising the /dev/watchdog watchdog interface by opening it, perform various watchdog specific ioctl(2) commands on the device and close it. Before closing the special watchdog magic close message is written to the device to try and force it to never trip a watchdog reboot after the stressor has been run. Note that this stressor needs to be run as root with the --pathological option and is only available on Linux.

--watchdog-ops N
    stop after N bogo operations on the watchdog device.

--wcs N
    start N workers that exercise various libc wide character string functions on random strings.

--wcs-method wcsfunc
    select a specific libc wide character string function to stress. Available string functions to stress are: all, wcscasecmp, wcscat, wcschr, wcscoll, wcscmp, wcscpy, wcslen, wcsncasecmp, wcsncat, wcsncmp, wcsrchr and wcsxfrm. The 'all' method is the default and will exercise all the string methods.

--wcs-ops N
    stop after N bogo wide character string operations.

--x86cpuid N
    start N workers that exercise the x86 cpuid instruction with 18 different leaf types.

--x86cpuid-ops N
    stop after N iterations that exercise the different cpuid leaf types.

--x86syscall N
    start N workers that repeatedly exercise the x86-64 syscall instruction to call the getpid(2), getcpu(2), gettimeofday(2) and time(2) system using the Linux vsyscall handler. Only for Linux.

--x86syscall-func F
    Instead of exercising the 4 syscall system calls, just call the syscall function F. The function F must be one of getcpu, gettimeofday and time.

--x86syscall-ops N
    stop after N x86syscall system calls.

--xattr N
    start N workers that create, update and delete batches of extended attributes on a file.

--xattr-ops N
    stop after N bogo extended attribute operations.

-y N, --yield N
    start N workers that call sched_yield(2). This stressor ensures that at least 2 child processes per CPU exercise shield_yield(2) no matter how many workers are specified, thus always ensuring rapid context switching.

--yield-ops N
    stop yield stress workers after N sched_yield(2) bogo operations.

--zero N
    start N workers reading /dev/zero.

--zero-ops N
    stop zero stress workers after N /dev/zero bogo read operations.

--zlib N
    start N workers compressing and decompressing random data using zlib. Each worker has two processes, one that compresses random data and pipes it to another process that decompresses the data. This stressor exercises CPU, cache and memory.

--zlib-level L
    specify the compression level (0..9), where 0 = no compression, 1 = fastest compression and 9 = best compression.

--zlib-mem-level L
    specify the reserved compression state memory for zlib. Default is 8.
    Value
    1 | minimum memory usage.
    9 | maximum memory usage.

--zlib-method method
    specify the type of random data to send to the zlib library. By default, the data stream is created from a random selection of the different data generation processes. However one can specify just one method to be used if required. Available zlib data generation methods are described as follows:
    Method | Description
    00ff | randomly distributed 0x00 and 0xFF values.
    ascii01 | randomly distributed ASCII 0 and 1 characters.
    asciidigits | randomly distributed ASCII digits in the range of 0 and 9.
    bcd | packed binary coded decimals, 0..99 packed into 2 4-bit nybbles.
    binary | 32 bit random numbers.
    brown | 8 bit brown noise (Brownian motion/Random Walk noise).
    double | double precision floating point numbers from sin(θ).
    fixed | data stream is repeated 0x04030201.
    gcr | random values as 4 × 4 bit data turned into 4 × 5 bit group coded recording (GCR) patterns. Each 5 bit GCR value starts or ends with at most one zero bit so that concatenated GCR codes have no more than two zero bits in a row.
    gray | 16 bit gray codes generated from an incrementing counter.
    inc16 | 16 bit incrementing values starting from a random 16 bit value.
    latin | Random latin sentences from a sample of Lorem Ipsum text.
    lehmer | Fast random values generated using Lehmer's generator using a 128 bit multiply.
    lfsr32 | Values generated from a 32 bit Galois linear feedback shift register using the polynomial x↑32 + x↑31 + x↑29 + x + 1. This generates a ring of 2↑32 - 1 unique values (all 32 bit values except for 0).
    logmap | Values generated from a logistical map of the equation Χn+1 = r × Χn × (1 - Χn) where r > ≈ 3.56994567 to produce chaotic data. The values are scaled by a large arbitrary value and the lower 8 bits of this value are compressed.
    lrand48 | Uniformly distributed pseudo-random 32 bit values generated from lrand48(3).
    morse | Morse code generated from random latin sentences from a sample of Lorem Ipsum text.
    nybble | randomly distributed bytes in the range of 0x00 to 0x0f.
    objcode | object code selected from a random start point in the stress-ng text segment.
    parity | 7 bit binary data with 1 parity bit.
    pink | pink noise in the range 0..255 generated using the Gardner method with the McCartney selection tree optimization. Pink noise is where the power spectral density is inversely proportional to the frequency of the signal and hence is slightly compressible.
    random | segments of the data stream are created by randomly calling the different data generation methods.
    rarely1 | data that has a single 1 in every 32 bits, randomly located.
    rarely0 | data that has a single 0 in every 32 bits, randomly located.
    rdrand | x86-64 only, generate random data using rdrand instruction.
    ror32 | generate a 32 bit random value, rotate it right 0 to 7 places and store the rotated value for each of the rotations.
    text | random ASCII text.
    utf8 | random 8 bit data encoded to UTF-8.
    zero | all zeros, compresses very easily.

--zlib-ops N
    stop after N bogo compression operations, each bogo compression operation is a compression of 64K of random data at the highest compression level.

--zlib-strategy S
    specifies the strategy to use when deflating data. This is used to tune the compression algorithm. Default is 0.
    Value
    0 | used for normal data (Z_DEFAULT_STRATEGY).
    1 | for data generated by a filter or predictor (Z_FILTERED)
    2 | forces huffman encoding (Z_HUFFMAN_ONLY).
    3 | Limit match distances to one run-length-encoding (Z_RLE).
    4 | prevents dynamic huffman codes (Z_FIXED).

--zlib-stream-bytes S
    specify the amount of bytes to deflate until deflate should finish the block and return with Z_STREAM_END. One can specify the size in units of Bytes, KBytes, MBytes and GBytes using the suffix b, k, m or g. Default is 0 which creates and endless stream until stressor ends.
    Value
    0 | creates an endless deflate stream until stressor stops.
    n | creates an stream of n bytes over and over again.
     | Each block will be closed with Z_STREAM_END.

--zlib-window-bits W
    specify the window bits used to specify the history buffer size. The value is specified as the base two logarithm of the buffer size (e.g. value 9 is 2↑9 = 512 bytes). Default is 15.
    Value
    -8-(-15) | raw deflate format.
    8-15 | zlib format.
    24-31 | gzip format.
    40-47 | inflate auto format detection using zlib deflate format.

--zombie N
    start N workers that create zombie processes. This will rapidly try to create a default of 8192 child processes that immediately die and wait in a zombie state until they are reaped. Once the maximum number of processes is reached (or fork fails because one has reached the maximum allowed number of children) the oldest child is reaped and a new process is then created in a first-in first-out manner, and then repeated.

--zombie-max N
    try to create as many as N zombie processes. This may not be reached if the system limit is less than N.

--zombie-ops N
    stop zombie stress workers after N bogo zombie operations.

EXAMPLES

stress-ng --vm 8 --vm-bytes 80% -t 1h

    run 8 virtual memory stressors that combined use 80% of the available memory for 1 hour. Thus each stressor uses 10% of the available memory.

stress-ng --cpu 4 --io 2 --vm 1 --vm-bytes 1G --timeout 60s

    runs for 60 seconds with 4 cpu stressors, 2 io stressors and 1 vm stressor using 1GB of virtual memory.

stress-ng --iomix 2 --iomix-bytes 10% -t 10m

    runs 2 instances of the mixed I/O stressors using a total of 10% of the available file system space for 10 minutes. Each stressor will use 5% of the available file system space.

stress-ng --cyclic 1 --cyclic-dist 2500 --cyclic-method clock_ns --cyclic-prio 100 --cyclic-sleep 10000 --hdd 0 -t 1m

    measures real time scheduling latencies created by the hdd stressor. This uses the high resolution nanosecond clock to measure latencies during sleeps of 10,000 nanoseconds. At the end of 1 minute of stressing, the latency distribution with 2500 ns intervals will be displayed. NOTE: this must be run with the CAP_SYS_NICE capability to enable the real time scheduling to get accurate measurements.

stress-ng --cpu 8 --cpu-ops 800000

    runs 8 cpu stressors and stops after 800000 bogo operations.

stress-ng --sequential 2 --timeout 2m --metrics

    run 2 simultaneous instances of all the stressors sequentially one by one, each for 2 minutes and summarise with performance metrics at the end.

stress-ng --cpu 4 --cpu-method fft --cpu-ops 10000 --metrics-brief

    run 4 FFT cpu stressors, stop after 10000 bogo operations and produce a summary just for the FFT results.

stress-ng --cpu -1 --cpu-method all -t 1h --cpu-load 90

    run cpu stressors on all online CPUs working through all the available CPU stressors for 1 hour, loading the CPUs at 90% load capacity.

stress-ng --cpu 0 --cpu-method all -t 20m

    run cpu stressors on all configured CPUs working through all the available CPU stressors for 20 minutes

stress-ng --all 4 --timeout 5m

    run 4 instances of all the stressors for 5 minutes.

stress-ng --random 64

    run 64 stressors that are randomly chosen from all the available stressors.

stress-ng --cpu 64 --cpu-method all --verify -t 10m --metrics-brief

    run 64 instances of all the different cpu stressors and verify that the computations are correct for 10 minutes with a bogo operations summary at the end.

stress-ng --sequential -1 -t 10m

    run all the stressors one by one for 10 minutes, with the number of instances of each stressor matching the number of online CPUs.

stress-ng --sequential 8 --class io -t 5m --times

    run all the stressors in the io class one by one for 5 minutes each, with 8 instances of each stressor running concurrently and show overall time utilisation statistics at the end of the run.

stress-ng --all -1 --maximize --aggressive

    run all the stressors (1 instance of each per online CPU) simultaneously, maximize the settings (memory sizes, file allocations, etc.) and select the most demanding/aggressive options.

stress-ng --random 32 -x numa,hdd,key

    run 32 randomly selected stressors and exclude the numa, hdd and key stressors

stress-ng --sequential 4 --class vm --exclude bigheap,brk,stack

    run 4 instances of the VM stressors one after each other, excluding the bigheap, brk and stack stressors

stress-ng --taskset 0,2-3 --cpu 3

    run 3 instances of the CPU stressor and pin them to CPUs 0, 2 and 3.

EXIT STATUS
Status | Description
0 | Success.
1 | Error; incorrect user options or a fatal resource issue in the stress-ng stressor harness (for example, out of memory).
2 | One or more stressors failed.
3 | One or more stressors failed to initialise because of lack of resources, for example ENOMEM (no memory), ENOSPC (no space on file system) or a missing or unimplemented system call.
4 | One or more stressors were not implemented on a specific architecture or operating system.
5 | A stressor has been killed by an unexpected signal.
6 | A stressor exited by exit(2) which was not expected and timing metrics could not be gathered.
7 | The bogo ops metrics maybe untrustworthy. This is most likely to occur when a stress test is terminated during the update of a bogo-ops counter such as when it has been OOM killed. A less likely reason is that the counter ready indicator has been corrupted.

BUGS
File bug reports at: https://github.com/ColinIanKing/stress-ng/issues

SEE ALSO
cpuburn(1), perf(1), stress(1), taskset(1)
https://github.com/ColinIanKing/stress-ng/blob/master/README.md

AUTHOR
stress-ng was written by Colin Ian King <colin.i.king@gmail.com> and is a clean room re-implementation and extension of the original stress tool by Amos Waterland. Thanks also to the many contributors to stress-ng. The README.md file in the source contains a full list of the contributors.

NOTES
Sending a SIGALRM, SIGINT or SIGHUP to stress-ng causes it to terminate all the stressor processes and ensures temporary files and shared memory segments are removed cleanly.

Sending a SIGUSR2 to stress-ng will dump out the current load average and memory statistics.

Note that the stress-ng cpu, io, vm and hdd tests are different implementations of the original stress tests and hence may produce different stress characteristics.

The bogo operations metrics may change with each release because of bug fixes to the code, new features, compiler optimisations or changes in system call performance.

COPYRIGHT
Copyright © 2013-2021 Canonical Ltd, Copyright © 2021-2023 Colin Ian King.
This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.