# 5.10. Installation location

A common environment to run PMIx is in a “Beowulf”-class or similar cluster (e.g., a bunch of 1U servers in a bunch of racks). Simply stated, PMIx can run on a group of servers or workstations connected by a network.

This raises the question for PMIx system administrators: where to install the PMIx binaries, header files, etc.? This discussion mainly addresses this question for homogeneous clusters (i.e., where all nodes and operating systems are the same), although elements of this discussion apply to heterogeneous clusters as well.

Important

For simplicity, the PMIx team strongly recommends that you install PMIx at the same path location on all nodes in your cluster. This greatly simplifies the user experience of running jobs across multiple nodes in your cluster.

It is possible to install PMIx in unique path locations in the different nodes in your cluster, but it is not advisable.

## 5.10.1. Filesystem types

There are two common approaches.

### 5.10.1.1. Network filesystem

Have a common filesystem, such as NFS, between all the machines to be used. Install PMIx such that the installation directory is the same value on each node. This will greatly simplify user’s shell startup scripts (e.g., `.bashrc`, `.cshrc`, `.profile` etc.) — the `PATH` can be set without checking which machine the user is on. It also simplifies the system administrator’s job; when the time comes to patch or otherwise upgrade PMIx, only one copy needs to be modified.

For example, consider a cluster of four machines: `inky`, `blinky`, `pinky`, and `clyde`.

- Install PMIx on `inky`’s local hard drive in the directory `/opt/pmix-VERSION`. The system administrator then mounts `inky:/opt/pmix-VERSION` on the remaining three machines, such that `/opt/pmix-VERSION` on all machines is effectively “the same”. That is, the following directories all contain the PMIx installation:

      inky:/opt/pmix-VERSION
      blinky:/opt/pmix-VERSION
      pinky:/opt/pmix-VERSION
      clyde:/opt/pmix-VERSION

- Install PMIx on `inky`’s local hard drive in the directory `/usr/local/pmix-VERSION`. The system administrator then mounts `inky:/usr/local/pmix-VERSION` on all four machines in some other common location, such as `/opt/pmix-VERSION` (a symbolic link can be installed on `inky` instead of a mount point for efficiency). This strategy is typically used for environments where one tree is NFS exported, but another tree is typically used for the location of actual installation. For example, the following directories all contain the PMIx installation:

      inky:/opt/pmix-VERSION
      blinky:/opt/pmix-VERSION
      pinky:/opt/pmix-VERSION
      clyde:/opt/pmix-VERSION

  Notice that there are the same four directories as the previous example, but on `inky`, the directory is actually located in `/usr/local/pmix-VERSION`.

There is a bit of a disadvantage in this approach; each of the remote nodes have to incur NFS (or whatever filesystem is used) delays to access the PMIx directory tree. However, both the administration ease and low cost (relatively speaking) of using a networked file system usually greatly outweighs the cost.

### 5.10.1.2. Local filesystem

If you are concerned with networked filesystem costs of accessing the PMIx binaries, you can install PMIx on the local hard drive of each node in your system. Again, it is highly advisable to install PMIx in the same directory on each node so that each user’s `PATH` can be set to the same value, regardless of the node that a user has logged on to.

This approach will save some network latency of accessing the PMIx binaries, but is typically only used where users are very concerned about squeezing every single cycle out of their machines, or are running at extreme scale where a networked filesystem may get overwhelmed by filesystem requests for PMIx binaries when running very large parallel jobs.

## 5.10.2. Installing over a prior PMIx installation

Warning

The PMIx team does not recommend installing a new version of PMIx over an existing / older installation of PMIx.

In its default configuration, an PMIx installation consists of several shared libraries, header files, executables, and plugins (dynamic shared objects — DSOs). These installation files act together as a single entity. The specific filenames and contents of these files are subject to change between different versions of PMIx.

Important

Installing one version of PMIx does not uninstall another version.

If you install a new version of PMIx over an older version, this may not overwrite all the files from the older version. Hence, you may end up with an incompatible muddle of files from two different installations — which can cause problems.

The PMIx team recommends one of the following methods for upgrading your PMIx installation:

- Install newer versions of PMIx into a different directory. For example, install into `/opt/pmix-a.b.c` and `/opt/pmix-x.y.z` for versions a.b.c and x.y.z, respectively.

- Completely uninstall the old version of PMIx before installing the new version. The `make uninstall` process from PMIx a.b.c build tree should completely uninstall that version from the installation tree, making it safe to install a new version (e.g., version x.y.z) into the same installation tree.

- Remove the old installation directory entirely and then install the new version. For example `rm -rf /opt/pmix` (assuming that there is nothing else of value in this tree!) The installation of PMIx x.y.z will safely re-create the `/opt/pmix` tree. This method is preferable if you no longer have the source and build trees to PMIx a.b.c available from which to `make uninstall`.

- Go into the PMIx a.b.c installation directory and manually remove all old PMIx files. Then install PMIx x.y.z into the same installation directory. This can be a somewhat painful, annoying, and error-prone process. We do not recommend it. Indeed, if you no longer have access to the original PMIx a.b.c source and build trees, it may be far simpler to download PMIx version a.b.c again from the PMIx web site, configure it with the same installation prefix, and then run `make uninstall`. Or use one of the other methods, above.

## 5.10.3. Relocating an PMIx installation

It can be desirable to initially install PMIx to one location (e.g., `/path/to/pmix`) and then later move it to another location (e.g., `/opt/myproduct/bundled-pmix-a.b.c`).

Note

PMIx hard-codes some directory paths in its executables based on installation paths specified by the `configure` script. For example, if you configure with an installation prefix of `/opt/pmix/`, PMIx encodes in its executables that it should be able to find its help files in `/opt/pmix/share/pmix`.

The “installdirs” functionality in PMIx lets you change any of these hard-coded directory paths at run time (assuming that you have already adjusted your `PATH` and/or `LD_LIBRARY_PATH` environment variables to the new location where PMIx now resides).

There are three methods.

### 5.10.3.1. Move an existing PMIx installation to a new prefix

Set the `PMIX_PREFIX` environment variable before launching a PMIx-based application. For example, if PMIx had initially been installed to `/opt/pmix` and the entire `pmix` tree was later moved to `/home/pmix`, setting `PMIX_PREFIX` to `/home/pmix` will enable PMIx to function properly.

### 5.10.3.2. “Stage” an PMIx installation in a temporary location

When creating self-contained installation packages, systems such as RPM install PMIx into temporary locations. The package system then bundles up everything under the temporary location into a package that can be installed into its real location later. For example, when creating an RPM that will be installed to `/opt/pmix`, the RPM system will transparently prepend a “destination directory” (or “destdir”) to the installation directory. As such, PMIx will think that it is installed in `/opt/pmix`, but it is actually temporarily installed in (for example) `/var/rpm/build.1234/opt/pmix`. If it is necessary to use PMIx while it is installed in this staging area, the `PMIX_DESTDIR` environment variable can be used; setting `PMIX_DESTDIR` to `/var/rpm/build.1234` will automatically prefix every directory such that PMIx can function properly.

### 5.10.3.3. Overriding individual directories

PMIx uses the GNU-specified directories (per Autoconf/Automake), and can be overridden by setting environment variables directly related to their common names. The list of environment variables that can be used is:

- `PMIX_PREFIX`

- `PMIX_EXEC_PREFIX`

- `PMIX_BINDIR`

- `PMIX_SBINDIR`

- `PMIX_LIBEXECDIR`

- `PMIX_DATAROOTDIR`

- `PMIX_DATADIR`

- `PMIX_SYSCONFDIR`

- `PMIX_SHAREDSTATEDIR`

- `PMIX_LOCALSTATEDIR`

- `PMIX_LIBDIR`

- `PMIX_INCLUDEDIR`

- `PMIX_INFODIR`

- `PMIX_MANDIR`

- `PMIX_PKGDATADIR`

- `PMIX_PKGLIBDIR`

- `PMIX_PKGINCLUDEDIR`

Note that not all of the directories listed above are used by PMIx; they are listed here in entirety for completeness.

Also note that several directories listed above are defined in terms of other directories. For example, the `$bindir` is defined by default as `$prefix/bin`. Hence, overriding the `$prefix` (via `PMIX_PREFIX`) will automatically change the first part of the `$bindir` (which is how method 1 described above works). Alternatively, `PMIX_BINDIR` can be set to an absolute value that ignores `$prefix` altogether.