# 10.9. Launching with PBS / Torque

Open MPI supports PBS, PBS Pro, Torque, and other related resource managers.

## 10.9.1. Verify PBS/Torque support

The `prte_info` command can be used to determine whether or not an installed Open MPI includes Torque/PBS Pro support:

    shell$ prte_info | grep ras

If the Open MPI installation includes support for PBS/Torque, you should see a line similar to that below. Note the MCA version information varies depending on which version of Open MPI is installed.

    MCA ras: tm (MCA v2.1.0, API v2.0.0, Component v3.0.0)

Note

PRRTE is the software layer that provides run-time environment support to Open MPI. Open MPI typically hides most PMIx and PRRTE details from the end user, but this is one place that Open MPI is unable to hide the fact that PRRTE provides this functionality, not Open MPI. Hence, users need to use the `prte_info` command to check for PBS/Torque support (not `ompi_info`).

## 10.9.2. Launching

When properly configured, Open MPI obtains both the list of hosts and how many processes to start on each host from Torque / PBS Pro directly. Hence, it is unnecessary to specify the `--hostfile`, `--host`, or `-n` options to `mpirun`. Open MPI will use PBS/Torque-native mechanisms to launch and kill processes (`ssh` is not required).

For example:

    # Allocate a PBS job with 4 nodes
    shell$ qsub -I -lnodes=4

    # Now run an Open MPI job on all the nodes allocated by PBS/Torque
    shell$ mpirun mpi-hello-world

This will run the MPI processes on the nodes that were allocated by PBS/Torque. Or, if submitting a script:

    shell$ cat my_script.sh
    #!/bin/sh
    mpirun mpi-hello-world
    shell$ qsub -l nodes=4 my_script.sh

Warning

Do not modify `$PBS_NODEFILE`!

We’ve had reports from some sites that system administrators modify the `$PBS_NODEFILE` in each job according to local policies. This will currently cause Open MPI to behave in an unpredictable fashion. As long as no new hosts are added to the hostfile, it usually means that Open MPI will incorrectly map processes to hosts, but in some cases it can cause Open MPI to fail to launch processes altogether.