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Interactive Slurm jobs

Interactive jobs allow a user to interact with applications on the compute nodes. With an interactive job, you request time and resources to work on a compute node directly, which is different to a batch job where you submit your job to a queue for later execution.

You can use two commands to create an interactive session: srun and salloc. Both of these commands take options similar to sbatch.

Using salloc

Using salloc, you allocate resources and spawn a shell that is then used to execute parallel tasks launched with srun. For example, you can allocate 2 nodes for 30 minutes with the command

$ salloc --nodes=2 --account=<project> --time=00:30:00
salloc: Granted job allocation 123456
salloc: Waiting for resource configuration

Once the allocation is made, this command will start a shell on the login node. You can start parallel execution on the allocated nodes with srun.

$ srun --ntasks=32 --cpus-per-task=8 ./mpi_openmp_application

After the execution of your application ended, the allocation can be terminated by exiting the shell (exit).

When using salloc, a shell is spawned on the login node. If you want to obtain a shell on the first allocated compute node you can use srun --pty.

$ srun --cpu_bind=none --nodes=2 --pty bash -i

If you want to use an application with a GUI, you can use the --x11 flag with srun to enable X11 forwarding.

Using srun

For simple interactive session, you can use srun with no prior allocation. In this scenario, srun will first create a resource allocation in which to run the job. For example, to allocate 1 node for 30 minutes and spawn a shell

$ srun --account=<project> --time=00:30:00 --nodes=1 --pty bash

Using srun to check running jobs

Currently, ssh'ing to compute nodes is not allowed, but the srun command can be used to check in on a running job in the cluster. In this case, you need to give the job ID and possibly also the specific name of a compute node to srun.

This starts a shell, where you can run any command, on the first allocated node in a specific job:

$ srun --interactive --pty --jobid=<jobid> $SHELL

To check processor and memory usage quickly, you can run top directly:

$ srun --interactive --pty --jobid=<jobid> top

The -w nid00XXXX option can be added to select a specific compute node to view:

$ srun --interactive --pty --jobid=<jobid> -w nid002217 top