UVA ✎ compute_slurm [Computer Science Support Wiki]

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====== SLURM ======

The Computer Science Department uses a resource management system called [[https://en.wikipedia.org/wiki/Slurm_Workload_Manager|SLURM]].  The purpose of a workload scheduler such as SLURM is to allocate computational resources to our users in such a way that everyone gets their fair share of execution time.

===== Note on Modules in Slurm =====

Due to the way sbatch spawns a bash session (non-login session), some init files are not loaded from ''%%/etc/profile.d%%''.  This prevents the initialization of the [[linux_environment_modules|Environment Modules]] system and will prevent you from loading software modules.

To fix this, simply include the following line in your sbatch scripts:

<code bash>
source /etc/profile.d/modules.sh
</code>

===== Using SLURM =====

==== Information Gathering ====

SLURM provides a set of tools to use for interacting with the scheduling system.  To view information about compute nodes in the SLURM system, we can use the command ''%%sinfo%%''.

<code>
ktm5j@power1 ~ $ sinfo
PARTITION     AVAIL  TIMELIMIT  NODES  STATE NODELIST
main*            up   infinite     37   idle hermes[1-4],artemis[1-7],slurm[1-5],nibbler[1-4],trillian[1-3],granger[1-6],granger[7-8],ai0[1-6]
qdata            up   infinite      8   idle qdata[1-8]
qdata-preempt    up   infinite      8   idle qdata[1-8]
falcon           up   infinite     10   idle falcon[1-10]
intel            up   infinite     24   idle artemis7,slurm[1-5],granger[1-6],granger[7-8],nibbler[1-4],ai0[1-6]
amd              up   infinite     13   idle hermes[1-4],artemis[1-6],trillian[1-3]
</code>

With ''%%sinfo%%'' we can see a listing of what SLURM calls partitions and a list of nodes associated with these partitions.  A partition is a grouping of nodes, for example our //main// partition is a group of all SLURM nodes that are not reserved and can be used by anyone.  Notice that hosts can be listed in several different partitions..  For example, ''%%slurm[1-5]%%'' can be found in both the //main// and //intel// partitions.  //Intel// is a partition of systems with Intel processors, likewise the hosts in //amd// have AMD processors.

To view jobs running on the queue, we can use the command ''%%squeue%%''.  Say we have submitted one job to the main partition, running ''%%squeue%%'' will look like this:

<code>
ktm5j@power1 ~ $ squeue
             JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
            467039      main    sleep    ktm5j  R       0:06      1 artemis1
</code>

and now that a node has been allocated, that node ''%%artemis1%%'' will show as //alloc// in ''%%sinfo%%''

<code>
ktm5j@power1 ~ $ sinfo
PARTITION     AVAIL  TIMELIMIT  NODES  STATE NODELIST
main*            up   infinite     37   idle hermes[1-4],artemis[2-7],slurm[1-5],nibbler[1-4],trillian[1-3],granger[1-6],granger[7-8],ai0[1-6]
main*            up   infinite      1  alloc artemis1
qdata            up   infinite      8   idle qdata[1-8]
qdata-preempt    up   infinite      8   idle qdata[1-8]
falcon           up   infinite     10   idle falcon[1-10]
intel            up   infinite     24   idle artemis7,slurm[1-5],granger[1-6],granger[7-8],nibbler[1-4],ai0[1-6]
amd              up   infinite     13   idle hermes[1-4],artemis[1-6],trillian[1-3]
</code>

==== Jobs ====

To use SLURM resources, you must submit your jobs (program/script/etc.) to the SLURM controller.  The controller will then send your job to compute nodes for execution, after which time your results will be returned.

Users can submit SLURM jobs from any of the power servers: ''%%power1%%''-''%%power6%%''.  From a shell, you can submit jobs using the commands [[https://slurm.schedmd.com/srun.html|srun]] or [[https://slurm.schedmd.com/sbatch.html|sbatch]].  Let's look at a very simple example script and ''%%sbatch%%'' command.

Here is our script, all it does is print the hostname of the server running the script.  We must add ''%%SBATCH%%'' options to our script to handle various SLURM options.

<code bash>
#!/bin/bash

#SBATCH --job-name="Slurm Simple Test Job" #Name of the job which appears in squeue
#
#SBATCH --mail-type=ALL
#SBATCH --mail-user=ktm5j@virginia.edu
#
#SBATCH --error="my_job.err"                    # Where to write std err
#SBATCH --output="my_job.output"                # Where to write stdout
#SBATCH --nodelist=slurm1

hostname
</code>

Let's put this in a directory called ''%%slurm-test%%'' in our home directory.  We run the script with ''%%sbatch%%'' and the results will be put in the file we specified with ''%%--output%%''.  If no output file is specified, output will be saved to a file with the same name as the SLURM jobid.

<code>
ktm5j@power3 ~ $ cd slurm-test/ 
ktm5j@power3 ~/slurm-test $ chmod +x test.sh 
ktm5j@power3 ~/slurm-test $ sbatch test.sh 
Submitted batch job 466977
ktm5j@power3 ~/slurm-test $ ls
my_job.err  my_job.output  test.sh
ktm5j@power3 ~/slurm-test $ cat my_job.output 
slurm1
</code>

Here is a similar example using ''%%srun%%'' running on multiple nodes:

<code>
ktm5j@power3 ~ $ srun -w slurm[1-5] -N5 hostname
slurm4
slurm1
slurm2
slurm3
slurm5
</code>

==== Terminating Jobs ====

Please be aware of jobs you start and make sure that they finish executing.  If your job does not converge, it will sit in the queue taking up resources and preventing others from running their jobs.

To cancel a running job, use the ''%%scancel [jobid]%%'' command

<code>
ktm5j@power1 ~ $ squeue
             JOBID PARTITION     NAME     USER ST       TIME  NODES NODELIST(REASON)
            467039      main    sleep    ktm5j  R       0:06      1 artemis1           <--  Running job
ktm5j@power1 ~ $ scancel 467039
</code>

==== Partitions ====

Slurm refers to job queues as //partitions//.  These queues can have unique constraints such as compute nodes, max runtime, resource limits, etc.  There is a ''%%main%%'' queue, which will make use of all non-GPU compute nodes.

Partition is indicated by ''%%-p partname%%'' or ''%%--partition partname%%''.

To specify a partition with ''%%sbatch%%'' file:

<code>
#SBATCH --partition=gpu
</code>

Or from the command line with ''%%srun%%''

<code>
-p gpu
</code>

An example running the command ''%%hostname%%'' on the //intel// partition, this will run on any node in the partition:

<code>
srun -p intel hostname
</code>

==== GPUs ====

Slurm handles GPUs and other non-CPU computing resources using what are called [[https://slurm.schedmd.com/gres.html|GRES]] Resources (Generic Resource).  To use the GPU(s) on a system using Slurm, either using ''%%sbatch%%'' or ''%%srun%%'', you must request the GPUs using the ''%%--gres:x%%'' option.  You must specify the ''%%gres%%'' flag followed by ''%%:%%'' and the quantity of resources

Say we want to use 4 GPUs on a system, we would use the following ''%%sbatch%%'' option:

<code>
#SBATCH --gres=gpu:4
</code>

Or from the command line 

<code>
--gres=gpu:4
</code>

==== Interactive Shell ====

We can use ''%%srun%%'' to spawn an interactive shell on a SLURM compute node.  While this can be useful for debugging purposes, this is **not** how you should typically use the SLURM system.  To spawn a shell we must pass the ''%%--pty%%'' option to ''%%srun%%'' so output is directed to a pseudo-terminal:

<code>
ktm5j@power3 ~/slurm-test $ srun -w slurm1 --pty bash -i -l -
ktm5j@slurm1 ~/slurm-test $ hostname
slurm1
ktm5j@slurm1 ~/slurm-test $
</code>

The ''%%-i%%'' argument tells ''%%bash%%'' to run as interactive.  The ''%%-l%%'' arg instructs bash that this is a login shell, this, along with the final ''%%-%%'' are important to reset environment variables that otherwise might cause issues using [[linux_environment_modules|Environment Modules]]

===== Reservations =====

Reservations for specific resources or nodes can be made by submitting a request to <cshelpdesk@virginia.edu>.  For more information about using reservations, see the main article on [[compute_slurm_reservations|SLURM Reservations]]