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Specifying job requirements

We now describe several statements that are most commonly used to specify resource requirements for all kinds of jobs. Refer to “man sbatch” for more information.

Walltime (reqeuested job time)

The walltime attribute specifies the time requested for completing the job. The time is not CPU-time but the total time measured by an ordinary clock. In the previous example, the time requested was 0 hours 5 minutes and 0 seconds. Walltime is specified in seconds or using the following notation:


If your calculation hasn’t finished once the specified time has elapsed, SLURM will terminate your job. It is, therefore good practise** to specify a bit more time than you anticipate your job to take. This ensures that you still get your results, even if the job is slowed by some interference, e.g. waiting for a write to a shared file system to finish. However, don’t specify excessive amounts of extra time. Due to scheduling constraints, jobs asking for less time will typically spend less time in the queue, waiting for their execution. This also provides safety against the depletion of your allocation. If e.g., your job hangs, SLURM will terminate your job and the project will be charged less time if the walltime margin is not excessive.

To specify your walltime requirements write a statement like

#SBATCH -t 00:10:00

into your job script.

The maximum walltime for any job on COSMOS is 168h (7 days).

Naming jobs

All jobs are given both a job identifier and a name for easier identification in the batch system. The default name given to a job is the file name of the submit script, making it difficult to identify your job if you use a common name for your submit scripts. You can give your job a name from inside the script by using the -J option:

#SBATCH -J parameterTest

This will name your job “parameterTest”.

Specifying memory requirements

The COSMOS system has 256 GB of memory installed on a normal compute node. To allow memory for the operating system, only 254000 MB are available for jobs and the default memory request per core is 5300 MB of memory (48 cores per node). If more than 5300 MB per core is needed, it has to be requested explicitly using the --mem-per-cpu option. For example, if you require 10000 MB per core, add the line:

#SBATCH --mem-per-cpu=10000

When requesting more than 5300 MB per processing core on a normal COSMOS node, your jobs will be charged at a higher rate. If you do this, some processing cores must remain idle since you use more than your fair share of memory.

Controlling job output

By default, the output which your job writes to standard output (stdout) and standard error (stderr) is written to a file named


The %j in the file name will be replaced by the jobnumber SLURM assigns to your job. This ensures that the output file from your job is unique and that different jobs do not interfere with each other's output files.

In many cases, the default file name is not convenient. You might want to have a file name which is more descriptive of the job that is actually running - you might even want to include important meta-data, such as physical parameters, into the output filename(s). This can be achieved by using the -o and -e options of sbatch. The -o option specifies the file containing the stdout and the -e option the file containing the stderr. It is good practise to include the %j string into the filenames. That will prevent jobs from overwriting each other's output files. The following gives an example:

#SBATCH -o calcflow_m1_%j.out
#SBATCH -e calcflow_m1_%j.err


You can give the same filename for both options to get stdout and stderr written to the same file.

Job notification emails

SLURM on the systems can send you an email if the status of your job changes as it progresses through the job queue. To use this feature, you need to specify the email address using the --mail-user option and specify the event you want to get notified about using the --mail-type option. The following

#SBATCH --mail-type=END

will send an email to the address once the job has ended. Valid type values, selecting the event you can get notified about, are BEGIN, END, FAIL, REQUEUE, and ALL (any state change).


If messages do not arrive, please monitor your junkmail or spam folder.

Job dependencies

To describe job dependencies, use the -d option of sbatch. This is particularly useful for job dependencies, in workflows.

To illustrate this consider the following example. You require a serial job to create a mesh for your simulation. Once this has finished, you want to start a parallel job using the mesh. You first submit the mesh creation job using sbatch

[fred@cosmos-dt Simcode]$ sbatch
Submitted batch job 8042

As discussed, sbatch returns you a jobid, 8042 in this example. You use this to declare your dependency when submitting the simulation job to the queue

[fred@cosmos-dt Simcode]$ sbatch -d afterok:8042
Submitted batch job 8043

When using jobinfo or squeue to monitor job 8043, this should now be in status pending (PD) with the reason of dependency. Another common use case for this functionality is a simulation requiring many days of computer times being split into several submissions.

Testing jobs (test queue)

To run short tests, it is possible to request extra high priority on COSMOS with the help of

#SBATCH --qos=test

For one such job, the maximum walltime is 1 h and the maximum number of nodes is two and a user is only allowed to run two such jobs simultaneously. A system of floating reservations is used to free two nodes every second hour between 8.00 and 20.00 to reduce the queue time for test jobs. The way it works also means that the shorter the test job, the more likely it is to start sooner rather than later. It is not allowed to use qos=test for a series of production runs.

Controlling requeueing/restarting of jobs

By default, the scheduler will requeue (aka. restart) jobs that suffered from node failure. This is not always desirable. Adding a line

#SBATCH --no-requeue

to the header portion of your job script prevents this behavior.

Specifying a project allocation and partition

Most users are members of a single LU project. These users do not need to specify a project in their submission script. The LUNARC set-up will automatically use that project for accounting.

Users with membership in more than one project have to let the system know which project to charge for the run. To do so, you need to specify the project using the -A option:

#SBATCH -A lu2022-x-xxx

Replace the lu2022-x-xx with the string naming your project. The correct name can be obtained by using the projinfo command. The information is also available in the SUPR system, but notice the difference in the formatting of the names.

In addition, for those who access private nodes (financed by a research project) through an LU project, the corresponding reservation has to be stated:

#SBATCH --reservation=lu2022-x-xx

Accessing GPUs in the LU-partition

Some compute nodes in the Lund University partition are equipped with GPUs.

Information on accessing the GPUs will be available shortly

Author: (LUNARC)

Last Updated: 2024-02-12