Once you have an executable program and are ready to run it on the compute nodes, you must create a job script that performs the following functions:
- Use job batch options to request the resources that will be needed (i.e. number of processors, run time, etc.), and
- Use commands to prepare for execution of the executable (i.e. cd to working directory, source shell environment files, copy input data to a scratch location, copy needed output off of scratch location, clean up scratch files, etc).
After the job script has been constructed you must submit it to the job scheduler for execution. The remainder of this section will describe the anatomy of a job script and how to submit and monitor jobs.
SLURM Batch Script Options
All jobs must be submitted via a SLURM batch script or invoking sbatch at the command line . See the table below for SLURM submission options.
Required: You need to specify both the name of the account and partition to schedule jobs especially to use a condo on the cluster.
Use the command sacctmgr show assoc user=netID to show which accounts and partitions with which you have access.
Required: Assigns a job name. The default is the name of SLURM job script.
|#SBATCH --ntasks=2||Recommended: The number of tasks per job. Usually used for MPI jobs.|
You can get further explanation here .
Recommended: The number of nodes requested.
Recommended: The number of tasks per node. Usually used in combination with --nodes for MPI jobs.
|#SBATCH --cpus-per-task=4||Recommended: The number processes per task. Usually used for OpenMP or multi-threaded jobs.|
Recommended: Specify the name of the Partition (queue) to use. Use this to specify the default partition or a special partition i.e. non-condo partiton with which you have access.
Recommended: The maximum run time needed for this job to run, in days-hh:mm:ss. If not specified, the default run time will be chosen automatically.
Optional: The maximum amount of physical memory used by any single process of the job ([M]ega|[G]iga|[T]era)Bytes.
See our FAQ for more details.
|#SBATCH --export=ALL||Required: Exports all environment variables to the job. See our FAQ for details.|
|#SBATCH --mail-user=YourEmailAddress||Recommended: Email address for job status messages.|
|#SBATCH --mail-type=ALL||Recommended: SLURM will notify the user via email when the job reaches the following states BEGIN, END, FAIL or REQUEUE.|
|#SBATCH --nodes=1 --exclusive||Optional: Using both of these options will give your job exclusive access to a node such that no other jobs can share the node. |
This combination of arguments will assign eight tasks to your job and will give it exclusive access to all of the resources
(i.e. memory) of the entire node without interference from other jobs. Please see our FAQ for more details on exclusive access.
Optional: The full path for the standard output (stdout) and standard error (stderr) "slurm-%j.out" file, where the "%j" is replaced by the job ID. Current working directory is the default.
Optional: The full path for the standard error (stderr) "slurm-%j.out" files. Use this only when you want to separate (stderr) from (stdout). Current working directory is the default.
Serial Job Script
A job script may consist of SLURM directives, comments and executable statements. A SLURM directive provides a way of specifying job attributes in addition to the command line options. For example, we could create a myjob.slurm script this way:
This example script will submit a job to the default partition using 1 processor and 1GB of memory per processor, with a maximum run time of 30 minutes.
If you need to debug your program and want to run in interactive mode, the same request above could be constructed like this (via the srun command):
For more details on interactive jobs, please see our FAQ on this topic.
SLURM Environment Variables in Job Scripts
When you submit a job, it will inherit several environment variables that are automatically set by SLURM. These environment variables can be useful in your job submission scripts as seen in the examples above. A summary of the most important variables are presented in the table below.
Location of shared scratch space. See our FAQ for more details.
|$LOCAL_SCRATCH||Location of local scratch space on each node.|
Environment variable containing a list of all nodes assigned to the job.
Path from where the job was submitted.
Job Launcher (srun)
For jobs that need two or more processors and are compiled with MPI libraries, you must use srun to launch your job. The job launcher's purpose is to spawn copies of your executable across the resources allocated to your job. We currently support srun for this task and do not support the mpirun or mpiexec launchers. By default srun only needs your executable, the rest of the information will be extracted from SLURM.
The following is an example of how to use srun inside your SLURM batch script. This example will run myMPIprogram as a parallel MPI code on all of the processors allocated to your job by SLURM:
This example script will submit a job to the default partition using 24 processor cores and 1GB of memory per processor core, with a maximum run time of 30 minutes.
The following example will run myMPIprogram on only four processors even if your batch script requested more than four.
To ensure that your job will be able to access an mpi runtime, you must load an mpi module before submitting your job as follows:
Submitting and Monitoring Jobs
Once your job script is ready, use sbatch to submit it as follows:
This will return a jobID number while the output and error stream of the job will be saved to one file inside the directory where the job was submitted, unless you specified otherwise.
The status of the job can be obtained using SLURM commands. See the table below for a list of commands:
Show a detailed list of all submitted jobs.
squeue -j jobID
Show a detailed description of the job given by jobID.
squeue -- start -j jobID
Gives an estimate of the expected start time of the job given by jobID.
There are variations to these commands that can also be useful. They are described below:
Show a list of all running jobs.
squeue -u username
Show a list of all jobs in queue owned by the user specified by username.
scontrol show job jobID
To get a verbose description of the job given by jobID. The output can be used as a template when you are attempting to modify a job.
There are many different states that a job can be after submission: BOOT_FAIL (BF), CANCELLED (CA), COMPLETED (CD), CONFIGURING (CF), COMPLETING (CG), FAILED (F), NODE_FAIL (NF), PENDING (PD), PREEMPTED (PR), RUNNING (R), SUSPENDED (S), TIMEOUT (TO), or SPECIAL_EXIT (SE). The squeue command with no arguments will list all jobs in their current state. The most common states are described below.
Running (R): These are jobs that are running.
Pending (PD): These jobs are eligible to run but there is simply not enough resources to allocate to them at this time.
A job can be deleted by using the scancel command as follows: