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Difference between revisions of "Terra:Batch Job Files"

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Revision as of 16:54, 21 May 2018

Building Job Files

While not the only method of submitted programs to be executed, job files fulfill the needs of most users.

The general idea behind job files follows:

  • Make resource requests
  • Add your commands and/or scripting
  • Submit the job to the batch system

In a job file, resource specification options are preceded by a script directive. For each batch system, this directive is different. On Terra (Slurm) this directive is #SBATCH.
For every line of resource specifications, this directive must be the first text of the line, and all specifications must come before any executable lines. An example of a resource specification is given below:

#SBATCH --jobname=MyExample  #Set the job name to "MyExample"

Note: Comments in a job file also begin with a # but Slurm recognizes #SBATCH as a directive.

A list of the most commonly used and important options for these job files are given in the following section of this wiki. Full job file examples are given below.

Basic Job Specifications

Several of the most important options are described below. These basic options are typically all that is needed to run a job on Terra.

Basic Terra (Slurm) Job Specifications
Specification Option Example Example-Purpose
Reset Env I --export=NONE Do not propagate environment to job
Reset Env II --get-user-env=L Replicate the login environment
Wall Clock Limit --time=[hh:mm:ss] --time=01:15:00 Set wall clock limit to 1 hour 15 min
Job Name --job-name=[SomeText] --job-name=mpiJob Set the job name to "mpiJob"
Total Task/Core Count --ntasks=[#] --ntasks=16 Request 16 tasks/cores total
Tasks per Node I --ntasks-per-node=# --ntasks-per-node=5 Request exactly (or max) of 5 tasks per node
Memory Per Node --mem=value[K|M|G|T] --mem=32G Request 32 GB per node
Combined stdout/stderr --output=[OutputName].%j --output=mpiOut.%j Collect stdout/err in mpiOut.[JobID]

It should be noted that Slurm divides processing resources as such: Nodes -> Cores/CPUs -> Tasks

A user may change the number of tasks per core. For the purposes of this guide, each core will be associated with exactly a single task.

Optional Job Specifications

A variety of optional specifications are available to customize your job. The table below lists the specifications which are most useful for users of Terra.

Optional Terra/Slurm Job Specifications
Specification Option Example Example-Purpose
Set Allocation --account=###### --account=274839 Set allocation to charge to 274839
Email Notification I --mail-type=[type] --mail-type=ALL Send email on all events
Email Notification II --mail-user=[address] --mail-user=howdy@tamu.edu Send emails to howdy@tamu.edu
Specify Queue --partition=[queue] --partition=gpu Request only nodes in gpu subset
Specify General Resource --gres=[resource]:[count] --gres=gpu:1 Request one GPU per node
Submit Test Job --test-only Submit test job for Slurm validation
Request Temp Disk --tmp=M --tmp=10240 Request at least 10 GB in temp disk space
Request License --licenses=[LicenseLoc] --licenses=nastran@slurmdb:12

Alternative Specifications

The job options within the above sections specify resources with the following method:

  • Cores and CPUs are equivalent
  • 1 Task per 1 CPU desired
  • You specify: desired number of tasks (equals number of CPUs)
  • You specify: desired number of tasks per node (equal or less than the 28 cores per compute node)
  • You get: total nodes equal to #ofCPUs/#ofTasksPerNodes
  • You specify: desired Memory per node

Slurm allows users to specify resources in units of Tasks, CPUs, Sockets, and Nodes.

There are many overlapping settings and some settings may (quietly) overwrite the defaults of other settings. A good understanding of Slurm options is needed to correctly utilize these methods.

Alternative Memory/Core/Node Specifications
Specification Option Example Example-Purpose
Node Count --nodes=[min[-max]] --nodes=4 Spread all tasks/cores across 4 nodes
CPUs per Task --cpus-per-task=# --cpus-per-task=4 Require 4 CPUs per task (default: 1)
Memory per CPU --mem-per-cpu=MB --mem-per-cpu=2000 Request 2000 MB per CPU
Tasks per Core --ntasks-per-core=# --ntasks-per-core=4 Request max of 4 tasks per core
Tasks per Node II --tasks-per-node=# --tasks-per-node=5 Equivalent to Tasks per Node I
Tasks per Socket --ntasks-per-socket=# --ntasks-per-socket=6 Request max of 6 tasks per socket
Sockets per Node --sockets-per-node=# --sockets-per-node=2 Restrict to nodes with at least 2 sockets

If you want to make resource requests in an alternative format, you are free to do so. Our ability to support alternative resource request formats may be limited.

Using Other Job Options

Slurm has facilities to make advanced resources requests and change settings that most Terra users do not need. These options are beyond the scope of this guide.

If you wish to explore the advanced job options, see the Advanced Documentation.

Environment Variables

All the nodes enlisted for the execution of a job carry most of the environment variables the login process created: HOME, SCRATCH, PWD, PATH, USER, etc. In addition, Slurm defines new ones in the environment of an executing job. Below is a list of most commonly used environment variables.

Basic Slurm Environment Variables
Variable Usage Description
Job ID $SLURM_JOBID Batch job ID assigned by Slurm.
Job Name $SLURM_JOB_NAME The name of the Job.
Queue $SLURM_JOB_PARTITION The name of the queue the job is dispatched from.
Submit Directory $SLURM_SUBMIT_DIR The directory the job was submitted from.
Temporary Directory $TMPDIR This is a directory assigned locally on the compute node for the job located at /work/job.$SLURM_JOBID. Use of $TMPDIR is recommended for jobs that use
many small temporary files.

Note: To see all relevant Slurm environment variables for a job, add the following line to the executable section of a job file and submit that job. All the variables will be printed in the output file.

env | grep SLURM

Clarification on Memory, Core, and Node Specifications

Memory Specifications are IMPORTANT.
For examples on calculating memory, core, and/or node specifications on Terra: Specification Clarification.

Executable Commands

After the resource specification section of a job file comes the executable section. This executable section contains all the necessary UNIX, Linux, and program commands that will be run in the job.
Some commands that may go in this section include, but are not limited to:

  • Changing directories
  • Loading, unloading, and listing modules
  • Launching software

An example of a possible executable section is below:

cd $SCRATCH      # Change current directory to /scratch/user/[netID]/
ml purge         # Purge all modules
ml intel/2016b   # Load the intel/2016b module
ml               # List all currently loaded modules

./myProgram.o    # Run "myProgram.o"

For information on the module system or specific software, visit our Modules page and our Software page.