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Running applications using SLURM
With SLURM you can specify the tasks that you want to be executed; the system takes care of running these tasks and returns the results to the user. If the resources are full, then SLURM holds your jobs and runs them when they will become available.
With SLURM you create a batch job which you then submit to the scheduler. A batch job is a file (a shell script under UNIX) containing the set of commands that you want to run. It also contains the directives that specify the characteristics (attributes) of the job and the resource requirements (e.g. number of processors and CPU time) that your job needs.
Once you create your job, you can reuse it if you wish. Or, you can modify it for subsequent runs.
For example, here is a simple SLURM job script to run a user's application by setting a limit (one hour) to the maximum wall clock time, requesting 1 full node with 36 cores:
#!/bin/bash
#SBATCH --nodes=1 # 1 node
#SBATCH --ntasks-per-node=36 # 36 tasks per node
#SBATCH --time=1:00:00 # time limits: 1 hour
#SBATCH --error=myJob.err # standard error file
#SBATCH --output=myJob.out # standard output file
#SBATCH --account=<account_no> # account name
#SBATCH --partition=<partition_name> # partition name
#SBATCH --qos=<qos_name> # quality of service
./my_application
SLURM has been configured differently on the various systems reflecting the different system features. Please refer to the system specific guides for more detailed information.
Basic SLURM commands
The main user's commands of SLURM are reported in the table below: please consult the man pages for more information.
| sbatch, srun, salloc | Submit a job |
| squeue | Lists jobs in the queue |
| sinfo | Prints queue information about nodes and partitions |
| sbatch batch script | Submits a batch script to the queue |
| scancel jobid | Cancel a job from the queue |
| scontrol hold jobid | Puts a job on hold in the queue. |
| scontrol release | Releases a job from hold |
| scontrol update | Change attributes of submitted job. |
| scontrol requeue | Requeue a running, suspended or finished Slurm batch job into pending state. |
| scontrol show job jobid | Produce a very detailed report for the job. |
| sacct -k, --timelimit-min | Only send data about jobs with this time limit. |
| sacct -A account_list | Display jobs when a comma separated list of accounts are given as the argument. |
| sstat | Display information about CPU, Task, Node, Resident Set Size and Virtual Memory |
| sshare | Display information about shared for a user, a repo, a job, a partition, etc. |
| sprio | Display information about a job's scheduling priority from multi-factor priority components. |
Submit a job:
> sbatch [opts] job_script > salloc --nodes=<nodes_no> --ntasks-per-node=<tasks_per_node_no> --account=<account_no> --partition=<name> <command> (interactive job)
The second command is related to a so-called "Interactive job": with salloc the user allocates a set of resources (nodes). The job is queued and scheduled as any SLURM batch job, but when executed, the standard input, output, and error streams of the job are connected to the terminal session in which salloc is running. When the job begins its execution, all the input to the job is taken from the terminal session. You can use CTRL-D or "exit" to close the session.
if you specify a command at the end of your salloc string (like "./myscript"), the job will simply execute the command and close, prompting the standard output and error directly on your working terminal.
WARNING: interactive jobs with SLURM are more delicate than with PBS. With salloc, your prompt won't tell you that you are working on a compute node, so it can be easy to forget that there is an interactive job running. Furthermore, deleting the job with "scancel" while inside the job itself will not boot you out of the nodes, and will invalid your interctive interactive session because every command is searching for a jobid that doesn't exist anymore. If you are stuck in this situation, you can allways always revert back to your original front-end session with "CTRL-D" or "exit".
Displaying Job Status:
> squeue (lists all jobs)
> squeue -u $USER (lists only jobs submitted by you)> squeue --job <job_id> (only the specified job)> squeue --job <job_id> -l (full display of the specified job)
> scontrol show job <job_id> (detailed informations about your job)
Displaying Queue Status:
sinfo displays information about nodes and partitions (queues).
It offers several options - here is a formate template that you may find useful. To view a complete list of all options and their descriptions, use man sinfo, or access SchedMD webpage on sinfo.
- Display a straight-forward summary: available partitions, their status, timelimit, node information with A/I/O/T ( allocated, idle, other, total ) and specifications S:C:T (sockets:cores:threads)
> sinfo -o "%20P %10a %10l %15F %10z"
Numbers represent field length and should be used to properly accommodate the data.
> sinfo
> sinfo -p <partition> (Long format of the specified partition)
> sinfo -d (Information about the offline nodes. The list of available partition is also easier to read)
--all Displays more details
-d Display all partions partitions with their time limit and dead nodes
-p Display details for the specific partition eg: sinfo -p bdw_usr_prod
-i < n > "Top like" display, iterates every "n" seconds.
-l, --long Displays several additional information, such as the reason why specific nodes are down/drained.
For a long detailed report, this option is best used together with -N. eg: sinfo -N -l
-n <node> Can be used to view information about a specific node. eg: sinfo -N -n r033c01s01
Delete a job:
> scancel <jobID>
More information about these commands are is available with the man command.
The User Environment
There are a number of environment variables provided to the SLURM job. Some of them are taken from the user's environment and carried with the job. Others are created by SLURM.
All SLURM-provided environment variable names start with the characters SLURM_.
Below are listed some of the more useful variables, and some typical values taken as an example:
SLURM_JOB_NAME=job SLURM_NNODES (or SLURM_JOB_NUM_NODES)=2 SLURM_JOBID (or SLURM_JOB_ID)=453919 SLURM_JOB_NODELIST=node1,node2,... SLURM_SUBMIT_DIR=/marconi_scratch/userexternal/username SLURM_SUBMIT_HOST=node1 SLURM_CLUSTERNAME=cluster1 SLURM_JOB_PARTITION=partition1
There are a number of ways that you can use these environment variables to make more efficient use of SLURM. For example example, SLURM_JOB_NAME can be used to retrieve the SLURM jobname. Another commonly used variable is SLURM_SUBMIT_DIR which contains the name of the directory from which the user submitted the SLURM job.
WARNING: $SLURM_JOB_NODELIST will display the node names in contracted forms, meaning that for consecutive nodes you will get their range instead of the full list. You will see in square brackets the ID of the first and the last node of the chunk, meaning that all the nodes between them are also part of the actual node listnode of the chunk, meaning that all the nodes between them are also part of the actual node list.
Job TMPDIR:
When a job starts, a temporary area is defined on the storage local to each compute node:
TMPDIR=/scratch_local/slurm_job.$SLURM_JOB_ID
which can exclusively be used only by the job's owner. During your jobs, you can access the area with the (local) variable $TMPDIR. The directory is removed at the end of the job, hence remember to save the data stored in such area to a permanent directory. Please note that the area being on local disks, it can be accessed only by the processes running on the node. For multinode jobs, if you need all the processes to access some data, please use the shared filesystems $HOME, $WORK, $CINECA_SCRATCH.
SLURM Resources
A job requests resources through the SLURM syntax; SLURM matches requested resources with available resources, according to the rules defined by the administrator. When the resources are allocated to the job, the job can be executed.
There are different types of resources, i.e. server level resources, like walltime, and chunk resources, like number of cpus or nodes. Other resources may be added to manage access to software resources, for example when resources are limited and the lack of availability leads to jobs abort when they are scheduled for execution. More details may be found in the module help of the application you are trying to execute.
The syntax of the request depends on the type of the resource:
#SBATCH --<resource>=<value> (server level resources, e.g. walltime) #SBATCH --<chunk_resource>=<value> (chunk resources, e.g. cpus, nodes,...)
For example:
#SBATCH --time=10:00:00 #SBATCH --ntasks-per-node=1
Resources can be required either:
1) using SLURM directives in the job script
2) using options of the sbatch sbatch/salloc command
SLURM job script
A SLURM job script consists of:
- An optional shell specification
- SLURM directives
- Tasks -- programs or commands to be executed
Once ready, the job must be submitted to SLURM:
> sbatch [options] <name of script>
The shell to be used by SLURM is defined in the first line of the job script (mandatory!):
#!/bin/bash (or #!/bin/sh)
The SLURM directives are used to request resources or set attributes. A directive begins with the default string #SBATCH. One or more directives can follow the shell definition in the job script.
The tasks can be programs or commands. This is where the user specifies the application to run.
SLURM directives
The type of resources required for a serial or parallel MPI/OpenMP/mixed job must be specified with a SLURM directive:
#SBATCH --<resource_spec>=<value>
where <resource_spec> can be one of the following:
- --nodes=NN number of nodes
- --ntasks-per-node=CC number of tasks/processes per node
- --cpus-per-task=TT number of threads/cpus per task
For example for a MPI or MPI/OpenMP mixed job (2 MPI processes and 8 threads):
#SBATCH --nodes=2
#SBATCH --ntasks-per-node=8
For a serial job for example:
#SBATCH --nodes=1
#SBATCH --ntasks-per-node=1
Please note that hyper-threading is enabled on Marconi-A2, so it is possible to increase the number of threads per process up to 4 threads per physical core. For example:
#SBATCH --nodes=2
#SBATCH --ntasks-per-node=34
#SBATCH --cpus-per-task=2
export OMP_NUM_THREADS=8
In the example above, the 68 cores of a KNL node are organized so that the MPI tasks are 34, and two physical cores for each task are set to be OpenMP threads. By increasing the value of OMP_NUM_THREADS to 8, each core is forced to behave as 4 virtual threads, thus exploiting the characteristics of hyper-threading. However, the above configuration doesn't guarantee that the OpenMP threads are allocated on convenient positions among the node (i.e. the 2 cpus per task, governing 4 threads each, may be too far from each other).
In terms of a safer distribution and therefore a better performance, a configuration like this can be prefered:
#SBATCH --nodes=2 #SBATCH --ntasks-per-node=68 #SBATCH --cpus-per-task=1 export OMP_NUM_THREADS=4
SLURM directives: processing time
Resources such as computing time must be requested by this syntax:
#SBATCH --time=<value>
where <value> expresses the actual elapsed time (wall clock) in the format hh:mm:ss
for example:
#SBATCH --time=1:00:00 (one hour)
Please note that there are specific limitations on the maximum walltime on a system. Check , also depending on the partition. Check the system specific guide for more informationsinformation.
SLURM directives: memory allocation
The default memory depends on the partition/queue you are working with. You can specify the requested memory with the --mem=<value> directive up to to maximum memory available on the nodes.
#SBATCH --mem=10000
The default measurement unit for memory requests is the Megabyte (in the example above, we are requesting for 10000MB per node). It is possible to ask for an amount of memory expressed in GB, like this:
#SBATCH --mem=10GB
However, the default request method in MB is preferable, since the memory limits defined for any partition are expressed in this these terms. For example, Marconi SkyLake partition has 182000 182000MB as a limit, corresponding to approx. 177GB.
Please note: if you are requiring a larger memory with respect to the "main amount" on for the system, the number of "effective cores" and the cost of your job could increase. For more information check the accounting section.
SLURM directives: MPI tasks/OpenMP threads affinity
You may have to modify the default affinity, in order to ensure optimal performances on A2 and A3 Marconi.
The slurm directives that concern the processes binding are the following:
--cpu-bind=<cores|threads>
--cpus-per-task=<physical or logical cpus number to allocate for single task>
In order to modify them correctly, we suggest to follow our guidelines.
Other SLURM directives
#SBATCH --account=<account_no> --> name of the project to be accounted to ("saldo -b" for a list of projects)
#SBATCH --job-name=<name> --> job name
#SBATCH --partition=<destination> --> partition/queue destination. For a list and description of available partitions, please refer to the specific cluster description of the guide.
#SBATCH --qos=<qos_name> --> quality of service. Please refer to the specific cluster description of the guide.
#SBATCH --output=<out_file> --> redirects output file (default, if missing, is slurm-<Pid> containing merged output and error file)
#SBATCH --error=<err_file> --> redirects error file (as above)
#SBATCH --mail-type=<mail_events> --> specify email notification (NONE, BEGIN, END, FAIL, REQUEUE, ALL)
#SBATCH --mail-user=<user_list> --> set email destination (email address)Directives in contracted form
Some SLURM directives can be written with a contracted syntax. Here are all the possibilities:
#SBATCH -N <NN> --> #SBATCH --nodes=<NN>
#SBATCH -c <TT> --> #SBATCH --cpus-per-task=<TT>
#SBATCH -t <value> --> #SBATCH --time=<value>
#SBATCH -A <account_no> --> #SBATCH --account=<account_no>
#SBATCH -J <name> --> #SBATCH --job-name=<name>
#SBATCH -p <destination> --> #SBATCH --partition=<destination>
#SBATCH -q <qos_name> --> #SBATCH --qos=<qos_name>
#SBATCH -o <out_file> --> #SBATCH --output=<out_file>
#SBATCH -e <err_file> --> #SBATCH --error=<err_file>
Note: the directives --mem, --mail-type, --mail-user and --ntasks-per-node can't be contracted. About the latter, it exists a SLURM directive "-n" for the number of tasks, but it can be misleading since it is used to indicate the TOTAL number of tasks and not the number of tasks per node. Therefore, it is not recommended since it can lead to confusion and unexpected behaviourbehavior. Use of the uncontracted --ntasks-per-node is recommended instead.
Job
submission and sbatch attributessubmission
When the jobscript job script is ready, you can submit it with the command:
> sbatch <name of script>
The job will be queued by SLURM worload workload manager and will be executed when the requested resources will become available.
Using sbatch attributes to assign job attributes and resource request
It is Is it also possible to assign the job attributes using the sbatch command options:
> sbatch [--job-name=<name>] [--partition=<queue/partition>] [--out=<out_file>] [--err=<err_file>] [--mail-type=<mail_events>] [--mail-user=<user_list>] <name of script>
And the resources can also be requested using the sbatch command options:
> sbatch [--time=<value>] [-ntasks=<value>] [--account=<account_no>] <name of script>
The sbatch command options override script directives , if present.
Examples
Serial job script
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The account number (#SBATCH --account) is required to specify the project to be accounted for. To find out the list of your account number/s, please use the "saldo -b" command.
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