SRUN(1)

." $Id$

NAME
srun - run parallel jobs

SYNOPSIS
srun [OPTIONS...] executable [args...]
srun --batch [OPTIONS...] job_script
srun --allocate [OPTIONS...] [job_script]
srun --attach=jobid

DESCRIPTION
Allocate resources and optionally initiate parallel jobs on clusters managed by SLURM.

parallel run options

-n, --nprocs=nprocs
    Specify the number of processes to run. Request that srun allocate nprocs processes. Specification of the number of processes per node may be achieved with the -c and -N options. The default is one process per node unless -c explicitly specifies otherwise.

-c, --cpus-per-task=ncpus
    Request that ncpus be allocated per process. This may be useful if the job is multithreaded and requires more than one cpu per task for optimal performance. The default is one cpu per process.

-N, --nodes=nnodes
    Request that nnodes nodes be allocated to this job. nnodes may be either a specific number or a minimum and maximum node count separated by a hyphen (e.g. "--nodes=2-4"). The partition's node limits supersede those of the job. If a job's node limits are completely outside of the range permitted for it's associated partition, the job will be left in a PENDING state. Note that the environment variable SLURM_NNODES will be set to the count of nodes actually allocated to the job. See the ENVIRONMENT VARIABLES section for more information. The default is to allocate one cpu per process, such that nodes with one cpu will run one process, nodes with 2 cpus will be allocated 2 processes, etc. The distribution of processes across nodes may be controlled using this option along with the -n and -c options.

-p, --partition=partition
    Request resources from partition "partition." Partitions are created by the slurm administrator.

-t, --time=minutes
    Establish a time limit to terminate the job after the specified number of minutes. If the job's time limit exceed's the partition's time limit, the job will be left in a PENDING state. The default value is the partition's time limit. When the time limit is reached, the job's processes are sent SIGXCPU followed by SIGKILL. The interval between signals is specified by the SLURM configuration parameter KillWait.

--cddir=path
    have the remote processes do a chdir to path before beginning execution. The default is to chdir to the current working directory of the srun process.

-I, --immediate
    exit if resources are not immediately available. By default, --immediate is off, and srun will block until resources become available.

-k, --no-kill
    Do not automatically terminate a job of one of the nodes it has been allocated fails. The job will assume all responsibilities for fault-tolerance. The default action is to terminate the job upon node failure.

-s, --share
    The job can share nodes with other running jobs. This may result in faster job initiation and higher system utilization, but lower application performance.

-O, --overcommit
    overcommit resources. Normally, srun will not allocate more than one process per cpu. By specifying --overcommit you are explicitly allowing more than one process per cpu. However no more than MAX_TASKS_PER_NODE tasks are permitted to execute per node.

-T, --threads=nthreads
    Request that srun use nthreads to initiate and control the parallel job. The default value is the smaller of 10 or the number of nodes allocated.

-l, --label
    prepend task number to lines of stdout/err. Normally, stdout and stderr from remote tasks is line-buffered directly to the stdout and stderr of srun The --label option will prepend lines of output with the remote task id.

-u, --unbuffered
    do not line buffer stdout from remote tasks. This option cannot be used with --label.

-m, --distribution=(block|cyclic)
    Specify an alternate distribution method for remote processes.

    block
        The block method of distribution will allocate processes in-order to the cpus on a node. This is the default behavior if the number of tasks exceeds the number of nodes requested.

    cyclic
        The cyclic method distributes processes in a round-robin fashion across the allocated nodes. That is, process 1 will be allocated to the first node, process 2 to the second, and so on. This is the default behavior if the number of tasks is no larger than the number of nodes requested.

-J, --job-name=jobname
    Specify a name for the job. The specified name will appear along with the job id number when querying running jobs on the system. The default is the supplied executable program's name.

-o, --output=mode
    Specify the mode for stdout redirection. By default, srun collects stdout from all tasks and line buffers this output to the attached terminal. With --output stdout may be redirected to a file, to one file per task, or to /dev/null. See section IO Redirection below for the various forms of mode.

-i, --input=mode
    Specify how stdin is to redirected. By default, srun redirects stdin from the terminal all tasks. See IO Redirection below for more options.

-e, --error=mode
    Specify how stderr is to be redirected. By default, srun redirects stderr to the same file as stdout, if one is specified. The --error option is provided to allow stdout and stderr to be redirected to different locations. See IO Redirection below for more options.

-b, --batch
    Submit in "batch mode." srun will make a copy of the executable file (a script) and submit the request for execution when resouces are available. srun will terminate after the request has been submitted. The executable file will run on the first node allocated to the job and must contain srun commands to initiate parallel tasks. stdin will be redirected from /dev/null, stdout and stderr will be redirected to a file (default is jobname.out or jobid.out in current working directory, see -o for other IO options). executable must be specified using either a fully qualified pathname or its pathname will be relative to the current working directory. The search path will not be used to locate the file. executable will be interpreted by the user's default shell unless the file begins with "#!" followed by the fully qualified pathname of a valid shell.

-v, --verbose
    verbose operation. Multiple -v's will further increase the verbosity of srun.

-d, --slurmd-debug=level
    Specify a debug level for slurmd(8). level may be an integer value between 0 [quiet, only errors are displayed] and 5 [insanely verbose operation]. The slurmd debug information is copied onto the stderr of the job.

-W, --wait=seconds
    Specify how long to wait after the first task terminates before terminating all remaining tasks. The default value is unlimited. This can be useful to insure that a job is terminated in a timely fashion in the event that one or more tasks terminate prematurely.

Allocate options:

-A, --allocate
    allocate resources and spawn a shell. When --allocate is specified to srun , no remote tasks are started. Instead a subshell is started that has access to the allocated resources. Multiple jobs can then be run on the same cpus from within this subshell. See Allocate Mode below.

Attach to running job:

-a, --attach=id
    This option will attach srun to a running job with job id = id. Provided that the calling user has access to that running job, stdout and stderr will be redirected to the current session and signals received by srun will be forwarded to the remote processes.

-j, --join
    Join with running job. This will duplicate stdout/stderr to the calling srun. stdin and signals will not be propagated to the job. --join is only allowed with --attach.

-s, --steal
    Steal the connection to the running job. This will close any open sessions with the specified job and allow stdin and signals to be propagated. --steal is only allowed with --attach.

Constraint Options. The following options all put constraints on the nodes that may be considered for the job:

--mincpus=n
    Specify minimum number of cpus per node.

--mem=MB
    Specify a minimum amount of real memory.

--vmem=MB
    Specify a minimum amount of virtual memory.

--tmp=MB
    Specify a minimum amount of temporary disk space.

-C, --constraint=list
    Specify a list of constraints. The list of constraints is a comma separated list of features that have been assigned to the nodes by the slurm administrator. If no nodes have the requested feature, then the job will be rejected by the slurm job manager.

--contiguous
    Demand a contiguous range of nodes. The default is "yes". Specify --contiguous=no if a contiguous range of nodes is not a constraint.

-w, --nodelist=host1,host2,... or filename
    Request a specific list of hosts. The job will contain at least these hosts. The list may be specified as a comma-separated list of hosts, a range of hosts (host[1-5,7,...] for example), or a filename. The host list will be assumed to be a filename if it contains a "/" character.

-x, --exclude=host1,host2,... or filename
    Request that a specific list of hosts not be included in the resources allocated to this job. The host list will be assumed to be a filename if it contains a "/"character.

Help options

-?, --help
    Show this help message

--usage
    Display brief usage message

Other options

-V, --version
    output version information and exit

Unless the -a (--attach) or -A (--allocate) options are specified (see Allocate mode and Attaching to jobs below), srun will submit the job request to the slurm job controller, then initiate all processes on the remote nodes. If the request cannot be met immediately, srun will block until the resources are free to run the job. If the -I (--immediate) option is specified srun will terminate if resources are not immediately available.

When initiating remote processes srun will propagate the current working directory, unless --cddir=path is specified, in which case path will become the working directory for the remote processes.

The -n, -c, and -N options control how CPUs and nodes will be allocated to the job. When specifying only the number of processes to run with -n, a default of one CPU per process is allocated. By specifying the number of CPUs required per task (-c), more than one CPU may be allocated per process. If the number of nodes is specified with -N, srun will attempt to allocate at least the number of nodes specified.

Combinations of the above three options may be used to change how processes are distributed across nodes and cpus. For instance, by specifying both the number of processes and number of nodes on which to run, the number of processes per node is implied. However, if the number of CPUs per process is more important then number of processes (-n) and the number of CPUs per process (-c) should be specified.

srun will refuse to allocate more than one process per CPU unless --overcommit (-O) is also specified.

srun will attempt to meet the above specifications "at a minimum." That is, if 16 nodes are requested for 32 processes, and some nodes do not have 2 CPUs, the allocation of nodes will be increased in order to meet the demand for CPUs. In other words, a minimum of 16 nodes are being requested. However, if 16 nodes are requested for 15 processes, srun will consider this an error, as 15 processes cannot run across 16 nodes.

IO Redirection

By default stdout and stderr will be redirected from all tasks to the stdout and stderr of srun , and stdin will be redirected from the standard input of srun to all remote tasks. This behavior may be changed with the --output, --error, and --input (-o, -e, -i) options. Valid format specifications for these options are

all stdout stderr is redirected from all tasks to srun. stdin is broadcast to all remote tasks. (This is the default behavior)

none
    stdout and stderr is not received from any task. stdin is not sent to any task (stdin is closed).

taskid
    stdout and/or stderr are redirected from only the task with relative id equal to taskid, where 0 <= taskid <= ntasks, where ntasks is the total number of tasks in the current job step. stdin is redirected from the stdin of srun to this same task.

filename
    srun will redirect stdout and/or stderr to the named file from all tasks. stdin will be redirected from the named file and broadcast to all tasks in the job.

format string
    srun allows for a format string to be used to generate the named IO file described above. The following list of format specifiers may be used in the format string to generate a filename that will be unique to a given jobid, stepid, node, or task. In each case, the appropriate number of files are opened and associated with the corresponding tasks.

    %J  jobid.stepid of the running job. (e.g. "128.0")

    %j  jobid of the running job.

    %s  stepid of the running job.

    %N  short hostname. This will create a separate IO file per node.

    %n  Node identifier relative to current job (e.g. "0" is the first node of the running job) This will create a separate IO file per node.

    %t  task identifier (rank) relative to current job. This will create a separate IO file per task.

    A number placed between the percent character and format specifier may be used to zero-pad the result in the IO filename. This number is ignored if the format specifier corresponds to non-numeric data (%N for example). Some examples of how the format string may be used for a 4 task job step with a Job ID of 128 and step id of 0 are included below:

    job%J.out
        job128.0.out

    job%4j.out
        job0128.out

    job%j-%2t.out
        job128-00.out, job128-01.out, ...

        Allocate Mode

        When the allocate option is specified (-A, --allocate) srun will not initiate any remote processes after acquiring resources. Instead, srun will spawn a subshell which has access to the acquired resources. Subsequent instances of srun from within this subshell will then run on these resources.

        If the name of a script is specified on the commandline with --allocate, the spawned shell will run the specified script. Resources allocated in this way will only be freed when the subshell terminates.

        Attaching to a running job

        Use of the -a jobid (or --attach) option allows srun to reattach to a running job, receiving stdout and stderr from the job and forwarding signals to the job, just as if the current session of srun had started the job. (stdin, however, cannot be forwarded to the job).

        There are two ways to reattach to a running job. The default method is to attach to the current job read-only. In this case, stdout and stderr are duplicated to the attaching srun, but signals are not forwarded to the remote processes (A single Ctrl-C will detach this read-only srun from the job). If the -j (--join) option is is also specified, srun "joins" the running job, and is able to forward signals and acts for the most part much like the srun process that initiated the job.

        Attaching to running batch jobs is also supported, if the batch job is being managed by SLURM (That is, a script submitted with srun -b). The stdout and stderr from the batch script will then be copied to the attaching srun, and if -j is also specified, signals will be sent to the batch script. This feature provides a good method for determining the status of a running srun within a batch script. For example, consider attaching to a running batch job with jobid 483:
        > srun --join --attach 483
        After pressing Ctrl-C twice within one second, SIGINT is forwarded to the batch job script, and the running srun reports its status:
        attach[483]: interrupt (one more within 1 sec to abort)
        attach[483]: sending Ctrl-C to job
        srun: interrupt (one more within 1 sec to abort)
        srun: task[0-15]: running
        showing that all 16 tasks in the current job step are running.

        Node and CPU selection options do not make sense when specifying --attach, and it is an error to use -n, -c, or -N in attach mode.

ENVIRONMENT VARIABLES

Some srun options may be set via environment variables. These environment variables, along with their corresponding options, are listed below. (Note: commandline options will always override these settings)

SLURM_CPUS_PER_TASK
    -c, --ncpus-per-task=n

SLURM_DEBUG
    -v, --verbose

SLURMD_DEBUG
    -d, --slurmd-debug

SLURM_DISTRIBUTION
    -m, --distribution=(block|cyclic)

SLURM_NNODES
    -N, --nodes=(n|min-max)

SLURM_NPROCS
    -n, --nprocs=n

SLURM_OVERCOMMIT
    -o, --overcommit

SLURM_PARTITION
    -p, --partition=partition

SLURM_STDERRMODE
    -e, --error=mode

SLURM_STDINMODE
    -i, --input=mode

SLURM_STDOUTMODE
    -o, --output=mode

SLURM_WAIT
    -W, --wait=seconds

Additionally, srun will set some environment variables in the environment of the executing tasks on the remote compute nodes. These environment variables are:

SLURM_JOBID
    job id of the executing job.

SLURM_RANK
    the MPI rank of the current process

SLURM_NPROCS
    total number of processes in the current job

SLURM_NODELIST
    list of nodes that the slurm job is executing on.

SIGNALS AND ESCAPE SEQUENCES
Signals sent to the srun command are automatically forwarded to the tasks it is controlling with a few exceptions. The escape sequence <control-c> will report the state of all tasks associated with the srun command. If <control-c> is entered twice within one second, then the associated SIGINT signal will be sent to all tasks. If a third <control-c> is received, the job will be forcefully terminated without waiting for remote tasks to exit. The escape sequence <control-z> is presently ignored. Our intent is for this put the srun command into a mode where various special actions may be invoked.

MPI SUPPORT
On computers with a Quadrics interconnect, srun directly supports the Quadrics version of MPI without modification. Applications build using the Quadrics MPI library will communicate directly over the Quadrics interconnect without any special srun options. Users may also use MPICH on any computer where that is available. The mpirun command may need to be provided with information on its command line identifying the resources to be used. The installer of the MPICH software may configure it to perform these steps automatically. At worst, you must specify two parameters:

-np SLURM_NPROCS
    number of processors to run on

-machinefile <machinefile>
    list of computers on which to execute. This list can be constructed executing the command srun /bin/hostname and writing its standard output to the desired file. Execute mpirun --help for more options.

EXAMPLES
This simple example demonstrates the execution of the command hostname in eight tasks. At least eight processors will be allocated to the job (the same as the task count) on however many nodes are required to satisfy the request. The output of each task will be proceeded with its task number.
> srun -n8 -l hostname This example demonstrates how one might submit a script for later execution (batch mode). The script will be initiated when resources are available and no higher priority job is pending for the same partition. The script will execute on 4 nodes with one task per node implicit. Note that the script executes on one node. For the script to utilize all allocated nodes, it must execute the srun command or an MPI program.
> cat my_script
#!/bin/csh
date
srun -l hostname
> srun -N4 -b my_script This example demonstrates how one executes a simple MPICH job in the event that MPICH has not been configured to automatically set the required parameters (this is the worst cases scenario). We use srun to build a list of machines (nodes) to be used by mpirun in its required format. A sample command line and the script to be executed follow.
> cat my_script #!/bin/csh
srun /bin/hostname >nodes
mpirun -np $SLURM_NPROCS -machinefile nodes /bin/hostname
rm node_list
> srun -N2 -n4 my_script If MPICH is configured to directly use SLURM, the execute line is the much simpler:
> mpirun -np 4 /bin/hostname

BUGS
If the number of processors per node allocated to a job is not evenly divisible by the value of cpus-per-node, tasks may be initiated on nodes lacking a sufficient number of processors for the desired parallelism. For example, if cpus-per-node is three, nprocs is four and the job is allocated three nodes each with four processors. The requisite 12 processors have been allocated, but there is no way for the job to initiate four tasks with each of them having exclusive access to three processors on the same node. The nodes and mincpus options may be helpful in preventing this problem.

SEE ALSO
scancel(1), scontrol(1), squeue(1), slurm.conf(5)