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====== Using SLURM ======
===== What is SLURM? =====
SLURM is an open-source resource manager designed for Linux clusters of all sizes. It provides three key functions. First it allocates exclusive and/or non-exclusive access to resources (computer nodes) to users for some duration of time so they can perform work. Second, it provides a framework for starting, executing, and monitoring work (typically a parallel job) on a set of allocated nodes. Finally, it arbitrates contention for resources by managing a queue of pending work.

{{:images:arch.gif|}}

As depicted in Figure 1, SLURM consists of a slurmd daemon running on each compute node and a central slurmctld daemon running on a management node (with optional fail-over twin). The slurmd daemons provide fault-tolerant hierarchical communications. The user commands include: sacct, salloc, sattach, sbatch, sbcast, scancel, scontrol, sinfo, smap, squeue, srun, strigger and sview. All of the commands can run anywhere in the cluster.



===== Viewing Status of Runs =====

  $ sinfo
  PARTITION AVAIL  TIMELIMIT  NODES  STATE NODELIST
  debug*       up   infinite      2   idle carnot,diesel

sinfo shows the current status of the cluster. It displays the availability, timelimits being enforced, number of nodes, and which nodes are available. The STATE of a node can also be allocated, completing, down, draining, unknown. If a node is marked with an '*', the node is not responding to the controller.

  $squeue
  JOBID PARTITION     NAME     USER  ST       TIME  NODES NODELIST(REASON)
  37     debug    myprogram    james   R       0:04      1 carnot

squeue shows jobs currently in the queue. The State can be one of:
  * R - Running
  * S - Suspended
  * PD - Pending
  * F - Failed
  * CG - Completing
  * TO - Timeout
  * CA - Canceled

  $ sacct
         JobID    JobName  Partition    Account  AllocCPUS      State ExitCode 
  ------------ ---------- ---------- ---------- ---------- ---------- -------- 
  37                sleep      debug                     8  COMPLETED      0:0 

sacct shows jobs that you have run in the past, how much resources they used and their state.

===== Starting a Job with srun =====

  $ srun -n4 --time=0:30 -o myjob.out ./myprogram

===== Starting a Job with sbatch =====
Setting up all of your options everytime you use srun can be repetitive. Use a batch file and submit that instead!

Example file 'mybatch':
  #!/bin/sh
  #SBATCH -n 4
  #SBATCH --time=0:60
  #SBATCH --output=mybatch.out
  srun ./my_program

  $ sbatch mybatch
  Submitted batch job 47


===== Stopping or Canceling Jobs =====


  $ squeue
  JOBID PARTITION     NAME     USER  ST       TIME  NODES NODELIST(REASON)
  37     debug    myprogram    james   R       0:04      1 carnot
  
  $ scancel 37
  
Cancel a job with scancel, then the JobID of the program you want to cancel. You can view the jobID with squeue.

===== More information =====
[[https://computing.llnl.gov/linux/slurm/quickstart.html|Slurm Quickstart]]