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This article is for both mox.hyak (hyak nextgen) and for ikt.hyak (hyak classic).

(For historical reasons, the title of this page is Mox_scheduler.)

Mox and ikt use a scheduler called slurm.

Below xyz is your hyak group name and abc is your UW netid.

Find out from your group members, whether you should logon to mox or to ikt. Some groups have nodes on both mox and ikt. Some groups have nodes only on ikt or only on mox.

To logon mox:

ssh abc@mox.hyak.uw.edu

To logon ikt:

ssh abc@ikt.hyak.uw.edu

The above command gives you access to the login node of mox or ikt. The login node is only for logging in and submitting jobs. The computational work is  done on a compute node. As shown below, you can get either an interactive compute node or submit a batch job. The build node is a special compute node which can connect to the internet.

To see information about your partition (aka allocations):

sinfo -p xyz

To see the usage of your group's nodes:

squeue -p xyz

To see your jobs:

squeue -u abc

Below mox specific command  shows  the number of nodes etc. of all allocations.

hyakalloc

Interactive Single Node Usage with srun:

The build node can connect to outside mox. It is useful for using git, transferring files to outside mox or getting files from outside mox, installing packages in R or Python etc.

To get an interactive build node for 2 hours:

For mox.hyak:

srun -p build --time=2:00:00 --mem=20G --pty /bin/bash

For ikt.hyak:

srun -p build --time=2:00:00 --mem=10G --pty /bin/bash

(Note: (a) --pty /bin/bash must be the last option in above command.

           (b) If you do not get a build node with above values of --mem, then try smaller values.

           (c) You can connect to the internet from the build node.)



To get an interactive node with 4 cores in your own group for 2 hours on mox:

srun -p xyz -A xyz --nodes=1 --ntasks-per-node=4 --time=2:00:00 --mem=100G --pty /bin/bash

Note that if you are using an interactive node to run a parallel application such as Python multiprocessing, MPI, OpenMP etc. then the number in the --ntasks-per-node option must match the number of processes used by your application. For example for the above srun command:

(a) For Python multiprocessing use code like "p=multiprocessing.Pool(4)".

(b) For MPI use, "mpirun -np 4 myprogram"

(c) For OpenMP use "export omp_num_threads=4"

(d) For GNU parallel use  "-j 4" option


For ikt, use --mem=58G.

On mox and ikt, the -p and -A options are usually the same.

However, when you are using the build node with "-p build", then you do not need to give the -A option.

Also if your group has an interactive node then use the  xyz-int for the -p option. For example:

srun -p stf-int -A stf --time=1:00:00 --mem=10G --pty /bin/bash

Note that an interactive node in your own group cannot connect to outside mox or ikt.

Specifying memory:

           (1) It is important to use the --mem option to specify the required memory. If the memory is not specified then the the SLURM scheduler limits the usage of memory to

                a default value even if more memory is available on the node. Usually the default value is quite low.

           (2) For ikt.hyak regular compute node use, --mem=58G . For ikt.hyak for build node, use --mem=10G.

           (3) If you know that your group has larger memory nodes, then you can use larger values in --mem option.

                The value in --mem option should be smaller than the memory on the node. This is because the operating system also needs some memory

              For 64GB nodes, use --mem=58G   (This is the smallest memory node on ikt.)  

              For 128GB nodes, use ---mem=120G (This is the smallest memory node on mox.)

              For 256GB nodes, use --mem=248G

              For 512GB nodes, use --mem=500G

              For 192GB nodes, use --mem=185G

              For 384GB nodes, use --mem=374G           

              For 768GB nodes, use --mem=752G

              For the knl nodes, use --mem=200G


SLURM environment variables:

Issue below comand at an interactive node prompt to find the list of SLURM environment variables:

export | grep SLURM



Interactive Multiple Node Usage with srun:

If you are setting up an application which uses multiple nodes (e.g. Apache Spark), you will need interactive access to multiple nodes .

To get 2 nodes with 28 cores per node for interactive use:

srun --nodes 2 --ntasks-per-node 28 -p xyz -A xyz  --time=2:00:00 --mem=100G --pty /bin/bash

When the above command runs, then you will have been allocated 2 nodes but will be on one of the two allocated node. The --mem option is for memory per node.

In order to find the names of the nodes that you have been allocated, issue below command:

scontrol show hostnames

Once you know the node names, then you can use them for your work (e.g. Apache Spark, Hadoop etc.)

Below command will tell you about other SLURM environment variables.

export | grep SLURM


Using the checkpoint ckpt queue:

See below link for using the mox and ikt ckpt queue:

Mox_checkpoint


scancel

Use scancel to cancel jobs. For example to cancel a job with job id 1234:

scancel 1234

If your userid is abc then you can cancel all your jobs by using below command:

scancel -u abc

sstat

Use sstat for information (e.g. memory usage) about your currently running jobs.

sstat --format=jobid,MaxVMSize

For details of other format options see https://slurm.schedmd.com/sstat.html

sacct

Use sacct for information (e.g. memory usage) about your jobs which have completed.

sacct --format=jobid,elapsed,MaxVMSize

For details of other format options see https://slurm.schedmd.com/sacct.html

sreport

For historical usage for group xyz for month of March 2018:

sreport cluster UserUtilizationByAccount Start=2018-03-01 End=2018-03-31 Accounts=xyz


Batch usage Single Node:

Submit a batch job from mox login node:

sbatch myscript.slurm

Below is an example slurm script. The --mem option is for memory per node. Replace the last line "myprogram" with the commands to run your program (e.g. load modules, copy input files, run your program, copy output files etc.).

#!/bin/bash

## Job Name

#SBATCH --job-name=myjob

## Allocation Definition

## The account and partition options should be the same except in a few cases (e.g. ckpt queue and genpool queue).

#SBATCH --account=xyz
#SBATCH --partition=xyz

## Resources

## Total number of Nodes

#SBATCH --nodes=1   

## Number of cores per node

#SBATCH --ntasks-per-node=28

## Walltime (3 hours). Do not specify a walltime substantially more than your job needs.

#SBATCH --time=3:00:00

## Memory per node. It is important to specify the memory since the default memory is very small.

## For mox, --mem may be more than 100G depending on the memory of your nodes.

## For ikt, --mem may be 58G or more depending on the memory of your nodes.

## See above section on "Specifying memory" for choices for --mem.

#SBATCH --mem=100G

## Specify the working directory for this job

#SBATCH --chdir=/gscratch/xyz/abc/myjobdir

##turn on e-mail notification

#SBATCH --mail-type=ALL

#SBATCH --mail-user=your_email_address

## export all your environment variables to the batch job session

#SBATCH --export=all


myprogram


Batch usage Multiple Nodes:

If you use multple nodes in one batch job, then your program should know how to use all the nodes. For example, your program should be a MPI program.

Use the same batch file as above batch file for single node except change the number of nodes as shown below.

The value for the --nodes option should be equal to or less than the total number of nodes owned by your group.

The value of the --ntasks-per-node option should be 16 for ikt. It should be 28 for older mox nodes and 40 for newer mox nodes. (Do not increase the values. However, you can decrease them if your progam is running out of memory on a node.)

For ikt:

#SBATCH --nodes=4
#SBATCH --ntasks-per-node=16
For mox:
#SBATCH --nodes=4
#SBATCH --ntasks-per-node=28
# OR

#SBATCH --ntasks-per-node=40



Self-limiting your number of running jobs:

At times you may wish to self-limit the number of your jobs that will be run simultaneously in order to leave nodes in your group's allocation available for immediate use by others in your group.  To achieve this, you can assign one of the "MaxJobs<N>" QOSs to your job, where <N> is the number (1 through 10) of jobs with the same QOS selected that will be run at a time.  NOTE: This is not enabled on the ckpt partition.
For example, adding the following to your script:

#SBATCH --qos=MaxJobs2

...would tell the scheduler to only allow two jobs with the 'MaxJobs2' QOS selected to be run at a time.  Any jobs you start without the 'MaxJobs2' QOS set would not be limited, and jobs with a different MaxJobs<N> QOS set will be limited separately (so, for a example, you could have one set of submitted jobs with the MaxJobs1 QOS selected, and another set with the MoxJobs2 QOS selected. This would result in a total of up to three running jobs at a time; one from the former set, and two from the latter).


Common Slurm Error messages:

Below are some common error messages from slurm. You may see other errors in slurm .out and .err files.

(1) If you use "--mem 120G" and your program uses more memory than 120G then your slurm job will end and you will get below error in the slurm output file. Slurm output files have names like slurm-348658.out.
slurmstepd: error: Exceeded job memory limit


(2) If you use "--time X" and X is greater than the time to the next mox.hyak or ikt.hyak maintenance day then your job will not start and your will get below error:

(ReqNodeNotAvail, UnavailableNodes:n[<node numbers list>]


(3) If you use "-p xyz -A xyz" and you do not belong to the xyz group then you will get below error:

Unable to allocate resources: Invalid account or account/partition combination specified


More details are here:

Hyak mox Overview

https://slurm.schedmd.com/quickstart.html

https://slurm.schedmd.com/documentation.html



===== Below is for Advanced users only ====

Below is about salloc. Do not use salloc unless you have a specific reason.


Interactive Multiple Node Usage with salloc:

If you are setting up an application which uses multiple nodes (e.g. Apache Spark), you will need interactive access to multiple nodes .

To get 2 nodes for interactive use:

salloc -N 2 -p xyz -A xyz  --time=2:00:00 --mem=100G

When the above command runs, then you will have been allocated 2 nodes but will still be on the mox login node.

If you issue a command like below then srun will run the command hostname on each node:

srun hostname

In order to find the names of the nodes that you have been allocated, issue below command:

scontrol show hostnames

Once you know the node names, then you can use them for your work (e.g. Apache Spark, Hadoop etc.)

Below command will tell you about other SLURM environment variables.

export | grep SLURM


srun vs salloc

If no nodes have been allocated then (1) and (2) are equivalent.

(1) srun -p xyz -A xyz --time=4:00:00  --mem=100G --pty /bin/bash

(2) salloc -p xyz -A xyz --time=4:00:00   --mem=100G          This allocates the node.

     srun --pty /bin/bash            This uses the same node.

If nodes have already been allocated by using salloc then srun just uses those nodes.

Alternative to srun is to allocate a node and then ssh to it e.g.

Allocate a node:

salloc -p xyz -A xyz --time=4:00:00 --mem=100G

Find the name of the allocated node:

export | grep LIST

If above command gives a hostname of n1234 then you can ssh to n1234 and use it for your work.

If you you use srun to get an interactive node then when you exit the node, your access to the node also ends.

If you use salloc followed by ssh to get an interactive node then when you exit the node, the node will still be allocated to you. Hence, you can again ssh to the node till the till the time in the salloc command is over.



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