Cluster Cosmology

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h1. How to run jobs on the euclides nodes

Use slurm to submit jobs to the euclides nodes (node1-8), ssh login access to those nodes will be restricted in the near future.

*Please read through this entire wikipage so everyone can make efficient use of this cluster*

h2. alexandria

*Please do not use alexandria as a compute node* - it's hardware is different from the nodes. It hosts our file server and other services that are important to us. 

You should use alexandria to

- transfer files

- compile your code

- submit jobs to the nodes

If you need to debug, please start an interactive job to one of the nodes using slurm. For instructions see below.

h2. euclides nodes

Job submission to the euclides nodes is handled by the slurm jobmanager (see http://slurm.schedmd.com and https://computing.llnl.gov/linux/slurm/). 

*Important: In order to run jobs, you need to be added to the slurm accounting system - please contact Kerstin*

All slurm commands listed below have very helpful man pages (e.g. man slurm, man squeue, ...). 

If you are already familiar with another jobmanager the following information may be helpful to you http://slurm.schedmd.com/rosetta.pdf‎.

h3. Scheduling of Jobs

At this point there are two queues, called partitions in slurm: 

* *normal* which is the default partition your jobs will be sent to if you do not specify it otherwise. At this point there is a time limit of

two days. Jobs at this point can only run on 1 node.

* *debug* which is meant for debugging, you can only run one job at a time, other jobs submitted will remain in the queue. Time limit is

12 hours.

We have also set up a scheduler that goes beyond the first come first serve - some jobs will be favoured over others depending

on how much you or your group have been using euclides in the past 2 weeks, how long the job has been queued and how much

resources it will consume.

This is serves as a starting point, we may have to adjust parameters once the slurm jobmanager is used. Job scheduling is a complex

issue and we still need to build expertise and gain experience what are the user needs in our groups. Please feel free to speak out if

there is something that can be improved without creating an unfair disadvantage for other users.

You can run interactive jobs on both partitions.

h3. Running an interactive job with slurm

To run an interactive job with slurm in the default partition, use

<pre>

srun -u --pty bash

</pre>

If you want to use tcsh use

<pre>

srun -u --pty tcsh

</pre>

In case you want to open x11 applications, use the --x11=first option, e.g.

<pre>

srun --x11=first -u   --pty  bash

</pre>

In case the 'normal' partition is overcrowded, to use the 'debug' partition, use:

<pre>

srun --account cosmo_debug -p debug -u --pty bash # if you are part of the Cosmology group

srun --account euclid_debug -p debug -u --pty bash  # if you are part of the EuclidDM group

</pre> As soon as a slot is open, slurm will log you in to an interactive session on one of the nodes.

h3. Running a simple once core batch job with slurm using the default partition

* To see what queues are available to you (called partitions in slurm), run:

<pre>

sinfo

</pre>

* To run slurm, create a myjob.slurm containing the following information:

<pre>

#!/bin/bash

#SBATCH --output=slurm.out

#SBATCH --error=slurm.err

#SBATCH --mail-user <put your email address here>

#SBATCH --mail-type=BEGIN

#SBATCH -p normal

/bin/hostname

</pre>

* To submit a batch job use:

<pre>

sbatch myjob.slurm

</pre>

* To see the status of you job, use 

<pre>

squeue

</pre>

* To kill a job use:

<pre>

scancel <jobid>

</pre> the <jobid> you can get from using squeue.

* For some more information on your job use

<pre>

scontrol show job <jobid>

</pre>the <jobid> you can get from using squeue.

h3. Running a simple once core batch job with slurm using the debug partition

Change the partition to debug and add the appropriate account depending if you're part of

the euclid or cosmology group.

<pre>

#!/bin/bash

#SBATCH --output=slurm.out

#SBATCH --error=slurm.err

#SBATCH --mail-user <put your email address here>

#SBATCH --mail-type=BEGIN

#SBATCH -p debug

#SBATCH -account [cosmo_debug/euclid_debug]

/bin/hostname

</pre>

h3. Accessing a node where a job is running or starting additional processes on a node

You can attach and srun command to an already existing job (batch or interactive). This

means you can start an interactive session on a node where a job of yours is running

or start and additional process.

First determine the jobid of the desired job using squeue, then use 

<pre>

srun  --jobid <jobid> [options] <executable> 

</pre>

Or more concrete

<pre>

srun  --jobid <jobid> -u --pty  bash # to start an interactive session

srun  --jobid <jobid> ps -eaFAl  # to start get detailed process information 

</pre>

The processes will only run on cores that have been allocated to you. 

This works for batch as well as interactive jobs. 

*Important: If the original job that was submitted is finished, any process 

attached in this fashion will be killed.*

h3. Batch script for running a multi-core job

mpi is installed on alexandria.

To run a 4 core job for an executable compiled with mpi you can use

<pre>

#!/bin/bash

#SBATCH --output=slurm.out

#SBATCH --error=slurm.err

#SBATCH --mail-user <put your email address here>

#SBATCH --mail-type=BEGIN

#SBATCH -n 4

mpirun <programname>

</pre>

and it will automatically start on the number of nodes specified.

To ensure that the job is being executed on only one node, add

<pre>

#SBATCH -n 4

</pre>

to the job script.

If you would like to run a program that itself starts processes, you can use the

environment variable $SLURM_NPROCS that is automatically defined for slurm

jobs to explicitly pass the number of cores the program can run on.

To check if your job is acutally running on the specified number of cores, you can check

the PSR column of

<pre>

ps -eaFAl

# or ps -eaFAl | egrep "<yourusername>|UID" if you just want to see your jobs

</pre>