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layout: default
navsection: installguide
title: Set up SLURM
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{% comment %}
Copyright (C) The Arvados Authors. All rights reserved.

SPDX-License-Identifier: CC-BY-SA-3.0
{% endcomment %}

On the API server, install SLURM and munge, and generate a munge key.

On Debian-based systems:

<notextile>
<pre><code>~$ <span class="userinput">sudo /usr/bin/apt-get install slurm-llnl munge</span>
~$ <span class="userinput">sudo /usr/sbin/create-munge-key</span>
</code></pre>
</notextile>

On Red Hat-based systems:

<notextile>
<pre><code>~$ <span class="userinput">sudo yum install slurm munge slurm-munge</span>
</code></pre>
</notextile>

Now we need to give SLURM a configuration file.  On Debian-based systems, this is installed at @/etc/slurm-llnl/slurm.conf@.  On Red Hat-based systems, this is installed at @/etc/slurm/slurm.conf@.  Here's an example @slurm.conf@:

<notextile>
<pre>
ControlMachine=uuid_prefix.your.domain
SlurmctldPort=6817
SlurmdPort=6818
AuthType=auth/munge
StateSaveLocation=/tmp
SlurmdSpoolDir=/tmp/slurmd
SwitchType=switch/none
MpiDefault=none
SlurmctldPidFile=/var/run/slurmctld.pid
SlurmdPidFile=/var/run/slurmd.pid
ProctrackType=proctrack/pgid
CacheGroups=0
ReturnToService=2
TaskPlugin=task/affinity
#
# TIMERS
SlurmctldTimeout=300
SlurmdTimeout=300
InactiveLimit=0
MinJobAge=300
KillWait=30
Waittime=0
#
# SCHEDULING
SchedulerType=sched/backfill
SchedulerPort=7321
SelectType=select/linear
FastSchedule=0
#
# LOGGING
SlurmctldDebug=3
#SlurmctldLogFile=
SlurmdDebug=3
#SlurmdLogFile=
JobCompType=jobcomp/none
#JobCompLoc=
JobAcctGatherType=jobacct_gather/none
#
# COMPUTE NODES
NodeName=DEFAULT
PartitionName=DEFAULT MaxTime=INFINITE State=UP

NodeName=compute[0-255]
PartitionName=compute Nodes=compute[0-255] Default=YES Shared=YES
</pre>
</notextile>

h3. SLURM configuration essentials

Whenever you change this file, you will need to update the copy _on every compute node_ as well as the controller node, and then run @sudo scontrol reconfigure@.

*@ControlMachine@* should be a DNS name that resolves to the SLURM controller (dispatch/API server). This must resolve correctly on all SLURM worker nodes as well as the controller itself. In general SLURM is very sensitive about all of the nodes being able to communicate with the controller _and one another_, all using the same DNS names.

*@SelectType=select/linear@* is needed on cloud-based installations that update node sizes dynamically, but it can only schedule one container at a time on each node. On a static or homogeneous cluster, use @SelectType=select/cons_res@ with @SelectTypeParameters=CR_CPU_Memory@ instead to enable node sharing.

*@NodeName=compute[0-255]@* establishes that the hostnames of the worker nodes will be compute0, compute1, etc. through compute255.
* There are several ways to compress sequences of names, like @compute[0-9,80,100-110]@. See the "hostlist" discussion in the @slurm.conf(5)@ and @scontrol(1)@ man pages for more information.
* It is not necessary for all of the nodes listed here to be alive in order for SLURM to work, although you should make sure the DNS entries exist. It is easiest to define lots of hostnames up front, assigning them to real nodes and updating your DNS records as the nodes appear. This minimizes the frequency of @slurm.conf@ updates and use of @scontrol reconfigure@.

Each hostname in @slurm.conf@ must also resolve correctly on all SLURM worker nodes as well as the controller itself. Furthermore, the hostnames used in the configuration file must match the hostnames reported by @hostname@ or @hostname -s@ on the nodes themselves. This applies to the ControlMachine as well as the worker nodes.

For example:
* In @slurm.conf@ on control and worker nodes: @ControlMachine=uuid_prefix.your.domain@
* In @slurm.conf@ on control and worker nodes: @NodeName=compute[0-255]@
* In @/etc/resolv.conf@ on control and worker nodes: @search uuid_prefix.your.domain@
* On the control node: @hostname@ reports @uuid_prefix.your.domain@
* On worker node 123: @hostname@ reports @compute123.uuid_prefix.your.domain@

h3. Automatic hostname assignment

The API server will choose an unused hostname from the set given in @application.yml@, which defaults to @compute[0-255]@.

If it is not feasible to give your compute nodes hostnames like compute0, compute1, etc., you can accommodate other naming schemes with a bit of extra configuration.

If you want Arvados to assign names to your nodes with a different consecutive numeric series like @{worker1-0000, worker1-0001, worker1-0002}@, add an entry to @application.yml@; see @/var/www/arvados-api/current/config/application.default.yml@ for details. Example:
* In @application.yml@: <code>assign_node_hostname: worker1-%<slot_number>04d</code>
* In @slurm.conf@: <code>NodeName=worker1-[0000-0255]</code>

If your worker hostnames are already assigned by other means, and the full set of names is known in advance, have your worker node bootstrapping script (see "Installing a compute node":install-compute-node.html) send its current hostname, rather than expect Arvados to assign one.
* In @application.yml@: <code>assign_node_hostname: false</code>
* In @slurm.conf@: <code>NodeName=alice,bob,clay,darlene</code>

If your worker hostnames are already assigned by other means, but the full set of names is _not_ known in advance, you can use the @slurm.conf@ and @application.yml@ settings in the previous example, but you must also update @slurm.conf@ (both on the controller and on all worker nodes) and run @sudo scontrol reconfigure@ whenever a new node comes online.