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layout: default
navsection: installguide
title: Singularity container runtime
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Copyright (C) The Arvados Authors. All rights reserved.

SPDX-License-Identifier: CC-BY-SA-3.0
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Arvados can be configured to use "Singularity":https://sylabs.io/singularity/ instead of Docker to execute containers on cloud nodes or a SLURM/LSF cluster. Singularity may be preferable due to its simpler installation and lack of long-running daemon process and special system users/groups.

Please note:
* *Singularity support is currently considered experimental.*
* Even when using the singularity runtime, users' container images are expected to be saved in Docker format using @arv keep docker@. Arvados converts the Docker image to Singularity format (@.sif@) at runtime as needed. Specifying a @.sif@ file as an image when submitting a container request is not yet supported.
* Singularity does not limit the amount of memory available in a container. Each container will have access to all memory on the host where it runs, unless memory use is restricted by SLURM/LSF.
* Programs running in containers may behave differently due to differences between Singularity and Docker.
** The root (image) filesystem is read-only in a Singularity container. Programs that attempt to write outside a designated output or temporary directory are likely to fail.
** The Docker ENTRYPOINT instruction is ignored.
* Arvados is currently tested with Singularity version 3.5.2.

To use singularity, first make sure "Singularity is installed":https://sylabs.io/guides/3.5/user-guide/quick_start.html on your cloud worker image or SLURM/LSF compute nodes as applicable. Note @squashfs-tools@ is required.

<notextile>
<pre><code>$ <span class="userinput">singularity version</span>
3.5.2
$ <span class="userinput">mksquashfs -version</span>
mksquashfs version 4.3-git (2014/06/09)
[...]
</code></pre>
</notextile>

Then update @Containers.RuntimeEngine@ in your cluster configuration:

<notextile>
<pre><code>      # Container runtime: "docker" (default) or "singularity" (experimental)
      RuntimeEngine: singularity
</code></pre>
</notextile>

Restart your dispatcher (@crunch-dispatch-slurm@, @arvados-dispatch-cloud@, or @arvados-dispatch-lsf@) after updating your configuration file.