Singularity

Software name: 
Singularity
Policy 

Singularity is a is a free, cross-platform and open-source computer program that performs operating-system-level virtualization also known as containerization. It is freely available to users at HPC2N.

General 

Singularity is a container system for Linux HPC that lets you define your own environment and makes your work portable and reproducible on any system that supports it. A container is a lightweight, stand-alone, executable package of a piece of software that includes everything needed to run it: code, runtime, system tools, system libraries, settings.

Description 

Singularity enables you to run applications under a different Linux environment than the one you are currently using. This could solve the problem with working with proprietary licensed Linux software that only has support for another Linux distribution.

Other typical examples when to use singularity are:

  • Reproducibility of software contained in a single file that can be used any many HPC centers!
  • Software development performed on RHEL7 (or any Linux distribution that is different from the one in use on HPC2N clusters)
  • Working with proprietary licensed Linux software that doesn't have support for the Linux distribution used on the HPC2N clusters
  • Need the flexibility to work with software immediately on other HPC hardware that runs with Singularity
  • You want to run software quickly because the software versions are rapidly evolving
  • Software metadata files are unmanageable (e.g., installing software with Python, R, conda) – a Singularity container allows for the use of a single compressed image file.

But it is also important to know when singularity is not the best option. For instance:

  • When performance is important. Singularity generally does not slow down your code but the images are usually not optimized for the HPC2N clusters.
Availability 

On HPC2N we have Singularity available as a module.

Usage at HPC2N 

This section will describe how to use Singularity at HPC2N, and how it might differ from how it is used at other sites. The official Singularity documentation can be found at https://sylabs.io/docs/.

Note that this documentation is meant for Singularity 3.x!

Simple usage

To use Singularity, you first need to load the singularity module. This is done with the "module load" command.

This very simple example shows how to run the newer version bash using singularity. It involves loading the latest version of the singularity module, download the bash image once, and then run bash from the image. It is a trivial example and not especially useful but works as an example.

# Load Singularity module
module load singularity
# Download image (once)
singularity pull docker://bash
# Run the image
singularity exec bash_latest.sif bash
# Alternative way that works for this image
./bash_latest.sif

More detailed examples and information on creating an image on this page and running on this page.

Specifics of the HPC2N setup

When running a Singularity image at HPC2N, everything below the following directories from the host environment will be available in the running image: 

  • $HOME
  • /pfs
  • /afs
  • /scratch
  • /tmp

As usual, when running batch jobs, data will have to be placed in the directory tree of a storage project (recommended) or in your $HOME directory tree.

The current configuration have not limited the paths where containers can be stored. Both bind control and fusemount are enabled.  

Comparison, Singularity and Docker

Singularity and Docker provides similar functionality, but there are some important differences in the way they work.

  Docker Singularity
Runs docker containers X X
Edits docker containers X X
Interacts with host devices (like GPUs) X X
Interacts with host filesystems X X
Runs without sudo   X
Runs as host user   X
Can become root in container X X (using fakeroot, not allowed at HPC2N)
Control network interfaces X X (using fakeroot, not allowed at HPC2N)
Configurable capabilities for enhanced security   X

Containers were created to isolate applications from the host environment. This means that all necessary dependencies are packaged into the application itself, allowing the application to run anywhere containers are supported. With container technology, administrators are no longer bogged down supporting every tool and library under the sun, and developers have complete control over the environment their tools ship with. You can find more information about containers on this page

Updated: 2021-07-20, 15:13