Revision as of 15:42, 12 May 2017

Singularity allows complex software to be run on the cluster, that would otherwise be difficult or impossible to install. Using singularity, you can generate a single "image" file in which you install all your software, and then you can copy that single image file to the cluster and run it there. Additionally, singularity allows more directly comparisons of running software between different clusters, because you can use the exact same versions of software that may not be installed on the different clusters.

This guide will help you create your own singularity images.

Requirements:

• Your computer with macOS, Windows, or a GNU/Linux operating system.
• VirtualBox to create a virtual machine in which we will install singularity.
• Vagrant (version 1.9 or later) to greatly simplify administration of our virtual machine.
• At least 40 GB of disk space.

Getting started

To be able to create and edit a singularity image, you must have root administrator access on a machine. Therefore you cannot manage singularity containers directly on the cluster; you must install your own copy of singularity on your computer. Singularity uses the Linux kernel to run the container, therefore you need to use a GNU/Linux machine for which we will use a virtual machine. For best results, it also helps to use a Linux distribution similar to the environment in which we will finally run our singularity image. As our cluster uses RHEL 6.7, we will create our singularity image using CentOS which, for our purposes, is functionally identical to RHEL.

If you are using macOS, you can install singularity via homebrew as explained on the singularity page [1] but which we will repeat here for completeness:

# Only run these commands if you are using macOS!

# Install Brew if you do not have it installed already
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

# The next commands will install Vagrant and the necessary bits
brew cask install virtualbox
brew cask install vagrant
brew cask install vagrant-manager

If you are using GNU/Linux, you can install virtualbox and vagrant through your package manager. You may need to log out and log in to your system again for your user account to be recognized as being in the vboxusers group.

Windows users can install virtualbox and vagrant directly from the main websites.

Now that we have the necessary tools, we can create our CentOS virtual machine in which we will install singularity:

# Create a working directory for the Vagrant configuration and
# generate a template Vagrantfile for "centos/7"
mkdir vm-singularity
cd vm-singularity
vagrant init centos/7
vagrant box add --provider virtualbox centos/7  # If this fails, you might need to upgrade vagrant

# Build and start the Vagrant hosted VM
vagrant up --provider virtualbox

# Run the necessary commands within the VM to install Singularity
vagrant ssh -c /bin/sh <<EOF
    sudo yum update
    sudo yum -y install @'development tools' emacs-nox
    git clone https://github.com/singularityware/singularity.git
    cd singularity
    ./autogen.sh
    ./configure --prefix=  # System root to avoid changing sudo secure_path
    make
    sudo make install
EOF

# Singularity is installed in your Vagrant CentOS VM! Now you can
# use Singularity as you would normally by logging into the VM
# directly
vagrant ssh

Creating your singularity image

When you log in with vagrant ssh above, your shell prompt should look similar to:

[vagrant@localhost ~]$

We are inside our CentOS virtual machine.

To create the raw image file use the create command.

sudo singularity create --size 4096 centos7-container.img

We now need to install our software inside the image file by writing a "definition" file. You might be able to use one of several community contributed definition files are in the main singularity repository: singularity/examples/contrib The singularity user documentation also has more detail, but for now we will look at a small example here.

As an example here, we will install R with the rstan package. Create the following centos7-container.def file using your favorite command-line text editor:

 1 # -*- mode: rpm-spec -*-
 2 
 3 # Contents of file "centos7-container.def"
 4 
 5 BootStrap: yum
 6 OSVersion: 7
 7 MirrorURL: http://mirror.centos.org/centos-%{OSVERSION}/%{OSVERSION}/os/$basearch/
 8 Include: yum
 9 
10 # The default command to run once our image is finished.
11 %runscript
12     Rscript $@
13     
14 # Installing the software in our image.
15 %post
16     yum -y install epel-release
17     yum -y install R
18     Rscript -e 'if (! require(rstan)) install.packages("rstan", repo="http://cran.rstudio.com/")'
19 
20 # Command
21 %test
22     Rscript -e 'library(rstan)'

Now we run the %post software installation section with the singularity bootstrap command:

sudo singularity bootstrap centos7-container.{img,def}

The first time singularity runs the bootstrap process, you will see it installing some extra packages before it does anything in your %post steps. It is setting up a minimal operating system inside the image.