Singularity Summary and Tips

How to create singularity recipe file

Three important sections should be defined in recipe file.

1: BootStrap: in this section you can figure out use which method (library, docker, debootstrap/yum) to get which OS (ubuntu, centos, redhat) with which version (trusty, xenial) from where (singularity hub, docker hub, ubuntu/centos official website) and install which libraries (bash vim less) by default.

  Example 1 
  BootStrap: debootstrap
  OSVersion: xenial
  MirrorURL: http://us.archive.ubuntu.com/ubuntu/
  Include: bash vim less man-db apt-utils tzdata
  ---------
  Example 2
  BootStrap: docker
  From: ubuntu:xenial

2: %environment: in this section, you can figure out the language and location of OS. inaddition, you an export some paths into environment variables inside singularity container.

  %environment
      LC_ALL=C
      LD_LIBRARY_PATH=/usr/local/lib64:/usr/local/lib:/usr/lib64:/usr/lib:/lib64:/lib:/usr/local/cuda/extras/CUPTI/lib64
      TZ='America/New_York'
      export LC_ALL LD_LIBRARY_PATH TZ   

3: %post: in this section, you can figure out all customized script that be used to install the specific libraries, software and packages.

  %post	
      #Get 3DSlicer
      wget -P /home/software/3DSlicer https://download.slicer.org/bitstream/1023242
      tar -xvf /home/software/3DSlicer/1023242 -C /home/software/3DSlicer		
      #For 3DSlicer
      apt-get install -y libfontconfig1 \
                         libxrender1 \
                         libgl1-mesa-dev \
                         libglu1-mesa \
                         libglu1-mesa-dev \
                         libxtst6 \
                         libegl1-mesa-dev

4: Example

(1)The singularity recipe file for 3DSlicer: https://github.com/lxwgcool/singularity/blob/master/singularity_3DSlicer.recipe
(2)The singularity recipe file for tensorflow with ubuntu xenial, python 3.6.7 and cuda 9.0: https://github.com/lxwgcool/singularity/blob/master/Singularity.tensorflow-gpu-1.12.0

How to create singularity container

1: There are two types of container, including "image" and "sandbox".

2: Any singularity container should be created by using "sudo".

Now, we use the recipe file of 3D Slicer as an example: https://github.com/lxwgcool/singularity/blob/master/singularity_3DSlicer.recipe

Image

sudo singularity build ./3DSlicer.ssb ../singularity_3DSlicer.recipe

Advantage
1: Singularity image container is a binary file.
2: The size of image container is small.
 
Disadvantage
1: Hard to be expanded (size is fixed).
2: You are not allowed to install new packages and libraries once the image been created.

Sandbox

sudo singularity build --sandbox ./3DSlicer.ssb ../singularity_3DSlicer.recipe

Advantage
1: It is very easy to be expanded (no size limitation). 
2: You can install any additional packages and libraries after the container been created.
3: Sandbox is very easy to be converted to image by using the command line below:
   sudo singularity build 3DSlicer.sif 3DSlicer.ssb/

Disadvantage
1: Singularity sandbox container is a folder.
2: The size of sandbox container is around 3 times larger than image container.

Recommendation: since the storage is not a big issue for modern computer, sandbox is good choice to used when build singularity container.