Creating Singularity container

For some project I had to create a Singularity container (because of the environment where it needs to run). Singularity is a container technology used by scientists. It turned out that it is very simple. Although there is not recent enough Singularity package in the normal Fedora repos, they have nice guide on how to build your own packages and that worked for me on a first try. First "Singularity" build file (similar to "Dockerfile" file) - I have based it on a recent Fedora docker image:

$ cat Singularity 
Bootstrap: docker
From: fedora:latest

%help
    This is a container for ... project
    See https://gitlab.com/...
    Email ...

%labels
    Homepage https://gitlab.com/...
    Author ...
    Maintainer ...
    Version 0.1

%files
    /home/where/is/your/project /projectX

%post
    dnf -y install python2-biopython python2-numpy python2-tabulate python2-scikit-learn pymol mono-core python2-unittest2 python2-svgwrite python2-requests
    chown -R 1000:1000 /projectX   # probably not important

%test
    cd /projectX
    python -m unittest discover

%environment
    export LC_ALL=C

%runscript
    exec /projectX/worker.sh

Majority of above is not needed: e.g. "%help" have completely free form, keys in "%labels" does not seem to be codified, "%test" which is ran as a last step of a build process is also optional. To build it:

$ sudo singularity build --writable projectXy.simg Singularity   # *.simg is a native format of singularity-2.4.6
$ sudo singularity build --writable projectX.img projectX.simg   # where the project is supposed to run, there is 2.3.2 which needs older *.img, so convert *.simg into it

Mine original idea was to have the project in writable container (so the option "--writable" above), but that would require me to run it as root again (or I'm missing something), so I have ended up with the solution of running the container in read-only mode and mounting mine project into it to have a read-write-able directory where I can generate the data:

$ echo "cd /projectX; ./worker.sh" \
      | singularity exec --bind projectX/:/projectX projectX.img bash

So far it looks like it just works.