A documented example of a Singularity container recipe.

singularity.def

Bootstrap: docker
From: ubuntu
# Stage: build

# Setup during build process.
# NOTE: According to docs, this SHOULD NOT be used to
# copy files into the container, use '%files' section instead.
%setup
    touch /file1
    touch ${SINGULARITY_ROOTFS}/file2

# Provides a safer way of copying content to the container.
# NOTE: This is the recommended way of doing so. Better than using
# '%setup' section for the matter. 
%files
    /file1
    /file1 /opt

# Container RUNTIME setup of environment.
# NOTE: These variables are not made available during BUILD
# time, for define them as well in the '%post' section.
%environment
    export LISTEN_PORT=12345
    export LC_ALL=C

# Tool downloading and installations, write configurations, create directories, etc.
# NOTE: Should be used to setup BUILD time environment variables.
%post
    apt-get update && apt-get install -y netcat
    NOW=`date`
    echo "export NOW=\"${NOW}\"" >> $SINGULARITY_ENVIRONMENT

# Called upon container 'singularity run' command.
# NOTE: The content of this section is written in a file inside the container, so
# that it can be run once the aforementioned command is issued.
%runscript
    echo "Container was created $NOW"
    echo "Arguments received: $*"
    exec echo "$@"

# Called upon container's 'singularity instance start' command.
# NOTE: The content of this section is written in a file inside the container, so
# that it can be run once the aforementioned command is issued.
%startscript
    nc -lp $LISTEN_PORT

# Runs at the very end of the BUILD process and can be used to validate the container.
%test
    grep -q NAME=\"Ubuntu\" /etc/os-release
    if [ $? -eq 0 ]; then
        echo "Container base is Ubuntu as expected."
    else
        echo "Container base is not Ubuntu."
    fi

# Adds metadata to the container inside '/.singularity.d/labels.json'.
%labels
    Author [email protected]
    Version v0.0.1

# Adds metadata into the container that can be accessed through 
# 'singularity run-help' command.
%help
    This is a demo container used to illustrate a def file that uses all
    supported sections.