Docker executor with systemd

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One of my projects requires systemd to run in the background.
This is perfectly fine for use when installed on the system.
But for testing with gitlab and a docker executor, this is bad.

I can run a docker container with systemd installed.
The entrypoint has to be “/lib/systemd/systemd” (it needs to have PID 1).
Systemd starts and gets to a login shell. I can bypass this and
automatically login to the system.
So “docker run …” gives me a shell in the container.

However, gitlab passes a script to the container upon start.
That would make that script to be PID 1 which does not work with systemd.

Is there another way to get this to work?

I would like to do the following:
(1) “docker run” starts the container, and
(2) “docker exec” runs the script.

Thanks for taking the time to be thorough in your request, it really helps! :blush:*

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Hi @Dennis_1 :wave:

I’ve encountered this same problem before and I couldn’t figure out any way to get systemd to work with GitLab Runner Docker executor. If anyone knows how to do this, please share! :pray:

A potential workaround could be using GitLab Runner’s Shell executor on a machine with Docker installed for any CI jobs that require systemd and docker.

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I believe @nicolamori managed to solve this see this post on stackoverflow, however my attempt to duplicate it initially resulted in a Docker container which, when run on a non-privileged runner, simply returned ERROR: Job failed: exit code 255, however when run on a privileged runner it works perfectly on Debian Bookworm and Ubuntu Jammy however with Debian Bullseye the CI job doesn’t terminate until the GitLab CI timeout is reached — however this might be a molecule issue?

The only part of this potential solution I’ve written myself is the last section of the Dockerfile:

COPY entrypoint.sh /entrypoint.sh
COPY bash.service /etc/systemd/system/bash.service
RUN chown root:root /entrypoint.sh \
    && chmod 755 /entrypoint.sh \
    && chown root:root /etc/systemd/system/bash.service \
    && chmod 644 /etc/systemd/system/bash.service \
    && systemctl enable bash.service
ENTRYPOINT ["/entrypoint.sh"]

Everything else has been copied from the stackoverflow comment linked above.

The only additional Debian package I have installed in the container, for this (I’m doing other things like installing Ansible) is systemd.

Note that for Debian Bullseye systemd is at /lib/systemd/systemd rather than /usr/lib/systemd/systemd where it is found for Debian Bookworm and Ubuntu Jammy.

One potential improvement that the entrypoint.sh script could do with is a check if the container is running in privileged mode with a error message being returned if it is not, see for example the suggestion here however this might not be possible as the check might interfere with the PID assignment?