Running systemd inside a docker container (arch linux)

I am trying to see if I can run systemd inside a docker container (which is running arch linux in the container).

I start docker with all capabilities, and bind mount in cgroups:

docker run -it --rm --privileged -v /sys/fs/cgroup:/sys/fs/cgroup:ro ..

however, if I try to run the systemd binary:

Trying to run as user instance, but the system has not been booted with systemd.

Trying to find out how to init things correctly to systemd starts.

Here my master pice :D running systemd inside a docker container with ubuntu :D I Got Ubuntu working with systemd inside docker

GitHub Repo for my docker-systemd container

$ docker run -it --cap-add SYS_ADMIN -v /sys/fs/cgroup:/sys/fs/cgroup:ro dockerimages/docker-systemd


Detected virtualization 'docker'.
Detected architecture 'x86-64'.

Welcome to Ubuntu Vivid Vervet (development branch)!

Set hostname to <502ec40509a5>.
[ OK ] Created slice Root Slice.
[ OK ] Created slice System Slice.
Starting Emergency Shell…
[ OK ] Started Emergency Shell.
Startup finished in 5ms.
Welcome to emergency mode! After logging in, type "journalctl -xb" to view
system logs, "systemctl reboot" to reboot, "systemctl default" or ^D to
try again to boot into default mode.
root@502ec40509a5:~# exit

Update 2021

A lot of Patches got Submitted to diffrent Projects like the docker upstream repos by REDHAT. To be More clear my frind David Walsh @ REDHAT did also post a lot about that.

Running SystemD Without additional Privileges requires

/run as a tmpfs. /sys/fs/cgroup read/only. /sys/fs/cgroup/systemd read/write. /etc/machine-id Needs to Contain a Uniqe MachineID SIGRTMIN+3 as stopsignal as sigterm will not work /var/log/journal If it does not exist it will write to memory

docker run -d \ 
    --tmpfs /tmp \
    --tmpfs /run \
    -v /sys/fs/cgroup:/sys/fs/cgroup:ro \
    --stop-signal SIGRTMIN+3 \
    httpd /sbin/init

Note: The Stopsignal flag can be droped when your dockerfile contains STOPSIGNAL SIGRTMIN+3

See the full Post.

Note: Today with Podman this would be even more simple read about it here:

To run systemd in a Docker container, the host system must also run systemd. This means you cannot use Ubuntu < 16.04 as the host.

As of 2018, this now works for me: docker run -it -e container=docker your-image-name /sbin/init

This won't give you a shell, however, so you will need to first enable some systemd service (e.g. sshd) inside the image if that hasn't already been done, to do anything useful.

Found this question while trying to do this in the debian:8 official container. For anyone else trying to do this on the official debian:8 (debian:jessie) container, @Frank-from-DSPEED's answer works with a slight modification as described in an older git hub post:

docker run -d \
    -v /sys/fs/cgroup:/sys/fs/cgroup:ro \
    --cap-add SYS_ADMIN \
    debian:jessie  /sbin/init
docker exec -it <your-new-container-name-or-ID> bash

Then from in the container:

systemctl show-environment

This works perfectly for me and since this is only a development environment, the security issue does not matter to me.

Note: The /sbin/init command gets /sbin/init to be Process 1, which is a key part of making this work.

I was able to work backwards from this:

Docker 1.1 makes this easier as groups (ro) is already provided in containers - I still currently need priv access so it can create PrivateTmp mounts, but otherwise, as long as you specify the cmd to run as the systemd binary - it works nicely.

You can run systemd inside a docker container. The host OS doesn't matter, although you will need to mount the host's /sys/fs/cgroup volume. I got it to work following this guide:

Could you explain why you need systemd?

The systemd man page would be a good place to start. Google also yields several articles about running systemd under docker.