Monthly Archives: October 2020

Centos, Docker, Linux

Running systemd inside a Centos 8 Docker container

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Support for systemd in Docker has improved a lot since this 2016 article, but it’s still not obvious quite how to make it work. Why would you want this? Mostly for testing full-server deploys (for example we test ansible deployments against various docker containers to ensure there are no bugs).

Here’s a systemd-based centos 8 Dockerfile that also includes an ssh server:

FROM centos:8

# Set up base packages that are expected
RUN dnf -y install openssh-server crontabs NetworkManager firewalld selinux-policy

RUN systemctl mask dev-mqueue.mount dev-hugepages.mount \
     systemd-remount-fs.service sys-kernel-config.mount \
     sys-kernel-debug.mount sys-fs-fuse-connections.mount \
     graphical.target systemd-logind.service \
     NetworkManager.service systemd-hostnamed.service

STOPSIGNAL SIGRTMIN+3

# SSHd setup
EXPOSE 22
COPY docker.pub /root/.ssh/authorized_keys
RUN chmod 600 /etc/ssh/ssh_host* /root/.ssh/authorized_keys

CMD ["/sbin/init"]

You can then launch this like:

docker run -v /sys/fs/cgroup:/sys/fs/cgroup:ro --tmpfs /run container-name

For the latest centos 7 you can use the following Dockerfile:

FROM centos:7

RUN yum -y install openssh-server NetworkManager firewalld && \
    systemctl disable NetworkManager && systemctl enable sshd

EXPOSE 22
COPY docker.pub /root/.ssh/authorized_keys
RUN chmod 600 /etc/ssh/ssh_host* /root/.ssh/authorized_keys

STOPSIGNAL SIGRTMIN+3

CMD ["/sbin/init"]