Running systemd in docker container causes host crash

Question

I'm trying to create a systemd based docker container, but when I try running the built container my system crashes. I think running init in the container might be causing the conflict, and is somehow conflicting with systemd on my host.

When I try to run the docker container I am logged out of my account and briefly see what looks like my system going through a boot process. My host is running Arch Linux, with linux 4.20.7.

It is only when I attempt to "boot" the container by running systemd via /sbin/init, that the problem occurs.

docker run -it \
   --volume=/sys/fs/cgroup:/sys/fs/cgroup:rw \
   --privileged 66304e3bc48

---

Dockerfile (adapted from solita/ubuntu-systemd):

FROM ubuntu:18.04

# Don't start any optional services.
RUN find /etc/systemd/system \
    /lib/systemd/system \
    -path '*.wants/*' \
    -not -name '*journald*' \
    -not -name '*systemd-tmpfiles*' \
    -not -name '*systemd-user-sessions*' \
    -exec rm \{} \;

RUN apt-get update && \
    apt-get install --yes \
    python sudo bash ca-certificates dbus systemd && \
    apt-get clean && \
    rm -rf /var/lib/apt/lists/*

RUN systemctl set-default multi-user.target
RUN systemctl mask dev-hugepages.mount sys-fs-fuse-connections.mount

STOPSIGNAL SIGRTMIN+3

# Workaround for docker/docker#27202, technique based on comments from docker/docker#9212
CMD ["/bin/bash", "-c", "exec /sbin/init --log-target=journal 3>&1"]

I would expect the container to just boot up running systemd, and I'm not your what I might be doing wrong.

Answer 1

I ended up using the paulfantom/ubuntu-molecule Docker image.

Currently it looks like they're just installing systemd, setting some environment variables, and using the systemd binary directly as the entry point. It seems to work without the issues I mentioned in the original post.

Dockerfile

FROM ubuntu:18.04

ENV container docker
ENV LC_ALL C
ENV DEBIAN_FRONTEND noninteractive

RUN sed -i 's/# deb/deb/g' /etc/apt/sources.list

# hadolint ignore=DL3008
RUN apt-get update \
    && apt-get install -y --no-install-recommends systemd python sudo bash iproute2 net-tools \
    && apt-get clean \
    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*

# hadolint ignore=SC2010,SC2086
RUN cd /lib/systemd/system/sysinit.target.wants/ \
    && ls | grep -v systemd-tmpfiles-setup | xargs rm -f $1

RUN rm -f /lib/systemd/system/multi-user.target.wants/* \
    /etc/systemd/system/*.wants/* \
    /lib/systemd/system/local-fs.target.wants/* \
    /lib/systemd/system/sockets.target.wants/*udev* \
    /lib/systemd/system/sockets.target.wants/*initctl* \
    /lib/systemd/system/basic.target.wants/* \
    /lib/systemd/system/anaconda.target.wants/* \
    /lib/systemd/system/plymouth* \
    /lib/systemd/system/systemd-update-utmp*

RUN systemctl set-default multi-user.target
ENV init /lib/systemd/systemd
VOLUME [ "/sys/fs/cgroup" ]

ENTRYPOINT ["/lib/systemd/systemd"]