/etc/rc* 未在 Docker 中的 Ubuntu 18.04 上运行。 启动时无法启动 cron

Question

I can't seem to convince the cron (or any other) service to start with my Ubuntu container. I'm sure I'm missing something simple.

I've tried using both update-rc.d and /etc/rc.local but no joy.

In this example Dockerfile I'm also trying to get rsyslog running in order to debug, with the same result- the service does not start.

# syntax = docker/dockerfile:experimental

FROM ubuntu:18.04


RUN apt-get update && apt-get install --reinstall -y \
    rsyslog

# fix for https://stackoverflow.com/questions/56609182/openthread-environment-docker-rsyslogd-imklog-cannot-open-kernel-log-proc-km
RUN sed -i '/imklog/s/^/#/' /etc/rsyslog.conf

# run at startup
RUN update-rc.d rsyslog defaults

# ...really run at startup
RUN echo "service rsyslog start" >> /etc/rc.local

RUN apt-get update && apt-get install -y \
    cron

# run at startup
RUN update-rc.d cron defaults

# ...really run at startup
RUN echo "service cron start" >> /etc/rc.local

ENTRYPOINT ["/bin/bash"]

When I run the container:

root@e392a9404e0f:/# service --status-all
 [ - ]  cron
 [ ? ]  hwclock.sh
 [ - ]  procps
 [ - ]  rsyslog
root@e392a9404e0f:/# service cron start
 * Starting periodic command scheduler cron                                                                             [ OK ] 
root@e392a9404e0f:/# service --status-all
 [ + ]  cron
 [ ? ]  hwclock.sh
 [ - ]  procps
 [ - ]  rsyslog

Answer 1

Add CMD to your Dockerfile:

CMD ["/sbin/init"]

As init, the program is responsible for system initialization. Read more about init here

Answer 2

systemd is not in the ubuntu docker images, by design

This is because its role as PID 1 is effectively replaced by docker's entrypoint

For more, see:

https://stackoverflow.com/a/39169889/1892116

So the correct solution is what I thought was a hack. In my entrypoint.sh I have:

service rsyslog start
service cron start