启动 Rbase docker 容器时如何启动 cron

Question

I'm trying to build a docker container which runs R and cron. What I need is make cron run automatically when I start the container.

My dockerfile is like below:

# Install R version 3.6
FROM r-base:3.6.0

#install crontab
RUN apt-get update && apt-get -y install cron

# also tried CMD /etc/init.d/cron start
CMD cron

Then I built the image and run container in bash. I checked the status of cron:

/etc/init.d/cron status

I got the cron status like below:

[FAIL] cron is not running ... failed!

I was able to start the cron by starting cron mannually:

/etc/init.d/cron start

My question is how I should modify my dockerfile (line CMD ), so that when docker container start, cron start automatically?

Thanks a lot in advance.

Answer 1

CMD /etc/init.d/cron start will start cron in the background so your container will die as soon as it created.

In the second option, add -f

# Install R version 3.6
FROM r-base:3.6.0

#install crontab
RUN apt-get update && apt-get -y install cron

# also tried CMD /etc/init.d/cron start
CMD [ "cron", "-f" ]

So it will keep your container running.

-f
Stay in foreground mode, don't daemonize.

But you will not able to see the cron using /etc/init.d/cron status . use below dokcerfile.

FROM r-base:3.6.0
RUN apt-get update &&  apt-get -y install cron
RUN apt-get install procps -y
CMD ["cron" ,"-f"]

and then run

docker exec -it <your_container_id> bash -c "ps -aux"

You will see that the cron is running.