Docker stop sleeping bash script-CodePudding

I have bash script which runs as docker entrypoint.

This script does some things and then sleeps.

I need to be able to gracefully stop this script when docker stop command is issued. AFAIK docker sends SIGTERM signal to the process 1.

So I created bash script which reacts to SIGTERM.

It works fine without docker, I can launch it, issue kill -TERM <pid> and it gracefully stops the script. Unfortunately it does not work in docker.

Dockerfile:

FROM ubuntu:20.04
WORKDIR /root
COPY test.sh .
CMD ./test.sh

test.sh:

#!/bin/sh
trap 'echo TERM; exit' TERM

sleep 1 &
while wait $!
do
    sleep 1 &
done

How should I modify script or Dockerfile to allow docker stop to work without issues?

Please note that I'm not allowed to pass -it argument to docker run.

CodePudding user response：

The problem comes from the shell form of the CMD instruction: CMD ./test.sh.

In this case the command is executed with a /bin/sh -c shell. So the /bin/sh runs as PID 1 and then forks test.sh, PID 1 is /bin/sh -c ./test.sh. In consequence the SIGTERM signal is sent to the PID 1 and never reaches test.sh.

To change this you have to use the exec form: CMD ["./test.sh"]. In this case, the command will be executed without a shell. So the signal will reach your script.

FROM ubuntu:20.04
WORKDIR /root
COPY test.sh .
CMD ["./test.sh"]

Run and kill.

# run
docker run -d --name trap trap:latest
# send the signal
docker kill --signal=TERM trap
# check if the signal has been received
docker logs trap
# TERM

CodePudding user response：

I suggest you to try with docker kill --signal=SIGTERM <CONTAINER_ID>.

Please let me know if it will work.

CodePudding user response：

Note if your script happens to spawn child process, you may leave behind orphan process upon your docker exit. Try run with --init flag like docker run --init ..., the built-in docker-init executable tini will assumed pid 1 and ensure all child process (such as your sleep example) will be terminated accordingly upon exit.