Docker return codes from background commands

Question

I'm not getting the return code I expect, when executing a script inside a Docker container with a background task run in it.

This example docker file highlights the problem:

FROM ubuntu:latest
MAINTAINER Jakob H. Thomsen (jakob@gedefar.dk)

RUN echo "#!/bin/bash\nset -e\n\nls / &\nexit 1" > /start_script.sh
RUN chmod +x /start_script.sh 

It creates the following file /start_script.sh inside the container:

#!/bin/bash
set -e

ls / &
exit 1

So running docker build -t jakob/test . and docker run jakob/test cat /start_script.sh you would expect the return code to be 1, because of the exit 1. It is not, it is 0 and it is somehow because of the ls / & (if you remove that command you get the expected return code of 1).

So my question is why ls / & overrides the return code of the exit 1 command? I tried making exit 1 to run in the background, but it doesn't change the return code...

As I'm using the setup to run Ruby specs, I'm really dependent upon the return code of the last command, so is there something I can do to make Docker return the return code of the last command?

Thanks and I hope you can help, as it has taking me a loong time to pinpoint the exact issue of these 'wrong' return codes.

Answer 1

Turned out that the issue is fixed in the newest version of Docker: https://github.com/dotcloud/docker/issues/3775