"Unable to access jarfile" when trying to run a jar with docker

Question

I get Error: Unable to access jarfile jar-runner.jar when trying to run my jar.

Dockerfile:

FROM anapsix/alpine-java
MAINTAINER bramhaag
CMD ["java", "-jar", "jar-runner.jar", "some param", "some param"]

The jar file is located in /home/selfbot/ and I'm running this with Portainer. This is what my Portainer container looks like:

How would I make this work?

Answer 1

With CMD [ ] "exec" format, Docker will try to look at the arguments and give its opinion about their usefulness. "Unable to access jarfile" is a Docker message, and it just means Docker has some (unspecified) issues with a jarfile. I've encountered it when the name of the jarfile contained an ENV variable, for instance. Docker couldn't handle that, apparently.

There's also the CMD "shell" format, CMD java -jar jar-runner.jar "some param" "some param". This is known as the shell format because Docker hands of the arguments to /bin/sh -c. As a result, it's not trying to second-guess what the arguments mean. sh in turn doesn't try to be smart either. And java is entirely capable of using jar-runner.jar.

Mind you, if you've got a typo in jar-runner.jar, or you put it in the wrong location, then Docker's message might be right. The shell workaround is useful when Docker guesses wrong.