While running a jar in Docker, do you encounter the message “unable to access jarfile”? At Bobcares, with our Docker Hosting Support Service, we can assist you with these issues.

What is meant by “unable to access jarfile” in Docker?

The error message “unable to access jarfile” usually appear when we try to run a Docker container. It means Docker has some (unspecified) issues with that jarfile. In this article, we will see some of the possible reasons of the error and how to fix it.

Case 1

We will use the CMD [ ] command to execute the jar file. With CMD [ ] “exec” format, Docker will try to look at the arguments and give its opinion about their usefulness. For instance, if the Docker cannot handle when the name of the jarfile contained an ENV variable.

Additionally, there is the CMD “shell” format: CMD java -jar jar-runner.jar “some param” “some param”. Due to the fact that Docker passes the arguments to /bin/sh -c, this is known as the shell format. Therefore, it is not attempting to infer what the arguments mean. Sh doesn’t attempt to be intelligent either. And using jar-runner.jar is entirely possible with Java.

Docker’s message might be accurate if jar-runner.jar contained a typo or had been placed in the incorrect location. When Docker makes a bad guess, the shell workaround is helpful.

Case 2

The error message also appears when the volume is mounted, so if our assumption that the jar file is available in the container through that volume is correct, all we need to do is specify the path so that Java can locate it.

CMD ["java", "-jar", "/home/selfbot/jar-runner.jar", "some param", "some param"]

By using a different command to only display the contents of a specific directory, we can determine whether the file is actually accessible. In Portainer, change the command to something like:

ls -la /home/selfbot

Now that we know where the jar file is, we can check to see if it is readable, etc. The output of this command will be immediately exited, but it will still be accessible in the container log.

Case 3

Sometimes the below command can also fix the error.

 ENTRYPOINT ["java","-jar","jar-runner.jar"] CMD ["some param"] 

Case 4

We can also fix it by adding this code to the bottom:

ENTRYPOINT ["java","-jar","repo-connector-1.5.4.jar"] CMD ["-start"]

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Conclusion

To sum up, our Support team went over the “unable to access jarfile” in Docker details.