How to run command on stopped Docker container?

Question

I have a Wordpress container which used to work before. Due to the changes on the linked container, the Wordpress container couldn't be started anymore now (the EntryPoint code has error)

Since the Wordpress container contains some configurations which are not stored in the host filesystem, I shouldn't redoing docker run for now. Instead, I wish to bash into the stopped container, check all changed files, and back up those files first.

Is there a way to execute bash on a stopped container? How to do so?

Answer 1

More natural way would be to use the docker diff to inspect changes to the container's filesystem. - will only show the names of the changed files.

If you are lucky to use a mature container and the changes were made on the volumes, you could start a new container with --volumes-from <stopped container>.

Alternatively you could start the stopped container and then do exec to get into it.

Third option would be to commit stopped container as an image and start a new one from it.

Answer 2

docker run -v /mydata --name mydata ubuntu /bin/false

then ...

docker exec mydata touch /mydata/foo # doesn't work if not running :-(

A good solution is to run a throwaway container every time you want to attach to the data container. In this case the data container itself could be entirely empty, as the temporary container would have the OS tools.

$ docker run --rm --volumes-from mydata -it ubuntu bash
root@645045d3cc87:/# ls /mydata
root@645045d3cc87:/# touch /mydata/foo
root@645045d3cc87:/# exit
exit