It’s a common scenario: one of your Docker containers is running, and you need to access its filesystem. Perhaps something has gone wrong and you want to troubleshoot by taking a look at logs, or perhaps there’s a config file that you want to query.

The attach command will allow you to see the standard input, output and error streams of a running container, but what if you’re looking for something that isn’t captured by these streams?

docker attach <options> <container>

Breaking in

Individual Docker containers are princiaplly used to run a single process, or set of processes, but can run as many processes as desired. You can start a new process in a container even whilst it’s running using the exec command.

With this in mind, to gain console access to a running container you simply need to use the exec command to start a new instance of the bash process on the container of interest, providing the -it arguments as follows:

docker exec -it <container> bash

Explaining the options provided to the exec command:

• -i, –interactive: Keep STDIN open even if not attached
• -t, –tty: Allocate a pseudo-TTY

When done, simply type exit and the bash process will be stopped. Barring any modifications you made to the container whilst inside the bash process, it will be as if you were never there.