Docker Tip #91: Exec into a Container as Root without Sudo or a Password
This is handy when you configured your Dockerfile to run as a non-root user but you need to temporarily debug or test something out.
Prefer video? Here’s a recorded version of this tip on YouTube that shows a demo of what’s written below and more.
It’s way easier than you might expect and it doesn’t require using sudo or
knowing / setting a root password! You can run your project however you see
fit, such as with Docker Compose or straight up Docker. Then exec into your
container as root even if you have USER someone defined in your Dockerfile:
# Here's how to do it with Docker Compose:
docker-compose exec -u root [SERVICE] bash
# Here's how to do it with Docker:
docker container exec -it -u root [CONTAINER] bash
This should work on most Linux based images. Technically using -u 0 works too
because on Linux systems the 0 user id is often associated to the root
user. In practice I tend to use root instead of 0 since it hasn’t failed
yet on any Debian based Docker image and I’m only doing this in development for
1 off debugging sessions.
Now you can install system packages or mess with root files to troubleshoot whatever you’re working on without having to resort to modifying your Dockerfile and rebuilding your image for a temporary debug session.