How to run a container that crashes on startup

one of the most frustrating things about running with containers is when a container fails immediately on startup.

This can happen for a number of reasons, and not all of them record errors in logfiles to help diagnose them.

However, there’s a fairly easy way to get around this.

Start the container with the “interactive” option and override the “entrypoint” option to execute “/bin/sh”. This will do two things.

  1. Instead or running the normal container startup, it will start the container executing the command shell
  2. The “interactive” option holds the container open. Without it, the command shell sees an immediate end-of-file and shuts down the container.

At this point, you can then use the docker/podman “exec” command to dial in to the container like so:

docker exec my_container /bin/sh

At that point, you can inspect files, run utilities, and do whatever is necessary to diagnose/repair the image.

An additional help is also available once you have a tame container running. You can use the docker/podman “cp” command to copy files into and out of the container. Many containers have minimal OS images and have neither an installed text editor nor a package installer to install a text editor. So you can pull a faulty file out of a container, fix it, and push it back. The changes will persist as long as you restart the container and don’t start a new instance from the original image.

Author: Tim

Evil Genius specializing in OS's, special hardware and other digital esoterica with a bent for Java.