---
tags:
  - 🚩purpose/ℹ️documentation
  - 🏷️topic/💾software/docker
---
Docker containers are configured with [`ENTRYPOINT`s](https://docs.docker.com/engine/reference/builder/#entrypoint), or commands that are run when the container is initialized. This can be something like the container base image’s  `/sbin/init` or [tinyinit](https://savannah.nongnu.org/projects/tinyinit). Sometimes however, [[NVIDIA in a Non-GNU Environment#Run `ldconfig` after mounting|there is a need to run something before a container’s normal entrypoint]]. Under Docker Compose this is as easy as injecting a command before the container [entrypoint](https://docs.docker.com/compose/compose-file/#entrypoint):
```yaml
    entrypoint: /bin/sh
    command:
      - -c
      - |
        # f.e. cache new libs
        ldconfig

        # anything else you need to do pre-init can go here

        # the original entrypoint/command should go here
        # for example:
        /sbin/init -- /bin/supercoolprogram
```
I was inspired by [@regbo on GitHub](https://github.com/goauthentik/authentik/issues/2364#issuecomment-1341627328) and their use of YAML conventions to make injecting scripts easier.

>[!WARNING] Beware image updates
>If there is an update to the underlying image that changes the entrypoint, you must update your override to point to it, else the container will likely fail to start.