baseimage-docker

When you run Ubuntu inside a Docker container, things break in subtle ways. Ubuntu was built for real machines or virtual servers, not containers. Its normal startup system expects hardware that is not there, and as a result containers accumulate stuck processes over time, logging stops working properly, and shutting down the container can corrupt files rather than close them cleanly. Baseimage-docker is a pre-built Docker image that fixes all of these problems before you write a single line of code.

The image is built on Ubuntu 24.04 and weighs about 8.3 MB of RAM at runtime. It adds a custom startup program called my_init that correctly handles the Unix process lifecycle inside a container, meaning it adopts any orphaned child processes and cleans them up properly. It also replaces Ubuntu's default service manager with runit, a lightweight tool that can supervise multiple services and automatically restart them if they crash. Together these two pieces let you run more than one background program inside a single container without fighting the Docker model.

Other additions include a syslog daemon so that the kernel and system tools can log messages normally, a cron scheduler for scheduled tasks, log rotation, and an optional SSH server (off by default) for logging into a running container to inspect what is happening. There is also a small utility called setuser that lets you run a command as a specific system user without elevated privileges.

The practical benefit is that you can use baseimage-docker as the FROM line in your own Dockerfile instead of the stock Ubuntu image, and all of the corner-case configuration work is already done. You can focus on installing your application rather than patching the operating system to behave correctly in a container. The project documentation walks through adding your own services, passing environment variables in, enabling SSH, and building the image yourself if you need custom modifications.

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