Is the container booted when we run the container?

[Heng-Zhou]

Here I use "run" in an informal way which represents two cases.

First, when we run commands in %post section during building, has the base OS booted, i.e., the running environment of commands in %post are like in the command line of the base OS after it is booted normally (not in a container)?

Second, when we shell into the container, has the base OS completed booting before showing the Singularity> prompt? Thank you.

[dtrudg]

There is generally no concept of 'booting' a Singularity container. A container shares the kernel of the host system, so there is no low level boot up of drivers etc.

A container does not usually have an init system (generally systemd), nor does it run the various services an OS will when booted on a physical or virtual machine.

When you run commands in %post, the only environment is whatever has been setup by earlier commands, or the base image in your From: line.

When you shell into a container, only the shell process is started inside the container. Generally nothing else is 'booted'.