systemd File Hierarchy Requirements

There are various attempts to standardize the file system hierarchy of Linux systems. In systemd we leave much of the file system layout open to the operating system, but here’s what systemd strictly requires:

The other directories usually found in the root directory (such as /home, /boot, /opt) are irrelevant to systemd. If they are defined they may be mounted from any source and at any time, though it is a good idea to mount them also before is reached.