Which run level is assigned for custom configurations?

Run level 4 is typically designated for custom configurations in many Linux distributions. This designation allows sysadmins or users to configure the system to suit specific needs without impacting the default behavior of other run levels, which have predefined purposes.

In contrast, run levels 0 through 3 and 5 have established roles: run level 0 is for system halt, run level 1 is for single-user mode (maintenance), run level 2 allows multi-user mode with no networking, run level 3 is multi-user mode with networking but no graphical interface, and run level 5 typically includes a graphical user interface (GUI).

Since run level 4 is not commonly used by default configurations in many distributions, it provides the flexibility for custom scripts and services tailored to specific operational requirements. This makes it an ideal choice for users looking to experiment with or implement unique setups without conflicting with standard configurations that other run levels enforce.