Which SysV init configuration file is commonly used to set the default run level?

The /etc/inittab file is a plain text file that contains information about the initialization process of the system. It defines the default run level, the available run levels, and the actions to be taken when entering or leaving a run level. The default run level is the mode of operation that the system starts up into, and it determines which services and processes are running. The default run level is specified by a line similar to the following in the /etc/inittab file:

id:5:initdefault:

The number after the first colon indicates the default run level, which can range from 0 to 6. The meaning of each run level is:

0 — Halt

1 — Single-user text mode

2 — Not used (user-definable)

3 — Full multi-user text mode

4 — Not used (user-definable)

5 — Full multi-user graphical mode (with an X-based login screen)

6 — Reboot

To change the default run level, edit the /etc/inittab file as root and change the number to the desired run level. For example, to change the default run level to 3, use the following command:

sudo nano /etc/inittab

And change the line to:

id:3:initdefault:

Then save and exit the file. The changes will take effect on the next reboot.