4.3 About Run Levels

Run levels allow you to start a system with only the services that are required for a specific purpose. For example, a server can run more efficiently at run level 3, because it does not run the X Window System at that run level. It is best to perform diagnostics, backups, and upgrades at run level 1 when only root can use the system. Each run level defines the services that init stops or starts. For example, run level 3 starts network services and run level 5 starts the X Window System, whereas run level 1 stops both of these services.

The following run levels are defined by default under Oracle Linux:

0

Halts the system.

1

Single-user text mode.

2

Full multiuser text mode without NFS support.

3

Full multiuser text mode with NFS support.

4

Not used, but can be user defined.

5

Full multiuser graphical mode with an X-based login screen.

6

Reboots the system.