The standard Run Level for a linux machine booting up in full GUI mode is Run Level 5. In my experience, the most common Run Level (other than 5 for standard boot up) is Run Level 3. The most common need for Run Level 3 is for debugging problems and installing graphic drivers.
If you want to specify a default Run Level other than 5, the option can be changed in your /etc/inittab as defined by the initdefault directive. Below is a table specifying the other various Run Levels and State properties. Note that it is important never to set your initdefault directive to Run Level 0 or 6.
| Run Level | State |
|---|---|
| 0 | halt (shutdown) system |
| 1 | single user mode |
| 2 | multi user with no network exported |
| 3 | default full multi user console (text) only |
| 4 | reserved for local use (and X-window) |
| 5 | X-window full GUI mode |
| 6 | reboot system |
Change Run Level After Boot Up
The easiest way to change the Run Level after the system has already been booted up is to open up the console and use init. There is an example below on how to change the Run Level to 3.
init 3
In addition, teleinit is an alternative to init and works in exactly the same manner.
telinit 3
Change Run Level on System Boot Up
If however your Linux machine is currently powered off and you would like to boot directly into an alternative Run Level, you can change the Run Level by accessing the linux startup boot menu (GRUB). Simply choose the desired kernel and add init 3 into the kernel string.
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