-
4: Normal mode
-
6: Reboot system
-
1: Single-user mode
-
3: Multi-user mode with networking
EXPLANATION
A Linux run level defines the state of the system after boot.
Conventionally, seven run levels exist, numbered from zero to six. They
include:
0: Halt system
1: Single-user mode
2: Basic multi-user mode without NFS
3: Multi-user mode with networking
4: Unused
5: Multi-user mode with GUI
6: Reboot system
SOURCE