A run level is a state of init and the whole system that defines what system services are operating. Run levels are identified by numbers. Some system administrators use run levels to define which subsystems are working, e.g., whether X is running, whether the network is operational, and so on.
The important thing to note here is that there are differences in the runlevels according to the operating system. The standard LINUX kernel supports these seven different runlevels :
0 – System halt i.e the system can be safely powered off with no activity.
1 – Single user mode.
2 – Multiple user mode with no NFS(network file system).
3 – Multiple user mode under the command line interface and not under the graphical user interface.
4 – User-definable.
5 – Multiple user mode under GUI (graphical user interface) and this is the standard runlevel for most of the LINUX based systems.
6 – Reboot which is used to restart the system.
Note : Run Level is set with linking to /etc/systemd/system/default.target
- To show the current settings
- systemctl get-default
- change the RunLevel to Graphical-login