Runlevel is the operating system state on Linux system (it dictates the state that the machine is currently operating, and what applications or services can run at that time). There are seven (7) run levels numbered from 0 to 6. A system can be booted into any of the given runlevel. Runlevels are identified by numbers.

Checking the Default Runlevels on Linux Systems

Furthermore, a system boots either to runlevel 3 or to runlevel 5. Runlevel 3 is CLI, and 5 is GUI. However, There are different commands that can show the current run level state on a server.

Who Command

who -r

Systemctl Command

systemctl get-default

Using /etc/inittab File
– Moreover, The default runlevel for a system is specified in the /etc/inittab file

cat /etc/inittab

Using /etc/systemd/system/default.target File

In addition, The default runlevel for a system is specified in the /etc/systemd/system/default.target file for systemd System.

Nonetheless, The following details show what each of the default runlevels represent. These are the standard definitions which may be slightly different depending on your Linux distribution.

0 – Set the runlevel to 0, and your machine halts.
1 – Single-user Mode serves administrative tasks before launching non-essential services.
2 – is the first multi-user mode runlevel and will start some non-essential services. This may, or may not contain networking depending on your Linux distribution.
3 – is a multi-user mode which headless servers usually run at. All essential and non-essential services such as Apache HTTP Server should be running.
4 – The default operating system does not use this multi-user mode runlevel; you can use it for user-defined purposes.
5 – GUI desktops like Gnome or KDE load during this stage.
6 – Runlevel 6 issues a reboot command, causing the operating system to restart.

I hope you found this blog post helpful. If you have any questions, please let me know in the comment session.