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06-Run-Levels.md

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Run Levels

Systemd Targets (Run Levels)

We can setup the server to boot either into graphical mode or non-graphical mode. Linux can run in multiple modes and these modes are set by something called runlevel

  • The operation mode which provide a graphical interface is called runlevel 5

  • The operation mode which provide a non-graphical mode is called runlevel 3

    run-levels

To see the operation mode run in the system. Run the command runlevel from the terminal

$ runlevel

During boot, the init process checks the runlevel, it make sure that all programs need to get the system operation in that mode are started.

  • For example: The Graphical User mode requires a display manager service to run for the GUI to work, however this service is not required for the non-graphical mode

    run-levels1

In the boot process section, we saw that the systemd is used as the init process in most new linux distributions suchs as Ubuntu 18.04.

  • In systemd, runlevels are called as targets.

    • The RunLevel 5 is called as the graphical target

    • The Runlevel 3 is called as the multiuser target

      run-levels2

Now that we are familiar with runlevels in systemd target unit. Lets now take a look at how we change these values from a shell.

To see the default target, run the command systemctl get-default. This command looks at the file located at /etc/systemd/system/default.target

$ systemctl get-default

To change the default target, we can make use of systemctl set-target <desired target name goes here as an argument>

$ systemctl set-default multi-user.target