Each runlevel designates a different system configuration and allows access to a different combination of processes. Runlevels determine how much of the systems services are actually running. If you switch to higher run levels, mean you are making additional services on or if you are moving lower level means you are switching off currently running services Most common runlevel for servers is going to be 3, most services that are not GUI oriented (including the Gnome Desktop) are turned off.
In practical environment generally linux system administrator use run level 3 .
In exam we suggest you to keep runlevel 5 as higher runlevel means more available services. Runlevel 5 is what you see when you boot into the desktop environment.
|2||Multi-user mode console logins only (without networking)|
|3||Multi-User mode, console logins only|
|5||Multi-User mode, with display manager as well as console logins (X11)|
To check current run level use runlevel command.
Switching between these levels is fairly straightforward. To switch to runlevel 3 type: init 3
to check current runlevel and last runlevel use who command with -r switch
as output show our current runlevel is 3 and last runlevel was 5
you could also use runlevel command to check the current level and last runlevel
runlevel command first show previous runlevel and later current runlevel as output show our previous runlevel was 5 and current is 3
Default runlevel is set in /etc/inittab file, during the exam you may need to change default runlevel. In real life checking default runlevel is a good point to start troubleshooting of a system which is getting reboot just after the boot or system is not getting desktop environment
locate following line,
5 is default runlevel here you could change it, but don't set to 0 or 6 as it is also suggested in file.
to switch back to graphic run init 5
in graphic you could use runlevel to check our last runlevel
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