Linux it has the six run level. For run level 0 to run level 6. I mention in that screen shot. For run level 0 is turn off, Run level 1: it is mainly used by the system administrator. It is used for system maintains and repairing process. It is also called “single user mode”.2 for multi user mode without network, 3 for multi user mode with network, 4 it is unused ,5 for graphical mode , for run level 6 it is turn off.
If you like to see there run level file in Linux or centos go to following directory
#cd /etc/inittab
There default run level specified in the line 18
Id:3:intdefault; it is refers to the default run level is 3 by through editing these line you change run level
You can view the all the run level by though following Linux chkconfig command
#chkconfig --list
In the Booting process all the service are running under runlevel 3- “ multi user mode with network”
Linux Run Level Directory
0 /etc/rc.d/rc0.d
1 /etc/rc.d/rc1.d
2 /etc/rc.d/rc2.d
3 /etc/rc.d/rc3.d
4 /etc/rc.d/rc4.d
5 /etc/rc.d/rc5.d
6 /etc/rc.d/rc6.d
In the every run level specific directory it contain the particular run level service.
What are service are need to run under the run level. Here all the files have the soft link to the /init.d/command name.
Here you can see each file stat with “s” means script should be run at startup.“k” means script should be run when the system is shutting down.
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