Runlevel programs2 min read
When the Linux system is booting up, you might see various services
getting started. For example, it might say “starting sendmail …. OK”.
Those are the runlevel programs, executed from the run level directory
as defined by your run level.
Depending on your default init level setting, the system will execute the
programs from one of the following directories. o Run level 0 – /etc/rc.d/rc0.d/
o Run level 1 – /etc/rc.d/rc1.d/
o Run level 2 – /etc/rc.d/rc2.d/
o Run level 3 – /etc/rc.d/rc3.d/
o Run level 4 – /etc/rc.d/rc4.d/
o Run level 5 – /etc/rc.d/rc5.d/
o Run level 6 – /etc/rc.d/rc6.d/
– Please note that there are also symbolic links available for these
directory under /etc directly. So, /etc/rc0.d is linked to /etc/rc.d/rc0.d.
– Under the /etc/rc.d/rc*.d/ directories, you would see programs that
start with S and K.
– Programs starts with S are used during startup. S for startup.
– Programs starts with K are used during shutdown. K for kill.
– There are numbers right next to S and K in the program names. Those
are the sequence number in which the programs should be started or
For example, S12syslog is to start the syslog deamon, which has the
sequence number of 12. S80sendmail is to start the sendmail daemon,
which has the sequence number of 80. So, syslog program will be started
Different types of run levelslinux
There are 7 different run levels present (run level 06) in Linux system for
different purpose. The descriptions are given below.
0: Halt System (To shutdown the system)
1: Single user mode
2: Basic multi user mode without NFS
3: Full multi user mode (text based)
5: Multi user mode with Graphical User Interface
6: Reboot System