System Run level or INIT Process

System Run level or INIT Process-

INIT

· Looks at the /etc/init tab file to decide the Linux run level.

· Following are the available run levels

  0 – halt

  1 – Single user mode

  2 – Multiuser, without NFS

  3 – Full multiuser mode

  4 – unused

  5 – X11

Runlevel programs :

  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.

  Run level 0 – /etc/rc.d/rc0.d/

  Run level 1 – /etc/rc.d/rc1.d/

  Run level 2 – /etc/rc.d/rc2.d/

  Run level 3 – /etc/rc.d/rc3.d/

  Run level 4 – /etc/rc.d/rc4.d/

  Run level 5 – /etc/rc.d/rc5.d/

  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 killed.

•  ex:- S12syslog is to start the syslog deamon, 

          S80sendmail is to start the sendmail daemon, 

          syslog program will be started before send mail.