Starting and Stopping Daemons with runlevel

The startup scripts I have been mentioning in the /etc/init.d directory govern the activation of daemons that were installed with some of your Linux packages. The commands to start and stop them are universal.
Starting a Daemon
If a startup script exists in the /etc/init.d directory, then its daemon can be started by specifying its filename followed by the keyword "start" as seen here:

root@u-joshi:~# /etc/init.d/apache start
 * Starting apache 1.3 web server...
   ...done.
root@u-joshi:~#

Stopping a Daemon

Daemons can be stopped by specifying its script filename followed by the keyword "stop":

root@u-joshi:~# /etc/init.d/apache stop
 * Stopping apache 1.3 web server...
   ...done.
root@u-joshi:~#

Restarting a Daemon

Daemons usually only read their configuration files when they are started, therefore if you edit the file, you have to restart the daemon for the new settings to become active. This can be done with the keyword "restart":

root@u-joshi:~# /etc/init.d/apache restart
 * Restarting apache 1.3 web server...
   ...done.
root@u-joshi:~#

chkconfig command can be used to adjust which applications start at each runlevel.

[root@joshi joshi ]# chkconfig --list
keytable 0:off 1:on  2:on  3:on 4:on  5:on 6:off
atd      0:off 1:off 2:off 3:on 4:on  5:on 6:off
syslog   0:off 1:off 2:on  3:on 4:on  5:on 6:off
gpm      0:off 1:off 2:on  3:on 4:on  5:on 6:off
kudzu    0:off 1:off 2:off 3:on 4:on  5:on 6:off
wlan     0:off 1:off 2:on  3:on 4:on  5:on 6:off
sendmail 0:off 1:off 2:off 3:on 4:off 5:on 6:off
...
...

[root@joshi  joshi ]# chkconfig --list | grep mail
sendmail 0:off 1:off 2:off 3:on 4:off 5:on 6:off
[root@joshi joshi ]#
The chkconfig command can be used with grep to determine the run levels in which sendmail will run. Here we see it will run at levels 3 and 5. 

[root@joshi  joshi ]# chkconfig --list | grep mail
sendmail 0:off 1:off 2:off 3:on 4:off 5:on 6:off
[root@bigboy joshi ]#