You can use the chkconfig command to define in which run levels a service should run, to list startup information for services, and to check the state of services. chkconfig changes the configuration of the symbolic links in the /etc/rcN.d directories.

To list the run-level configuration of all services that run their own daemon:

# chkconfig --list
NetworkManager 	0:off	1:off	2:on	 3:on	4:on	 5:on	6:off
abrt-ccpp      	0:off	1:off	2:off	3:on	4:off	5:on	6:off
abrt-oops      	0:off	1:off	2:off	3:on	4:off	5:on	6:off
abrtd          	0:off	1:off	2:off	3:on	4:off	5:on	6:off
acpid          	0:off	1:off	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
...

The command lists each service, followed by its configured state for each run level. For example, the abrtd service is configured to run at run levels 3 and 5.

To view the configuration of a particular service, such as ntpd, specify its name as an argument:

# chkconfig --list ntpd
ntpd           	0:off	1:off	2:on	3:on	4:on	5:on	6:off

To enable a service to run at run levels 2,3, 4, or 5, use the on argument:

# chkconfig httpd on
# chkconfig --list httpd
httpd          	0:off	1:off	2:on	3:on	4:on	5:on	6:off

To enable the service for certain run levels only, specify the --level option followed by a concatenated list of the run levels, for example:

# chkconfig --level 35 httpd on
# chkconfig --list httpd
httpd          	0:off	1:off	2:off	3:on	4:off	5:on	6:off

Similarly, the off argument disables a service for run levels 2, 3, 4, and 5, or for the run levels specified by --level, for example:

# chkconfig sshd off
# chkconfig --list sshd
sshd           	0:off	1:off	2:off	3:off	4:off	5:off	6:off
# chkconfig sshd on
# chkconfig --list sshd
sshd           	0:off	1:off	2:on	3:on	4:on	5:on	6:off
# chkconfig --level 34 sshd off
# chkconfig --list sshd
sshd           	0:off	1:off	2:on	3:off	4:off	5:on	6:off

The chkconfig command changes the configuration of a service to run at a particular run level. It does not change the current state of a service as this example shows:

# runlevel
N 5
# chkconfig sshd off
# chkconfig --list sshd
sshd           	0:off	1:off	2:off	3:off	4:off	5:off	6:off
# service sshd status
openssh-daemon (pid  12101) is running...

The changed configuration of the sshd service takes effect only when you next change the system's run state, for example, by rebooting the system. You could, of course, use the service sshd stop command to stop the service.

For more information, see the chkconfig(8) manual page.