Redhat:Runlevel control

Runlevel Control

While the run levels are generally defined, the specific services that are started up in each run level can be controlled.

Each run level has a direcotry which defined the services to be started. As an example for run level 3, the directory /etc/rc3.d defines the services.

When the system is started a command is run which will locate the run levels directory. The loop defined in the /etc/rc.d/rc file will start each script in turn. The files are named K<number><service> and S<number><service>. The services are started in order starting with the K files and then the S files.

exec /etc/rc.d/rc $RUNLEVEL

Stop a script booting for a run level

There are two ways to change which services are booted for a run level.

Manual changes

Rename the service file in /etc/rc.d/rc<runlevel> from S* or K* to something else.

Command Line Changes

Use the chkconfig command to check and change the run levels

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

chkconfig <service> on #turn a service on for run levels 2-5
chkconfig <service> off #turn a service off for run levels 2-5
chkconfig  --level 4 <service> on #turn a service on for run level 4