See also upstart if you are using ubuntu.
You can start and stop installed daemons such as 'ntp' (network time protocol -- this will synchronize your clock) by running the start and stop scripts in /etc/init.d/
# /etc/init.d/ntp start ntpd: time slew -0.014128s Starting network time protocol daemon (NTPD) done # /etc/init.d/ntp stop Shutting down network time protocol daemon (NTPD) done
To have this turn on automatically when the server is rebooted you need to know about runlevels. A runlevel is a mode the server is currently in. You can see the different levels in /etc/inittab.
My box has the following:
runlevel 0 is System halt (Do not use this for initdefault!) runlevel 1 is Single user mode runlevel 2 is Local multiuser without remote network (e.g. NFS) runlevel 3 is Full multiuser with network runlevel 4 is Not used runlevel 5 is Full multiuser with network and xdm runlevel 6 is System reboot (Do not use this for initdefault!)
To see the current runlevel, use the runlevel command.
# runlevel N 5
This tells us we are in runlevel 5.
To change the daemons to be stopped or started at different runlevels, use the chkconfig program.
To turn on ntp when runlevel 5 is reached, run:
# chkconfig ntp 5