Linux Administration - Runlevels

Levels 

0 	- shutdown system (complte power down)
1,s,S 	- single user mode
2 	- full multi-user mode [text] (Debian)
3 	- full multi-user mode [text] (Fedora, Mandrake and Red Hat)
4 	- undefined
5 	- full multi-user mode [X] (Fedora, Mandrake, Red Hat, etc)
6 	- reboot

Files 
/etc/inittab
format: id:runlevels:action:process
Once all entries in inittab for systems runlevel is executed, the boot process is complete.

/etc/init.d/rc
/etc/init.d/rc.d			
/etc/rc.d
SysV startup scripts are stored in these directories, depending on distribution.

Commands 
/etc/init.d/smd start
Manually start the samba server.

[top] chkconfig

chkconfig --list [service]
Lists the current services running and their runlevels. Specify a particular service to view the results for that service only.

chkconfig --level [levels 0-6] [service] [on/off/reset]

> chkconfig --level 2345 [service] off
Manipulate the current runlevels for a service.

chkconfig --add [service]
After adding a startup script to the SysV startup directory, add start/stop links in runlevel directories. Make sure the comment lines in the script have the proper syntax for chkconfig's use.

chkconfig | grep -v off
Check for all processes that are on.

[top] ntsysv (Red Hat, Fedora and Mandrake)

ntsysv [--level] [levels 0-6]
Configure runlevels.
If no options specified the current runlevel will be managed.

[top] runlevel

 runlevel
N 2
Display runlevel information.
The first field is the previous run level..
The second field is the current run level. "N" means the runlevel has not switched since boot.

[top] init / telinit

 init [runlevel]
Change system runlevel.

 telinit [runlevel, q]
Change system runlevel. Specify "q" if changes were made to /etc/inittab so it can be re-read.

 sync;sync; init 6 OR reboot
Reboot but first flush buffers to hard disk

[top] service

 service --status-all | grep -v stopped
Change system runlevel.

[top] shutdown

 shutdown now
Change system runlevel to 1. Shutdown immediately!

 shutdown -r +5 "rebooting in 5 minutes"
Reboot system in 5 minutes and display message

 shutdown -h +15 "shutting down in 15 minutes"
Halt system in 15 minutes and display message.

 shutdown -c "shutdown cancelled"
Cancel shutdown and display message.

[top] halt/reboot/poweroff

 halt
Shutdown system.

 reboot
Reboot system.

 poweroff
Shutdown and power off system.