System reboot command under Linux
About init command :
init 0 : Shutdown (goes thru the /etc/rc0.d/* scripts then halts)
init 1 : Single user mode or emergency mode means no network no multitasking is present in this mode only root has access in this runlevel
init 2 : No network but multitasking support is present .
init 3 : Network is present multitasking is present but with out GUI .
init 4 : It is similar to runlevel 3; It is reserved for other purposes in research.
init 5 : Network is present multitasking and GUI is present with sound etc.
init 6 : This runlevel is defined to system restart.
About shutdown command :
Schedule the system to shut down at 8 A.M.
Schedule the system to shut down at 8 P.M.
shutdown +15 "Upgrading hardware, downtime should be minimal"
Schedule the system to shut down in fifteen minutes. Along with the normal message alerting users that the system is shutting down, they will be given the descriptive message about a hardware upgrade.
Bring down the system immediately.
shutdown -r now
Bring down the system immediately, and automatically reboot it.
shutdown -P now
Bring down the system immediately, and automatically power off the system.