System administration command: turns off the computer. Inserts a note in the file /var/log/wtmp; if the system is in runlevel 0 or 6, stops all processes; otherwise, calls shutdown -h.
Suppress writing to /var/log/wtmp.
Call halt even when shutdown -nf would normally be called (i.e., force a call to halt, even when not in runlevel 0 or 6).
Place hard drives in standby mode before halt or power off.
Shut down network interfaces before halt.
No sync before reboot or halt.
Perform power-off when halting system.