HALT(8) Linux System Administrators Manual HALT(8)
halt, reboot, poweroff - stop the system.
/sbin/halt [-n] [-w] [-d] [-f] [-i] [-p] [-h]
/sbin/reboot [-n] [-w] [-d] [-f] [-i]
/sbin/poweroff [-n] [-w] [-d] [-f] [-i] [-h]
Halt notes that the system is being brought down in the file
/var/log/wtmp, and then either tells the kernel to halt, reboot or
power-off the system.
If halt or reboot is called when the system is not in runlevel 0 or 6,
in other words when its running normally, shutdown will be invoked
instead (with the -h or -r flag). For more info see the shutdown(8)
The rest of this manpage describes the behaviour in runlevels 0 and 6,
that is when the systems shutdown scripts are being run.
-n Dont sync before reboot or halt.
-w Dont actually reboot or halt but only write the wtmp record (in
the /var/log/wtmp file).
-d Dont write the wtmp record. The -n flag implies -d.
-f Force halt or reboot, dont call shutdown(8).
-i Shut down all network interfaces just before halt or reboot.
-h Put all hard drives on the system in stand-by mode just before
halt or power-off.
-p When halting the system, switch off the power. This is the
default when halt is called as poweroff.
If youre not the superuser, you will get the message must be supe
Under older sysvinit releases , reboot and halt should never be called
directly. From release 2.74 on halt and reboot invoke shutdown(8) if
the system is not in runlevel 0 or 6. This means that if halt or reboot
cannot find out the current runlevel (for example, when /var/run/utmp
hasnt been initialized correctly) shutdown will be called, which might
not be what you want. Use the -f flag if you want to do a hard halt or
The -h flag puts all hard disks in standby mode just before halt or
power-off. Right now this is only implemented for IDE drives. A side
effect of putting the drive in stand-by mode is that the write cache on
the disk is flushed. This is important for IDE drives, since the kernel
doesnt flush the write cache itself before power-off.
The halt program uses /proc/ide/hd* to find all IDE disk devices, which
means that /proc needs to be mounted when halt or poweroff is called or
the -h switch will do nothing.
Miquel van Smoorenburg, email@example.com
Nov 6, 2001 HALT(8)