HALT(8) Linux System Administrator's 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 poweroff the system.
If halt or reboot is called when the system is not in runlevel 0 or 6, in other words when
it's running normally, shutdown will be invoked instead (with the -h or -r flag). For more
info see the shutdown(8) manpage.
The rest of this manpage describes the behaviour in runlevels 0 and 6, that is when the
systems shutdown scripts are being run.
-n Don't sync before reboot or halt.
-w Don't actually reboot or halt but only write the wtmp record (in the /var/log/wtmp
-d Don't write the wtmp record. The -n flag implies -d.
-f Force halt or reboot, don't call shutdown(8).
-i Shut down all network interfaces just before halt or reboot.
-h Put all harddrives on the system in standby mode just before halt or poweroff.
-p When halting the system, do a poweroff. This is the default when halt is called as
If you're not the superuser, you will get the message `must be superuser'.
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 hasn't 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 reboot.
The -h flag puts all harddisks in standby mode just before halt or poweroff. Right now
this is only implemented for IDE drives. A side effect of putting the drive in standby
mode is that the write cache on the disk is flushed. This is important for IDE drives,
since the kernel doesn't flush the write-cache itself before poweroff.
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)