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)
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. Note that the kernel and stor-
age drivers may still sync.
-w Don't actually reboot or halt but only write the wtmp record (in
the /var/log/wtmp file).
-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 poweroff.
If you're not the superuser, you will get the message 'must be supe-
ruser'. Users logged in locally on the console can call halt, reboot,
and poweroff without supplying the root password, due to pam_console
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
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
shutdown(8), init(8), pam_console(8)
Nov 6, 2001 HALT(8)