halt - Unix, Linux Command

NAME

halt, reboot, poweroff - stop the system.

SYNOPSIS

/sbin/halt [-n] [-w] [-d] [-f] [-i] [-p] [-h]
/sbin/reboot [-n] [-w] [-d] [-f] [-i]
/sbin/poweroff [-n] [-w] [-d] [-f] [-i] [-h]

DESCRIPTION

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.

OPTIONS

Tag	Description
-n	Don’t sync before reboot or halt. Note that the kernel and storage 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.

DIAGNOSTICS

If you’re not the superuser, you will get the message ‘must be superuser’. Users logged in locally on the console can call halt, reboot, and poweroff without supplying the root password, due to pam_console (8).

NOTES

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.

AUTHOR

Miquel van Smoorenburg, miquels@cistron.nl