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HALT(8) Linux System Administrator's Manual HALT(8)


halt, reboot, poweroff - stop the system


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


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 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 behavior in runlevels 0 and 6, that is when the systems shutdown scripts are being run.


Don't write the wtmp record.
Force halt or reboot, don't call shutdown(8).
Put all hard drives on the system in stand-by mode just before halt or power-off.
Shut down all network interfaces just before halt or reboot. Warning: This may not work on interfaces which do not have an IP address and should ideally be handled by a network manager service.
Try to reboot using kexec, if kernel supports it.
Don't sync before reboot or halt. Note that the kernel and storage drivers may still sync. This implies -d.
When halting the system, switch off the power. This is the default when halt is called as poweroff.
Don't actually reboot or halt but only write the wtmp record (in the /var/log/wtmp file).


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 and /var/run/runlevel does not exist) 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 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 doesn't 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


shutdown(8), init(8)

November 6, 2001 sysvinit