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HALT

Section: Linux System Administrator's Manual (8)
Updated: Nov 6, 2001
Index Return to Main Contents

NAME

halt, reboot, poweroff - stop the system

SYNOPSIS

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

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 powe-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.

OPTIONS

-d: Don't write the wtmp record.
-f: Force halt or reboot, don't call shutdown(8).
-h: Put all hard drives on the system in stan-by mode just before halt or powe-off.
-i: 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.
-k: Try to reboot using kexec, if kernel supports it.
-m: When running on a Linux system, any quoted parameter after the -m flag will be passed to the firmware to be interpreted at boot time. Some systems, like the Raspberry Pi, can use this to switch target partitions. Please note, this parameter enables -f, forcing the reboot command to handle shutting down itself.
-n: Don't sync before reboot or halt. Note that the kernel and storage drivers may still sync. This implies -d.
-p: When halting the system, switch off the power. This is the default when halt is called as poweroff.
-w: Don't actually reboot or halt but only write the wtmp record (in the /var/log/wtmp file).

DIAGNOSTICS

If you're not the superuser, you will get the message `must be superuser'.

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 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 powe-off. Right now this is only implemented for IDE drives. A side effect of putting the drive in stan-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 powe-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.