Unix for Beginners
Unix Shell Programming
Unix Useful References
Unix Useful Resources
Copyright © 2014 by tutorialspoint
halt - Unix, Linux Command
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 its 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.
Dont sync before reboot or halt. Note that the kernel and storage
drivers may still sync.
Dont actually reboot or halt but only write the wtmp record
(in the /var/log/wtmp file).
Dont write the wtmp record. The -n flag implies -d.
Force halt or reboot, dont call shutdown(8).
Shut down all network interfaces just before halt or reboot.
Put all harddrives on the system in standby mode just before halt or poweroff.
When halting the system, do a poweroff. This is the default when halt is
called as poweroff.
If youre 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).
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 hasnt 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 doesnt 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