Kill the power faster than poweroff?

Ariel Sabiguero asabigue at
Thu Sep 11 06:19:38 EDT 2003

How about

     halt -p -f


     poweroff -f
I tried it and it takes 3s instead of 20 or more :-)

 From the man page:

       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 cur­
       rent 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.

It seems that it performs the sync call BEFORE killing the system but I 
think you should be careful.



David Mathog wrote:

>Is there a faster way to shutdown a system and kill
>the power than "poweroff"?  This is for use in
>emergency overheating conditions, where something
>that's effectively the equivalent of:
>  % sync
>  [turn off the power supply]
>is desired.
>lm_sensors and mondo are running on our Athlon 2200MP
>cluster and I'm concerned that in the event of a
>catastrophic failure of the cooling system the CPUs
>might overheat before the poweroff sequence completes.
>Not necessarily flame out immediately, but at least
>get hot enough so that they no longer run correctly,
>then poweroff wouldn't be able to complete, and then
>it's roasted CPU time.
>Tyan 2466 motherboards.
>This is only for emergency overheating, poweroff is
>fine for a normal shutdown.
>David Mathog
>mathog at
>Manager, Sequence Analysis Facility, Biology Division, Caltech
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