How do I do a COLD Reboot on FreeBSD?

Jerry McAllister jerrymc at
Mon Jan 31 07:58:34 PST 2005

> Jerry McAllister wrote:
>  >>I need to do a cold restart.  I've looked through a lot of docs, and I
>  >>can't
>  >>seem to find this out.  The computer I am working with seems to no longer
>  >>enjoy a warm reboot (like "shutdown -r now" or "reboot") but I'm pretty
>  >>sure
>  >>it will do cold reboots fine.  Is there a port, or is the shutdown command
>  >>hackable for this, or what?
>  >>
>  >>I remember many computers in bygone years which had this problem. It was
>  >>pretty common back in the 90's it seems like.  Computers would reboot and
>  >>act
>  >>weird using CTRL-ALT-DELETE, but work fine when powered off and on.
>  >
>  >
>  > FreeBSD is pretty good about doing a very clean reboot as far as the OS
>  > is concerned.  But, it is possible that some devices don't clean up well
>  > in ways that are out of FreeBSD control.    So, a "cold boot" can be a
>  > good idea in some circumstances.
>  >
>  > To do this, do a 'shutdown -h now'  or a 'shutdown -p now'  if your
>  > hardware supports the -p and you have it set up.   Choose your own
>  > time of delay for 'now' if you have other people on the machine.
>  >
>  > If you did the '-h' or the '-p' didn't turn off the power, then
>  > at the "press any key to reboot" prompt, turn off the power.
>  > Then, unplug the power source and let it set for a few minutes to let
>  > any charge dissipate.   This can be important because the capacitance
>  > in some of the devices including the power supply can provide just
>  > enough charge to keep them from reloading if that is their inclination
>  > and you lose the effect you are looking for.   You should also unplug
>  > the network connection and any external devices that have their own
>  > power supply.
> I know that this is all very good advice and information from the shutdown 
> man page and good stuff about the nature of capacitors, but all of this is 
> known to myself and unfortunately not useful...  The shutdown -p does 
> essentially a different thing (and one time it caused the freeze problem to 
> disappear.) but this also does not work.  I don't want to shut the computer 
> off, anyway, I want it to reboot back to FreeBSD remotely if need be.
> And so far, the halt command (or its shutdown -h equivalent) is not what I 
> want, either.  If I press a key to reboot, I get the same issue anyway. 
> There's a remote possibility that the halt code is causing the freeze up, 
> because FreeBSD 4.7 did not have this problem.  I'm not confident whether the 
> machine broke or the new 5.3 code broke, so I won't speculate which.  I just 
> need the reboot code.
> ...
>  > After a sufficient time drain capacitance - I usually go to the bathroom
>  > or go get something to drink to kill a few minutes - , then just plug
>  > it all back in.  Plug in the network cable and any external devices first
>  > and then the power cord and turn it on and let it boot.
> It's not the capacitors, but perhaps some strange bug in the BIOS or 
> something, I guess.  The issue that I'm highlighting is that when a floppy 
> program does a cold reset of this machine, the system (re)boots normally.

Well, I guess I completely do not understand what you are asking.
>From anything I can get from what you write here, its behavior is
normal and expected.   What is the problem and what are you trying 
to fix or to get it to do?

A cold boot - which is what you ask about in your original post - is
a boot all the way up from a powered off machine as far as I know.
So, all I did was explain how to get what you asked for in the post.

Another small guess - are you looking for  'shutdown -r now' by
any chance?

If you want something else, you will need to explain that.   Who knows
if anyone will know what to do about that - at least not until you
reveal what it is.


> As a side note, I have run this machine through the ringer trying to discover 
> any hardware errors.  The memory is now EDO ECC (it had been something else) 
> and the problem persists.  I have run diagnostics, memtest86, etc.  Futile. 
> The cold reset code exists somewhere.  Anybody?
> Billy
>  >
>  > Voila, you have gone from warm to cold to warm again.
>  >
>  > ////jerry
>  >
>  >
>  >>The computer I've got actually fails a memory test during the warm reboot.
>  >>This freezes it.  I have to power cycle the machine.  And then, the computer
>  >>performs a warm restart, bypassing its memory checks!  One more power cycle
>  >>laster, it will boot normally.  If I don't do this last reboot, the FreeBSD
>  >>boot loader or the beginning of the kernel boot crashes very early.  It's
>  >>stable otherwise on a cold reboot.
>  >>
>  >>Thanks,
>  >>Billy
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