How do I do a COLD Reboot on FreeBSD?

Niy Niy at
Mon Jan 31 13:18:55 PST 2005


-----Original Message-----
From: owner-freebsd-questions at
[mailto:owner-freebsd-questions at] On Behalf Of Bart Silverstrim
Sent: Monday, January 31, 2005 3:30 PM
To: Billy Newsom
Cc: freebsd-questions at
Subject: Re: How do I do a COLD Reboot on FreeBSD?

On Jan 31, 2005, at 1:53 PM, Billy Newsom wrote:

> Jerry McAllister wrote:
>> 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.
> No, I said a cold reboot.  That's the term for a reboot which runs the 
> entire POST, counts memory, etc.  The screen looks identical to a cold 
> start or cold boot.  We all know what the warm reboot means -- that's 
> when many parts of the POST are skipped.  Windows uses a cold reboot, 
> for example, when you click "Restart" on the Shutdown menu.  FreeBSD 
> does a warm reboot using the reboot command.  The warm reboot may save 
> thirty to sixty seconds over the cold reboot.  A warm reboot typically 
> skips the memory check and does a cursory check of hard drive 
> parameters, etc. to save time.
> If you use a PC DOCTOR disk and tell it to reboot, it will do a cold 
> reboot.  When you flash your BIOS from DOS, it will usually do a cold 
> reboot when it exits.  When you save changes and reboot from the BIOS 
> setup screen, it will do a cold reboot.  Many other examples are 
> possible.
> What I tried to explain is that this PC crashes on the subsequent boot 
> if a warm reboot is performed by FreeBSD.  But if I could perform a 
> cold reboot every time, this would solve the issue.  A cold reboot is 
> not the act of "shutting the power off and turning it back on."  That 
> is called a power cycle and it is obviously manual.  A cold reboot is 
> done by a special software command.
>I was always told a cold reboot comes from powering down the system;
minimal power to the logic board and wiping any and all traces 
>possible (short of unplugging it) of random crap in the capacitors and
>Literally cold boot because usually it happened after powering it down and
it would cool off until the user came back to work on their >computer for
>Warm boots basically just cycle the computer to restart the OS.  It's just
restarting it, and power to the components has been 
>maintained the whole time so as far as the computer hardware is concerned
nothing really happened, just a chunk of memory access and the >processor
mode getting kicked around a bit.
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Okay, you're all mostly correct. For more info, see this page:

Now, as for how to get FreeBSD to set this area in memory (0000:0472h) set
with the something other than 1234h, I'd imagine a simple assembler job
could do it. Seems right up assemblers alley. It's been a while since I've
done anything outside of C, but I'll see what I can whip up.

- Niy

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