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Re: problematic poweroff on shutdown

Curt wrote:
> Bob Proulx wrote:
> > Power-off hang.  Reboot hang.  Neither worked.  They are the same
> > thing.  Both actions could not control the power supply from software.
> Well, now I'm confused.  I might have a reboot problem and not know
> about it in the sense that I hardly ever reboot (I think the only linux
> reboot that was ever required of me in the course of my usage of the OS
> was after a kernel update).  
> Now you say rebooting requires and entails the exact same electrical
> event as a poweroff?  I don't quite understand.  You mean that reboot
> powers off the machine, and then turns it back on again immediately,
> whereas a shutdown/poweroff simply powers the machine off?  

Isn't that the way that it works?  I always thought that it did.  All
of the behavior indicates to me that it does.  But I could easily be
wrong about it.  Perhaps one of our loyal readers will know the answer
off the top of their head and will type in a response concerning
actual power supply operation.  Otherwise I will need to put a probe
on the power pins and determine the answer by looking.

With the AT power standard computers only had the big "clunk" switch
and that was the only way to power them off.  With the introduction of
the ATX power standard this became software controllable.  But
remember that there is always the +5V standby power which is always on
regardless of other settings.  In addition there is the Power Good
signal which acts as a hardware reset signal.  When the supply is off
then the Power Good signal is off.  Power Good should pause a few
milliseconds before signaling good to allow the power supply to
stabilize.  Those signals come from the power supply to the computer
circuitry.  Going from the computer circuitry to the power supply is
the Power On signal.  Pulling the power on signal low signals the
supply to turn on.  And bringing it high will turn it off.  Moving the
signal high and then low again will cause the supply to turn off and
then back on again and the Power Good signal will send a reset.

> I'm talking soft reboot here, "shutdown -r now".
> You must surely be talking hard reboot?  I turn off my machine once a day, at
> night.  There have been no problems turning it back on again, no hangs on
> "rebooting" (hard).

I was talking about both 'shutdown -h now' and 'shutdown -r now'
behavior.  It didn't matter.  Both would hang.  Upgrading the BIOS
solved the problem.  The note says: "Fixed Linux reboot failure."


Rebooting *is* very important.  The Linux kernel routinely has
security upgrades published for it.  After installing the new security
patch kernel it is important that the system be rebooted to the new
kernel so that the security vulnerability is mitigated.  I definitely
want my systems to be able to reboot unattended.

> Sorry for leading you down this trail of confusion.

Happy trails! :-)


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