systemd questions

[Simo Sorce]

On Wed, 2011-05-18 at 16:48 -0500, Robert Nichols wrote:
> On 05/18/2011 04:04 PM, Lennart Poettering wrote:
> > Host requests power down from UPS in 30s. Host then continues shut
> > down. If the host now ends up taking more time then expected for
> > shutting down it might still be busy at the time of the power going
> > away. It's a race between "UPS powering off" and "system finishing
> > shutdown". It's a bet that your system is faster than 30s when
> > unmounting the remaining file systems, syncing the MD/DM metadata to
> > disk, syncing ATA and so on (i.e. all the stuff the kernel does when you
> > invoke the reboot() syscall).
> 
> Here's another race.  Host requests power down from UPS in 30s.  Host
> completes shutdown.  At some point during that 30s interval, commercial
> power is restored.  Result: Host shuts down and never restarts.  Sorry
> about that.
> 
> The way I've always prevented that is to have the host do a reboot,
> not a shutdown, but send an immediate shutdown command to the UPS
> just before sending control to the BIOS for the reboot.

What you should do is to configure the BIOS to always boot on power-up.

This way the UPS will remove power, figure out power is returned,
reapply power and the BIOS will reboot the machine.

That's how this problem should normally be handled, then there is the
reality of broken BIOSes, broken UPSs, and general unlucky
circumstances :)

Simo.

-- 
Simo Sorce * Red Hat, Inc * New York