systemd questions

[Robert Nichols]

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.

-- 
Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.