[Nut-upsuser] [systemd-devel] Trying to turn off a UPS with home-made service unit

[Michal Hlavinka]

On 09/15/2013 04:30 PM, Roger Price wrote:
> Here is the effect on a simple openSUSE 12.3 test rig of replacing my
> home-made service unit /lib/systemd/system/ups-delayed-shutdown.service
> with a script in the /usr/lib/systemd/system-shutdown/ drop-in
> directory. I used the default UPS offdelay of 20 secs. The X's indicate
> the race window. (Sorry for the ascii art.)
>
> 1) My "bad idea" ups-delayed-shutdown.service
>
> systemctl               system
> poweroff                 halt
>     |     |XXXXXXXXXXXXXXXX|
>     0   2 | 4   6   8  10  12  14  16  18  20  22  24  26  28  30  32 secs
>           |                                       |
>        upsdrvctl                                 UPS
>        shutdown                                shutdown
>
> 2) Replaced by script in /usr/lib/systemd/system-shutdown/
>
> systemctl               system
> poweroff                 halt
>     |                 |XXXX|
>     0   2   4   6   8 |10  12  14  16  18  20  22  24  26  28  30  32 secs
>                       |                                       |
>                   upsdrvctl                                  UPS
>                   shutdown                                 shutdown
>
> The script solution has the advantage of reducing the race window from 9
> to 3 secs.  Note that the same security can also be achieved by the
> service unit by setting offdelay = 26 in ups.conf.  My script is

you are wrong. The catch is that in the first case, time between 
"upsdrvctl shutdown" and "system halt" is varying. Only in your case 
it's 9 seconds. With network mounted disks it can take 100 seconds or 
more without any problem. On the other hand, in the second case 1)there 
is no task that can take a lot more time than usual, 2)nothing really 
important happens here, so even if you turn power off here, you can have 
disk that does not have parked heads, but that's no biggie and no data loss.