[systemd-devel] Problems running services on system shutdown before umount

[Mads Kiilerich]

I would like to write to a log file on a local file system on system 
shutdown (or just before).

I have problems getting that right. It seems like the file systems often 
get unmounted before my service is executed. I guess it is the special 
umount.target that is umounting?

poweroff.service (and reboot) has
   Requires=shutdown.target umount.target final.target
and final.target has
   After=shutdown.target umount.target


A oneshot service referenced in shutdown.target.wants works, but when it 
is invoked the filesystems has already been unmounted and I can't do much.

The service works correctly if I remove the requirement for 
umount.target from the poweroff service(s) with this ugly hack:
   sed -i 's,umount.target,,g' /lib/systemd/system/*.service
- which confirms that it really is the umount target that triggers the 
unmounting.

But adding
   Before=umount.target
to my service makes no difference.

Is umount.target special in this regard? Or is it just that 
umount.target already has been started in parallel with shutdown.target?

If so: is it really intended that shutdown.target and umount.target 
should run in parallel without any synchronization?


If I instead reference my service in umount.target.wants then it is not 
invoked.

Is umount.target special in this regard? Is it not possible to hook 
anything on to it?


Looking at other services running at shutdown I don't see any tricks 
that seems to ensure that it is run before umount.


Can you give a hint to help me understand what is going on and how to 
get it right?

I'm using systemd-37-3.fc16.

/Mads