[systemd-devel] systemd and LSB Required/Should-Stop

[Lennart Poettering]

On Fri, 24.06.11 14:04, Ville Skyttä (ville.skytta at iki.fi) wrote:

> Hello,
> 
> Am I right that systemd does currently have no support for the LSB
> Required-Stop and Should-Stop keywords?  If yes, are there plans to
> support them in the future?

That is true, we do not support this right now. In systemd the shutdown
order is always the inverse startup order of two services. I am not
entirely opposed to make this more flexible but so far I have not heard
of a good usecase where the flexibility to detach the shutdown oder from
the startup order was necessary. 

> The use case I have is in Fedora's vdr package:
> http://pkgs.fedoraproject.org/gitweb/?p=vdr.git .  The init script's
> stop action uses rtcwake to set the next wakeup time for the box, and
> even though the implementation is hairier than I'd like, it has worked
> well for me before Fedora 15.  But with Fedora 15 and systemd it often
> fails to do its job when shutting down the system (works fine if I just
> stop vdr with the machine running), which causes my PVR box not to wake
> up when it should and consequently missed timed recordings which is very
> annoying.
> 
> The way the init script's stop action handles setting the wakeup time is
> that it looks up the time to set from the /var/run/vdr/next-timer file
> which may or may not be present; if it's not, it grabs the time using
> SVDRP (a simple TCP based protocol) from localhost, and finally if it
> gets the time from one of these sources, writes it to the RTC with
> rtcwake.

Is there any good reason why this isn't stored in the RTC right-away,
when needed? It sounds unnecessarily complex and fragile to delay this
until shutdown.

Also, much simpler and nicer would be to use CLOCK_REALTIME_ALARM which
allows multiple clients to trigger a wakeup from suspend.

> I've done some debugging and when rtcwake fails, it fails because
> /dev/rtc0 is being handled by /sbin/hwclock (hwclock-save.service).  So
> my first thought was to add "hwclock-save" to the init script's
> Should-Stop LSB keyword but that didn't help, so I grepped systemd's
> sources for Should-Stop and found nothing.

We have now removed this unit file in git. However can you elaborate why
exactly these two service conflict when run at the same time? do you
have any error messages?

> I have some thoughts about "fixing" vdr to implement the wakeup time
> stuff better than it does now sometime in the future, but for now
> there's nothing.  Ideas for hacks/workarounds for the init script (see
> above for the gitweb link) I could use to make sure that /var/run and
> localhost networking are available at the time vdr gets stopped at
> shutdown, and that nothing's reserving /dev/rtc0 at that time (so I
> suppose $local_fs, $network, and $time/hwclock-save haven't been
> "stopped" yet)?  Note that I'm stuck with the sysv vdr init script until
> Fedora 16 (can't convert the package to native systemd before that).

If a service A and a service B are ordered against each other
(regardless in which way) then systemd will ensure that when one is
started and the other is stopped, the stopping is done first and the
starting second. That means you can just add any kind of ordering dep
between the two, and things should work.

Lennart

-- 
Lennart Poettering - Red Hat, Inc.