Random session bus availability with systemd

[tomw]

On Fri, 2014-08-08 at 18:53 +0200, tjoen wrote:
> On 08-08-14 08:49, tomw wrote:
> > ExecStart=/usr/bin/sudo -b -u xyzuser -i /usr/bin/startx /usr/bin/master
> > [Install]
> > WantedBy=multi-user.target
> >
> > Master then starts some other processes which all start after one after
> > another upon their appearance on the session bus, i.e. process1 is
> > started as soon as process0 appears on the session bus with its well
> > known name.
> > This approach used to work reliably under sysV. 
> >
> > Moving to systemd it seems that there are some timing issues which
> > result in an random failure of the approach. The reason for that failure
> > is that sometimes process1 does not properly appear with it's name on
> > the session bus. As a result the subsequent processes do not start.
> >
> >    CGroup: /system.slice/master.service
> >            ├─544 /usr/bin/sudo -b -u xyzuser -i /usr/bin/startx /usr/bin/master
> >            ├─555 /bin/sh /usr/bin/startx /usr/bin/master
> >            ├─860 xinit /usr/bin/master -- /etc/X11/xinit/xserverrc :0 -auth /tmp/serverauth.VP0SdUCg...
> >            ├─861 /usr/bin/X -nolisten tcp :0 -auth /tmp/serverauth.VP0SdUCgVO
> >            ├─867 python /usr/bin/master
> >            ├─871 /usr/bin/dbus-launch --autolaunch fbf381267b161fcf27363a6453d687d7 --binary-syntax --...
> >            ├─872 /usr/bin/dbus-daemon --fork --print-pid 5 --print-address 7 --session
> >            ├─873 /usr/bin/python2.7 /usr/bin/process0
> >            └─882 /usr/bin/process1
> >
> > As the approach used to work with sysV it seems I'm missing some point with the session bus setup under systemd.
> >
> I understand from your story that process1 takes too long to start so
> next processes failed to start. That is because everything in
> multi-user.target
> start at the same time resulting in delays in e.g. disk read.
> Not most elegant but easiest is to put a sleep 5 after process1

To avoid any kind of dependencies on arbitrary delays the master program
is starting a subsequent process only after the name of the respective
dependency appears on the session bus. This was meant to provide an
ordered start of processes - adding a timeout would therefore not work.
The root cause must be somewhere with the setup of the session bus in
systemd context. As said the approach works well with sysV...

  
> _______________________________________________
> dbus mailing list
> dbus at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/dbus