Programs like pcmanfm, evince, ... don't connect to dbus unless run with dbus-launch

[Brendan Tildesley]

On 08/01/18 07:54, Danny Milosavljevic wrote:
> Hi,
>
> dbus is an object-oriented inter-process-communication mechanism.
>
> On a typical single-user system there's one user bus, at least one session
> bus and one system bus.
>
> On a typical multi-user system there's multiple user buses, at least as many
> session buses and one system bus.
>
> >From your messages I suspect that the dbus session bus for your session is 
> >not
> running.
>
> Try invoking
>
>  echo $DBUS_SESSION_BUS_ADDRESS
>
> .
>
> If it's empty, no session bus is running.
>
> Many many GNOME parts try to use dbus for everything (also arguably for
> things which would work perfectly well without dbus, but whatever).
>
> dbus-launch is used to start a message bus from a shell script.
>
> It's usually chained together like this (that's how I use it for real):
>
> $ exec dbus-launch ssh-agent fluxbox
>
> This means that dbus-launch will set up some environment variables,
> invoke the daemon and then invoke dbus-daemon and then invoke the
> child (here, ssh-agent, passing it "fluxbox"), passing it the environment.
>
> If you invoke "dbus-launch evince" it's starting a mini-session bus
> and in there invokes evince.  Evince then cannot connect to the other
> services in your session (because there are no other such services in
> this mini-session).
>
> I think modifying the slim service to use dbus-launch when starting
> the session should have worked just fine.
>
>>> I tried modifying the slim service to launch the session with
>> dbus-launch, but that only served to create some new errors when running
>> pcmanfm:
> Yes, but what does
>
>   echo $DBUS_SESSION_BUS_ADDRESS
>
> say now?
>
>> invoking IsSupported() failed for remote volume monitor with dbus name
>                                     ^^^^^^ ???
>
> Also, here, it's not finding lots of service files.  Something needs to make
> sure that the dbus daemon finds the service files.  Usually we have an 
> environment
> variable for that (see further below).
>
> There are system services in /etc/dbus-1/system-services which should be 
> found in
> all cases.
>
> Among those is org.freedesktop.UDisks2 which is not 
> org.gtk.vfs.UDisks2VolumeMonitor .
>
> org.gtk.vfs.UDisks2VolumeMonitor is not in the directory 
> /etc/dbus-1/system-services .
>
> Then there's the ~/.guix-profile/share/dbus-1/services directory.
>
> ~/.guix-profile/share is one of the XDG_DATA_DIRS.
>
> dbus-specification.xml specifies that $XDG_DATA_DIRS/dbus-1/services is to be
> searched by the user bus.
>
> But this directory only contains files of packages that I personally installed
> into my profile - not of the dependencies.  In this case I didn't install the
> package of org.gtk.vfs.UDisks2VolumeMonitor - so the service file resides in
> /gnu/store/85ih21qjgqcicjkqkw5v96wjvh9hq9g3-gvfs-1.32.1/share/dbus-1/services/org.gtk.vfs.UDisks2VolumeMonitor.service
>  .
>
> I wonder why it works with the GNOME desktop.  Does it really?
>
> Possible workaround:
>
> youruser$ guix package -i gvfs
I've always had gvfs installed and it hasn't made any difference as far
as I can tell
>
> Possible fix:
>
> Make nautilus and other Guix packages using gvfs propagate gvfs.
>
> Possible different fix:
>
> Add profile hook which also automatically provides service files of 
> dependencies
> without installing the packages into the profile.  I'm not sure how useful 
> that it
> since dbus will prefer a running service to service files anyway (I think).  
> But
> at least we would notice a conflict.
> Also, is it able to statically determine what these dependencies are?

Previously there was no $DBUS_SESSION_BUS_ADDRESS. After I modified slim
to add dbus-launch, I have
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-Rc7AP3Xnzz,guid=97d26aba11773a9ce755829b5b611375

but it didn't fix the issue, and caused those weird errors. Actually I'm
not getting those errors anymore, maybe due to reconfiguring and
rebooting. When I run `dbus-launch bash` , it overwrites that value with
a new value in the current environment:
unix:abstract=/tmp/dbus-1vzMgxAURi,guid=98eb63bd2e22340a0c1d3bd85b6116d5
 and then running pcmanfm/evince only from that bash shell works fine,
running outside it or from dmenu doesn't.