[Pkg-utopia-maintainers] Bug#846381: avahi-daemon: cups frequently forgets about all printers untils restarting avahi-daemon

[Brian Potkin]

On Mon 01 Jan 2018 at 13:44:15 +0100, Helmut Grohne wrote:

> Control: tags -1 - moreinfo
> 
> On Mon, Jan 01, 2018 at 12:46:47AM +0000, Brian Potkin wrote:
> > Thanks you for your report, Helmut.
> 
> Thanks for looking into this.
> 
> > On Wed 30 Nov 2016 at 20:57:01 +0100, Helmut Grohne wrote:
> > > Since Debian jessie, cups uses avahi to broadcast its printers to the
> > > local network. I have a jessie cups with a few printers and publish them
> > > via avahi. Now I am seeing a little weird behaviour on client systems:
> > > After booting their cups daemons know about the broadcasted printers,
> > > but after some time (usually a few times a day) they forget. I have no
> > 
> > What are the symptoms?  How do you know that the printing system does
> > not see the remote broadcasted printers on the clients?
> 
> When printers are broadcasted, client cups systems create
> /etc/cups/ppd/<something>.ppd for each remote printer. These files exist
> after booting and then vanish. Another way to diagnose the presence of

cups-browsed creates the PPDs.

> the issue is running "lpstat -a". After boot, it lists all the printers,
> but after a while, the output becomes "lpstat: No destinations added."

lpstat gets remote printer information from cups-browsed.

> When I try to print something (e.g. using evince), I am presented with
> an empty printer list. Then I restart avahi-daemon on the client system
> and the files are back and "lpstat -a" gives a printer list again until
> it forgets again.

evince can get remote printer information from cups-browsed but, if the
latter is not running, it browses the Bonjour broadcasts of servers and
printers directly, just as avahi-browse does.

> > First things first. Are you still experiencing this behaviour on an
> > up-to-date unstable/testing system?
> 
> Yes. I see this behaviour on stretch and sid.

I am working with sid. Are you using AppArmor on Stretch?

Let's see whether cups-browsed has any connection with the issue. Stop
it running and bring up evince. Its print dialog should show the remote
printers it gets from mdns broadcasts. You relate the printers disappear
a few times a day, so we shouldn't have to wait too long to see whether
it happens in this situation. BTW, is there any discernable pattern to
the behaviour? Time of day, time interval etc?

> Is there anything else I can check? Maybe trace something? Turn on some
> debug logging somewhere? The issue is sufficiently annoying that I am
> willing to put some time into it.

Thanks for the offer. Have a good look at what journalctl says. Search
for clues with "avahi", "audit", SIGTERM (and anything else you can
think of).

Cheers,

Brian.