No unicast resolution if avahi is started before network is configured

[jwelsh]

If avahi-daemon starts before /etc/resolv.conf is configured by dhcp, it will not resolve any requests via unicast DNS (e.g. for wide-area DNS-SD). If I do avahi-daemon -r it will reload resolv.conf (via the chroot helper I assume) and succeed. Perhaps resolv.conf could be added to the inotify watch list?

I'm using gentoo and avahi-daemon is usually started before DHCP is acquired. On Debian it seems ok normally but I can reproduce by ifdown / restart avahi / ifup.

I'd imagine this is a worse problem for laptops using networkmanager or some such.

[lennart]

It's a bit hard to do that, since we'd have to watch all of /etc and Avahi itself is chrooted to /etc/avahi. Not sure if it would be worth making this possible.

[jwelsh]

My impression was that inotify allowed watching of individual files, but if not, then indeed that's not very clean.

But, doesn't avahi detect changes in network interfaces/addresses? i.e. it reports "Joining mDNS multicast group on interface eth0.IPv4 with address xxxx" when that interface comes up. Would that be a suitable trigger for reloading? Perhaps only if there were no nameservers before.

[lennart]

Usually the network interface is brought up before resolv.conf is changed, such a logic would hence be race.

If we wanted to use inotify we'd have to watch /etc itself, since resolv.conf is usually not rewritten, but moved away and created anew. This is not really scalable and ugly too.

I think the best way is to change software that rewrites resolv.conf to send a SIGHUP to avahi-daemon. Or use a local DNS cache such as dnsmasq.