How to prevent Avahi adding -2 to hostnames

Question

Often (maybe 80% of the time), when I reboot a machine running Avahi, it starts using machinename-2.local as it's hostname. All the machines on my network have unique hostnames, so there is no collision.

How do I prevent Avahi from appending -2 to hostnames?

(This turns out to be an incredibly difficult thing to Google for...)

Did you find a solution? In my case I have an apple macbook on the same network and two raspberry pis running with avahi-daemon and one of those RPis generates this conflict — ffleandro, Mar 24 '21 at 14:59
@ffleandro Just wanted to join on to that "Did you find a solution?" (I started getting the problem with a simple normal install of ubuntu 20.04 desktop, about a week after setting it up.) — Owen_AR, Apr 01 '21 at 17:05
I haven' found a solution yet. Do you have more than one avahi server in the same network? Found this ticket on the project, but it is still open. There is already a PR open but hasn't been merge: https://github.com/lathiat/avahi/issues/117 — ffleandro, Apr 02 '21 at 13:54

score 3 · Answer 1 · answered Dec 13 '14 at 01:26

3

This is also the case with OS X machines.

If the hostname is already in use on the network it bumps the counter to make the names unique again. I would suspect that the machine in question may have two netcards to the same network (cabled and wireless) or that you have a bonjour proxy running (which may be unknown to you) which helps sleeping machines by holding their hostname active. To be more certain you may want to describe your network better.

answered Dec 13 '14 at 01:26

Thorbjørn Ravn Andersen

1,354
8
14

Sorry for the slow reply. I certainly don't have two network cards in either of the machines that do this. How would I determine if I have a bonjour proxy anywhere? – dty Jan 20 '15 at 14:40
Do you own any Apple devices? – Thorbjørn Ravn Andersen Jun 11 '16 at 07:56
Several network devices work as bonjour proxies which can result in the same behavior – Thorbjørn Ravn Andersen Jun 13 '16 at 06:45
Hmm. I've only got one device that should be acting as a Bonjour Proxy (I now understand the relevance of this more than I did a year ago!) I have an Apple TV, but no desktop Mac, AirPort or Time Capsule. I do have iPhone, iPad, MacBook and an Apple Watch, but I don't think any of those should act as a Bonjour Proxy. – dty Jun 14 '16 at 16:12
AppleTV does, if it is alone on the network. – Thorbjørn Ravn Andersen Jun 14 '16 at 22:56

score 2 · Answer 2 · answered Nov 14 '18 at 18:44

In my case, this behavior is caused by a Plex Media Server inside a docker container which runs its own avahi-daemon. I'm using this docker image: https://hub.docker.com/r/linuxserver/plex/

The number was increased very often, without need to restart.

After stopping the docker container and a restart of avahi-daemon.service, the numbers disappeared.

Ken H · Answer 3 · 2021-12-13T22:11:23.047

I have the same problem on a Raspberry Pi. Until a better solution comes along, Ive added a crontab entry to run this script every day.

#!/bin/bash

writelog()
{
echo $(date) >> /home/pi/avahirestart.log
}
aname=$(avahi-resolve -a $(hostname -I|cut -d' ' -f1)|cut -f2)
if [[ "$aname" = *"-2"* ]];then
sudo service avahi-daemon restart
writelog
fi
if [[ "$aname" = *"-3"* ]];then
sudo service avahi-daemon restart
writelog
fi

score 0 · Answer 4 · answered Dec 31 '22 at 19:22

Here's an event-based dbus listener that looks for avahi hostname changes, and tries to remove the -2 suffix. It runs on startup as a systemd service (the gist includes an example service unitfile). I'm running it on a Debian server, although any distro that has dbus should be fine.

The benefit with this approach is that the script doesn't rely on polling, so when the hostname changes, it will quickly be changed back.

import dbus, avahi
from dbus.mainloop.glib import DBusGMainLoop
from gi.repository import GLib
import time

class Runner():
    def __init__(self, avahi_server):
        self.avahi_server = avahi_server

    def on_state_change(self, state, error):
        if state == avahi.SERVER_COLLISION:
            print(f"[state: collision] collided, waiting 5s...")
            time.sleep(5)

        elif state == avahi.SERVER_RUNNING:
            hostname = self.avahi_server.GetHostName()
            print(f"[state: running] hostname changed: {hostname}")
            if hostname.endswith("-2"):
                hostname = str(hostname)[0:-2]
                print(f"removing `-2` suffix: {hostname}")
                self.avahi_server.SetHostName(hostname)

def main():
    DBusGMainLoop(set_as_default=True)
    bus = dbus.SystemBus()
    object  = bus.get_object("org.freedesktop.Avahi","/")
    avahi_server = dbus.Interface(object, 'org.freedesktop.Avahi.Server')
    runner = Runner(avahi_server)
    avahi_server.connect_to_signal('StateChanged', runner.on_state_change)
    print("Starting main loop")
    loop = GLib.MainLoop()
    loop.run()

if __name__ == '__main__':
    main()

https://gist.github.com/dymk/d06425d932c96916f27eed9bfc5bb7cc

score 0 · Answer 5 · answered Jan 30 '23 at 21:45

See section 4.7 "Hostname changes with appending incrementing numbers" in Avahi. Here it states it is a known bug in Avahi. One workaround is to turn off IPv6 on your local router. I tried and it worked in my network. I have struggled with a Raspberry pi 4 for some time. I don't know why I haven't seen the issue on other Pis.

How to prevent Avahi adding -2 to hostnames

5 Answers5