Avahi isn't being used to resolve .local domain names

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1

Hello, I’m new to Fedora (but not to Linux in general) and in general I like it a lot. This one problem has me stumped though. mDNS name hostname resolution isn’t working. Avahi is able to resolve the hostname when I use avahi-resolve-host-name, but getent hosts doesn’t resolve it. For example, with an mDNS-enabled printer:

[mtrescott@R8501300 ~]$ avahi-resolve-host-name xpress-c1860fw.local
xpress-c1860fw.local    192.168.1.64
[mtrescott@R8501300 ~]$ getent hosts xpress-c1860fw.local
[mtrescott@R8501300 ~]$ echo $?
2

I’m not sure what’s wrong here since Avahi seems to be working fine on its own. Here’s what I’ve tried:

  • Checking firewall configuration: mDNS is allowed (and anyway, Avahi works on its own)
  • Adding 127.0.0.1 to NetworkManager’s additional DNS servers for my connection config. (this adds a nameserver 127.0.0.1 line to /etc/resolv.conf.
  • Adding an /etc/mdns.allow file with the default settings to allow .local domains.
  • Switching Avahi to use .alocal instead of .local in /etc/avahi/avahi-daemon.conf in case the router’s DNS server handles the .local TLD already.

I don’t think my configuration is out of the ordinary anywhere else. I installed Fedora using the minimal install media and then gradually installed the packages that I want/need. Here’s some configuration lines that might be relevent:

hosts line from /etc/nsswitch.conf:
hosts: files mdns4_minimal [NOTFOUND=return] dns myhostname

Contents of /etc/resolv.conf:

# Generated by NetworkManager
search attlocal.net
nameserver 192.168.1.254
nameserver 127.0.0.1
nameserver 2600:1702:5a0:82f0::1

If anyone can help me on this, thank you in advance!

2

Just for your information. I don’t have avahi installed, but executing getent hosts xpress-c1860fw.local followed by echo $? returns the same number 2. However, if I do the same for a host I know exists, i get the entries for that host from getent.

Are you sure it is not just a problem with the xpress host?

P.S. I may be a longtime fedora user, but I never used avahi and I am certainly not server knowledgeable. Hope you can forgive if this is a newby query xD.

3

Yeah, I’m sure it must be something wrong with my Fedora configuration because when I use getent hosts the resolution should be routed through Avahi via the mdns4_minimal NSSwitch module.

4

If your had started with the minimal install media, maybe then your setup is having a systemd-resolved running instead of the avahi-daemon.service?

Arch Wiki:
"
Note: systemd-resolved has a built-in multicast DNS service, make sure to disable systemd-resolved’s mDNS resolver and responder or disable systemd-resolved.service entirely before using Avahi. For details, refer to resolved.conf(5).
"

5

Oh yeah, I forgot to mention that I checked that too—thanks for the suggestion though. systemd-resolved isn’t running:

● systemd-resolved.service - Network Name Resolution
   Loaded: loaded (/usr/lib/systemd/system/systemd-resolved.service; disabled; vendor preset: disabled)
   Active: inactive (dead)
     Docs: man:systemd-resolved.service(8)
           https://www.freedesktop.org/wiki/Software/systemd/resolved
           https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
           https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
6

man avahi-daemon:
"
If you enable publish-resolv-conf-dns-servers in avahi-daemon.conf the file /etc/resolv.conf will be read, too.
"
?

PS:
https://fedoramagazine.org/find-systems-easily-lan-mdns/

:flying_saucer: !? SELinux? Are your have a “Permission denied” entries inside of the system logs?
“https://discussion.fedoraproject.org/t/cannot-connect-to-openvpn-using-gnome/76347”

7

I tried uncommenting publish-resolv-conf-dns-servers=yes in avahi-daemon.conf and restarting Avahi, but it didn’t change anything. And there aren’t any relevant errors when I do journalctl --boot | grep denied

I wish I know how to debug something like this with GDB or something.

8

If i’m understand correct, your will need an debug build of the program your wish to debug. With the symbols and the such not stripped (not dev myself).

PS: Maybe your try to (i’ve limited traffic myself) install the Workstation variant? :flying_saucer: Of course, your potentially will have less fun…

9

By trial and error, I finally figured it out! (Kinda—I have no idea why this works and the default config doesn’t)

I created the file /etc/mdns.allow with the following contents:

.local
.local.

(I added a trailing empty line to this file but it didn’t make any difference in my tests.)

Then I switched to using the regular mdns4 or mdns module instead of mdns4_minimal in /etc/nsswitch.conf, and it worked! Apparently this was a combination I didn’t try before.

My hosts line now looks like:

hosts:      files mdns4 [NOTFOUND=return] dns myhostname

And I get the output I expect for the network printer:

$ getent hosts xpress-c1860fw.local
192.168.1.64    xpress-c1860fw.local

Side note 1: What helped me figure this out was the --service parameter for the getent command. By using getent --service=mdns hosts xpress-c1860fw I was able to bypass the sequence of services specified in /etc/nsswitch.conf and isolate the problem to the mdns4_minimal NSS service. The red flag was the fact that getent would return immediately, so I know that there was no network activity going on. Apparently mdns4_minimal is broken.

Side note 2: I really don’t understand why mdns4_minimal doesn’t work. It ought to. Maybe this deserves a bug report?

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