Difference between revisions of "Avahi"

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[[Category:Networking]]
+
[[Category:Multicast DNS]]
 
[[fr:Avahi]]
 
[[fr:Avahi]]
 
[[ja:Avahi]]
 
[[ja:Avahi]]
 
From [[Wikipedia:Avahi (software)]]:
 
From [[Wikipedia:Avahi (software)]]:
:''"[http://avahi.org/ Avahi] is a free [[Wikipedia:Zero-configuration networking|Zero-configuration networking]] (zeroconf) implementation, including a system for multicast DNS/DNS-SD service discovery. It allows programs to publish and discover services and hosts running on a local network with no specific configuration. For example you can plug into a network and instantly find printers to print to, files to look at and people to talk to. It is licensed under the GNU Lesser General Public License (LGPL)."''
+
:[http://avahi.org/ Avahi] is a free [[Wikipedia:Zero-configuration networking|Zero-configuration networking]] (zeroconf) implementation, including a system for multicast DNS/DNS-SD service discovery. It allows programs to publish and discover services and hosts running on a local network with no specific configuration. For example you can plug into a network and instantly find printers to print to, files to look at and people to talk to. It is licensed under the GNU Lesser General Public License (LGPL).
  
 
== Installation ==
 
== Installation ==
[[pacman|Install]] {{Pkg|avahi}} from the [[official repositories]].
+
 
 +
[[Install]] the {{Pkg|avahi}} package.
  
 
You can manage the Avahi daemon with {{ic|avahi-daemon.service}} [[systemd#Using units|using systemd]].
 
You can manage the Avahi daemon with {{ic|avahi-daemon.service}} [[systemd#Using units|using systemd]].
  
=== Enable IPv6 ===
+
{{Note|[[systemd-resolved]] has a built-in multicast DNS service, make sure to disable systemd-resolved's mDNS resolver and responder or [[disable]] {{ic|systemd-resolved.service}} entirely before using Avahi. For details, refer to {{man|5|resolved.conf}}.}}
For some reason, Avahi comes with IPv6 disabled by default. To enable it, set {{ic|use-ipv6}} to {{ic|yes}} in {{ic|/etc/avahi/avahi-daemon.conf}}.
 
  
 
== Using Avahi ==
 
== Using Avahi ==
 +
 +
=== Hostname resolution ===
 +
 +
Avahi provides local hostname resolution using a "''hostname''.local" naming scheme. To enable it, install the {{Pkg|nss-mdns}} package and [[start]] {{ic|avahi-daemon.service}}.
 +
 +
Then, edit the file {{ic|/etc/nsswitch.conf}} and change the {{ic|hosts}} line to include {{ic|1=mdns_minimal [NOTFOUND=return]}} before {{ic|resolve}} and {{ic|dns}}:
 +
 +
hosts: ... '''mdns_minimal [NOTFOUND=return]''' resolve [!UNAVAIL=return] dns ...
 +
 +
{{Note|If you experience slowdowns in resolving {{ic|.local}} hosts try to use {{ic|mdns4_minimal}} instead of {{ic|mdns_minimal}}.}}
 +
 +
==== Configuring mDNS for custom TLD ====
 +
 +
The {{ic|mdns_minimal}} module handles queries for the {{ic|.local}} TLD only. Note the {{ic|<nowiki>[NOTFOUND=return]</nowiki>}}, which specifies that if {{ic|mdns_minimal}} cannot find {{ic|*.local}}, it will not continue to search for it in {{ic|dns}}, {{ic|myhostname}}, etc.
 +
 +
In case you want Avahi to support other TLDs, you should:
 +
 +
* replace {{ic|1=mdns_minimal [NOTFOUND=return]}} with the full {{ic|mdns}} module. There also are IPv4-only and IPv6-only modules {{ic|mdns[46](_minimal)}}
 +
* customize {{ic|/etc/avahi/avahi-daemon.conf}} with the {{ic|domain-name}} of your choice
 +
* whitelist Avahi custom TLDs in {{ic|/etc/mdns.allow}}
 +
 +
==== Tools ====
 +
 +
Avahi includes several utilities which help you discover the services running on a network. For example, run
 +
 +
$ avahi-browse --all --ignore-local --resolve --terminate
 +
 +
to discover services in your network.
 +
 +
The Avahi Zeroconf Browser ({{ic|avahi-discover}} – note that it needs avahi's optional dependencies {{Pkg|gtk3}}, {{Pkg|python-dbus}} and {{Pkg|python-gobject}}) shows the various services on your network. You can also browse SSH and VNC Servers using {{ic|bssh}} and {{ic|bvnc}} respectively.
 +
 +
=== Firewall ===
 +
 +
Be sure to open UDP port {{ic|5353}} if you're using a [[firewall]].
 +
 +
=== Link-Local (Bonjour/Zeroconf) chat ===
 +
 +
Avahi can be used for bonjour protocol support under linux. Check [[Wikipedia:Comparison of instant messaging clients]] or [[List of applications#Instant messaging clients]] for a list of clients supporting the bonjour protocol.
 +
 
=== Obtaining IPv4LL IP address ===
 
=== Obtaining IPv4LL IP address ===
  
Line 26: Line 65:
  
 
Alternatively, run {{ic|avahi-autoipd}}:
 
Alternatively, run {{ic|avahi-autoipd}}:
 +
 
  # avahi-autoipd -D
 
  # avahi-autoipd -D
  
=== Hostname resolution ===
+
== Adding services ==
{{Note|Using Avahi for IPv6 hostname resolution is severly limited and not really usable.[https://blogs.gentoo.org/eva/2010/12/17/things-you-didnt-known-about-ipv6-link-local-address/] (summary: you '''cannot''' do something trivial as {{ic|ping6 archy.local}})}}
+
 
 +
Avahi advertises the services whose {{ic|*.service}} files are found in {{ic|/etc/avahi/services}}. Files in this directory must be readable by the {{ic|avahi}} user/group.
 +
 
 +
If you want to advertise a service for which there is no {{ic|*.service}} file, it is very easy to create your own.
 +
As an example, let's say you wanted to advertise a quote of the day (QOTD) service operating per RFC 865 on TCP port {{ic|17}} which you are running on your machine
 +
 
 +
The first thing to do is to determine the {{ic|<type>}}. {{man|5|avahi.service}} indicates that the type should be "the DNS-SD service type for this service. e.g. '_http._tcp'". Since the [http://www.dns-sd.org/ServiceTypes.html DNS-SD register was merged into the IANA register in 2010], we look for the service name on the [http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml IANA register] or in {{ic|/etc/services}} file. The service name shown there is {{ic|qotd}}. Since we're running QOTD on tcp, we now know the service is {{ic|_qotd._tcp}} and the port (per IANA and RFC 865) is {{ic|17}}.
 +
 
 +
Our service file is thus:
 +
 
 +
{{hc|qotd.service|<nowiki>
 +
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
 +
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
 +
 
 +
<service-group>
 +
 
 +
  <name replace-wildcards="yes">%h</name>
 +
 
 +
  <service>
 +
    <type>_qotd._tcp</type>
 +
    <port>17</port>
 +
  </service>
 +
 
 +
</service-group>
 +
</nowiki>}}
  
Avahi also allows you to access computers using their hostnames. However by default, {{ic|.local}} querying is disabled in Arch Linux. ''To enable support for .local'', edit the file {{ic|/etc/nsswitch.conf}} and change the line:
+
For more complicated scenarios, such as advertising services running on a different server, DNS sub-types and so on, consult {{man|5|avahi.service}}.
hosts: files dns myhostname
 
to:
 
hosts: files mdns_minimal [NOTFOUND=return] dns myhostname
 
  
For each host, install the {{Pkg|nss-mdns}} package and start {{ic|avahi-daemon.service}}.
+
=== SSH ===
==== Additional info about mdns ====
 
  
The {{ic|mdns_minimal}} module handles queries for the {{ic|.local}} TLD only. Note the {{ic|<nowiki>[NOTFOUND=return]</nowiki>}}, which specifies that if {{ic|mdns_minimal}} cannot find {{ic|*.local}}, it will not continue to search for it in {{ic|dns}}, {{ic|myhostname}}, etc. In case you have configured Avahi to use a different TLD, you should replace {{ic|1=mdns_minimal [NOTFOUND=return]}} with the full {{ic|mdns}} module. There also are IPv4-only and IPv6-only modules {{ic|mdns[46](_minimal)}}.
+
Avahi comes with an example service file to advertise a SSH server. To enable it:
  
==== Tools ====
+
# cp /usr/share/doc/avahi/ssh.service /etc/avahi/services/
  
Avahi includes several utilities which help you discover the services running on a network. For example, run
+
=== File sharing ===
avahi-browse -alr
 
to discover services in your network.
 
  
The Avahi Zeroconf Browser ({{ic|avahi-discover}} – note that it needs avahi's optional dependencies {{Pkg|pygtk}} and {{Pkg|python2-dbus}}) shows the various services on your network. You can also browse SSH and VNC Servers using {{ic|bssh}} and {{ic|bvnc}} respectively.
+
==== NFS ====
  
There's a good list of software with Avahi support at their website: http://avahi.org/wiki/Avah4users
+
If you have an [[NFS]] share set up, you can use Avahi to be able to automount them in Zeroconf-enabled browsers (such as Konqueror on KDE and Finder on macOS) or file managers such as [[GNOME/Files]].
  
===File sharing===
+
Create a {{ic|.service}} file in {{ic|/etc/avahi/services}} with the following contents:
  
====NFS====
 
If you have an [[NFS]] share set up, you can use Avahi to be able to automount them in Zeroconf-enabled browsers (such as Konqueror on KDE and Finder on OS X). Create a {{ic|.service}} file in {{ic|/etc/avahi/services}} with the following contents:
 
 
{{hc|/etc/avahi/services/nfs_Zephyrus_Music.service|<nowiki>
 
{{hc|/etc/avahi/services/nfs_Zephyrus_Music.service|<nowiki>
 
<?xml version="1.0" standalone='no'?>
 
<?xml version="1.0" standalone='no'?>
Line 65: Line 121:
 
     <txt-record>path=/data/shared/Music</txt-record>
 
     <txt-record>path=/data/shared/Music</txt-record>
 
   </service>
 
   </service>
</service-group></nowiki>}}
+
</service-group>
 +
</nowiki>}}
 +
 
 +
The port is correct if you have ''insecure'' as an option in your {{ic|/etc/exports}}; otherwise, it needs to be changed (note that ''insecure'' is needed for macOS clients). The path is the path to your export, or a subdirectory of it. For some reason the automount functionality has been removed from Leopard, however [http://www.macosxhints.com/article.php?story=20071116042238744 a script is available]. This was based upon [http://ubuntuforums.org/showthread.php?p=4387032#post4387032 this post].
  
The port is correct if you have ''insecure'' as an option in your {{ic|/etc/exports}}; otherwise, it needs to be changed (note that ''insecure'' is needed for OS X clients). The path is the path to your export, or a subdirectory of it. For some reason the automount functionality has been removed from Leopard, however [http://www.macosxhints.com/article.php?story=20071116042238744 a script is available]. This was based upon [http://ubuntuforums.org/showthread.php?p=4387032#post4387032 this post].
+
==== Samba ====
  
====Samba====
+
With the Avahi daemon running on both the server and client, the file manager on the client should automatically find the server.
Should work out-of-the-box.
 
  
====GShare====
+
==== Vsftpd ====
You can grab {{AUR|gshare}} from the [[Arch User Repository]] and have shared files between the LAN, with no configuration, no hours in samba hacking, no nothing - it just works.
 
  
====Vsftpd====
+
You can also auto-discover regular FTP servers, such as [[vsftpd]]. Install the {{Pkg|vsftpd}} package and change the settings of vsftpd according to your own personal preferences (see [http://ubuntuforums.org/showthread.php?t=218630 this thread on ubuntuforums.org] or {{man|5|vsftpd.conf}}).
Sourced from [http://ubuntuforums.org/showthread.php?t=218630 ubuntuforums.org].
 
If you would rather use a regular ftp service, install vsftpd and avahi. Change the settings of vsftpd according to what is shown on the ubuntuforums page or according to your own personal preferences (See 'man vsftpd.conf).
 
  
Create a ftp.service file in /etc/avahi/services and paste in that file
+
Create a {{ic|.service}} file in {{ic|/etc/avahi/services}} with the following contents:
<?xml version="1.0" standalone='no'?>
+
 
    <!DOCTYPE service-group SYSTEM "avahi-service.dtd">
+
{{hc|/etc/avahi/services/ftp.service|<nowiki>
    <service-group>
+
<?xml version="1.0" standalone='no'?>
    <name>FTP file sharing</name>
+
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
    <service>
+
<service-group>
 +
  <name>FTP file sharing</name>
 +
  <service>
 
     <type>_ftp._tcp</type>
 
     <type>_ftp._tcp</type>
 
     <port>21</port>
 
     <port>21</port>
    </service>
+
  </service>
    </service-group>
+
</service-group>
When you are done, [[restart]] the {{ic|avahi-daemon.service}} and {{ic|vsftpd.service}} services.
+
</nowiki>}}
 
 
After that you should be able to browse through the ftp server from another computer in your network. The steps shown in this section are created so that the ftp server is 'advertised' by avahi to the local Zeroconf network.
 
 
 
Unless you are using GNOME or KDE, you might not be able to log in to the ftp server directly through your file manager, and so you will have to use a ftp client pointed to the IP address of the server or the hostname of the machine (as shown in [[#Hostname_resolution|this section]]).
 
 
 
====Giver====
 
[http://code.google.com/p/giver/ Giver] is a mono program that allows simple file-sharing between two desktops when both are running Giver. All you need to do is click and drag the file to the name or picture of the person you wish to send the file to.
 
 
 
A package is on the {{AUR|giver}}.
 
  
Note that this depends on gnome-sharp, which has heavy GNOME dependencies.
+
The FTP server should now be advertised by Avahi. You should now be able to find the FTP server from a file manager on another computer in your network. You might need to enable [[#Hostname resolution]] on the client.
  
===Link-Local (Bonjour/Zeroconf) chat===
+
=== AirPrint from Mobile Devices ===
  
Avahi can be used for bonjour protocol support under linux. Check [[Wikipedia:Comparison of instant messaging clients]] or [[List of applications#Instant messaging]] for a list of clients supporting the bonjour protocol.
+
{{Merge | AirPort#Printing | AirPrint is a feature provided by the Apple AirPort Express and by some printers. The manual configuration technique (using JetDirect) can also apply here and may be easier.}}
  
===Airprint from Mobile Devices===
+
Avahi along with [[CUPS]] also provides the capability to print to just about any printer from airprint compatible mobile devices. In order to enable print capability from your device, simply create an Avahi service file for your printer in {{ic|/etc/avahi/services/}}. An example of a generic services file for an HP-Laserjet printer would be similar to the following with the {{ic|name}}, {{ic|rp}}, {{ic|ty}}, {{ic|adminurl}} and {{ic|note}} fields changed.
Avahi along with CUPS also provides the capability to print to just about any printer from airprint compatible mobile devices. In order to enable print capability from your device, simply create an avahi service file for your printer in /etc/avahi/services and restart avahi. An example of a generic services file for an HP-Laserjet printer would be similar to the following with the name, rp, ty, adminurl and note fields changed. Save the file as /etc/avahi/services/youFileName.service:
 
  
{{bc|<nowiki>
+
{{hc|/etc/avahi/services/airprint.service|<nowiki>
 
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
 
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
 
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
 
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
Line 146: Line 193:
 
</nowiki>}}
 
</nowiki>}}
  
Alternatively, https://raw.github.com/tjfontaine/airprint-generate/master/airprint-generate.py can be used to generate Avahi service files. It depends on python2 and pycups. The script can be run using:
+
Alternatively, https://raw.github.com/tjfontaine/airprint-generate/master/airprint-generate.py can be used to generate Avahi service files. It depends on {{Pkg|python2}} and {{AUR|python2-pycups}}. The script can be run using:
  
 
  # python2 airprint-generate.py -d /etc/avahi/services
 
  # python2 airprint-generate.py -d /etc/avahi/services
Line 152: Line 199:
 
{{Note|If your printer under http://localhost:631/printers is "Not Shared", this python script won't output any file to /etc/avahi/services; in that case, you'll need to "Modify Printer" under one of the CUPS drop-down menus to turn sharing on.  If that doesn't work, check out the ArchWiki on [[CUPS printer sharing]].}}
 
{{Note|If your printer under http://localhost:631/printers is "Not Shared", this python script won't output any file to /etc/avahi/services; in that case, you'll need to "Modify Printer" under one of the CUPS drop-down menus to turn sharing on.  If that doesn't work, check out the ArchWiki on [[CUPS printer sharing]].}}
  
=== Firewall ===
+
== Troubleshooting ==
 
 
Be sure to open UDP port 5353 if you're using iptables:
 
  # iptables -A INPUT -p udp -m udp --dport 5353 -j ACCEPT
 
 
 
If you're following the more-than-useful [[Simple stateful firewall]] format for your firewall:
 
  # iptables -A UDP -p udp -m udp --dport 5353 -j ACCEPT
 
 
 
=== Customizing Avahi ===
 
==== Adding Services ====
 
 
 
Avahi advertises the services whose {{ic|*.service}} files are found in {{ic|/etc/avahi/services}}. If you want to advertise a service for which there is no {{ic|*.service}} file, it is very easy to create your own.
 
 
 
As an example, let's say you wanted to advertise a quote of the day (QOTD) service operating per [http://tools.ietf.org/html/rfc865 RFC865] on TCP port 17 which you are running on your machine
 
 
 
The first thing to do is to determine the {{ic|<type>}}. {{ic|man avahi.service}} indicates that the
 
type should be "the DNS-SD service type for this service. e.g. '_http._tcp'". Since the [http://www.dns-sd.org/ServiceTypes.html DNS-SD register was merged into the IANA register in 2010], we look for the service name on the [http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml IANA register] or in {{ic|/etc/services}} file. The service name shown there is {{ic|qotd}}. Since we're running QOTD on tcp, we now know the service is {{ic|_qotd._tcp}} and the port (per IANA and RFC865) is 17.
 
 
 
Our {{ic|qotd.service}} file is thus:
 
 
 
{{bc|<nowiki>
 
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
 
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
 
 
 
<!--
 
  This file is part of avahi.
 
 
 
  avahi is free software; you can redistribute it and/or modify it
 
  under the terms of the GNU Lesser General Public License as
 
  published by the Free Software Foundation; either version 2 of the
 
  License, or (at your option) any later version.
 
 
 
  avahi is distributed in the hope that it will be useful, but
 
  WITHOUT ANY WARRANTY; without even the implied warranty of
 
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 
  General Public License for more details.
 
 
 
  You should have received a copy of the GNU Lesser General Public
 
  License along with avahi; if not, write to the Free Software
 
  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
 
  02111-1307 USA.
 
-->
 
 
 
<!-- See avahi.service(5) for more information about this configuration file -->
 
 
 
<service-group>
 
 
 
  <name replace-wildcards="yes">%h</name>
 
 
 
  <service>
 
    <type>_qotd._tcp</type>
 
    <port>17</port>
 
  </service>
 
 
 
</service-group>
 
</nowiki>}}
 
 
 
For more complicated scenarios, such as advertising services running on a different server, DNS sub-types and so on, consult {{ic|man avahi.service}}.
 
 
 
==== Modifying the service-types database ====
 
As noted above, avahi comes with tools to browse advertised services. Both {{ic|avahi-browse}} and {{ic|avahi-discover}} use a database file to furnish descriptions of the relevant service. That database contains the names of many, but not all, services.
 
 
 
Sadly, it doesn't contain the QOTD service we just created. Thus {{ic|avahi-browse -a}} would show the following ugly entry
 
 
 
+ wlp2s0 IPv4 MyServer                                        _qotd._tcp local
 
 
 
===== Getting the Sources =====
 
 
 
First, download the files {{ic|build-db.in}} and {{ic|service-types}} files from the {{ic|service-type-database}} subdirectory in the [https://github.com/Distrotech/avahi the avahi github mirror] to a build directory.
 
 
 
wget https://raw.githubusercontent.com/Distrotech/avahi/distrotech-avahi/service-type-database/build-db.in
 
wget https://raw.githubusercontent.com/Distrotech/avahi/distrotech-avahi/service-type-database/service-types
 
 
 
===== Modify the Sources =====
 
 
 
Second, create the following script:
 
 
 
#!/bin/bash
 
sed -e 's,@PYTHON\@,/usr/bin/python2.7,g' \
 
    -e 's,@DBM\@,gdbm,g' < build-db.in > build-db
 
chmod +x build-db
 
 
 
This mimics what the Makefile would do if one were building all of avahi. It creates a file named build-b.
 
 
 
$./whatever_you_named_the_script.sh
 
$ ls
 
build-db build-db.in service-types whatever_you_named_the_script.sh
 
 
 
Third, make the changes needed to add your new QOTD service to the {{ic|service-types}} file. This file has one entry per line, with the entries in the format {{ic|type:Human Readable Description}}. Note that the human readable description can contain spaces.
 
 
 
In our example, we add the following entry to the end of the file:
 
 
 
_qotd._tcp:Quote of the Day (QOTD) Server
 
 
 
===== Build and Install the New Database =====
 
 
 
Now run the {{ic|build-db}} python script (be sure to use python2 not python3). This will build the {{ic|service-types.db}} file. Check to make sure it's been built and use {{ic|gdbmtools}} to make sure the new database is loadable and contains the new entry:
 
 
 
$/usr/bin/python2.7 build-db
 
$ls
 
build-db build-db.in service-types service-types.db whatever_you_named_the_script.sh
 
$gdbmtool service-types.db
 
 
Welcome to the gdbm tool.  Type ? for help.
 
 
gdbmtool>fetch _qotd._tcp
 
Quote of the Day (QOTD) Server
 
gdbmtool>quit
 
 
 
Now copy the old database to a backup location, move the new database to the live directory and use {{ic|avahi-browse}} database dump command to make sure avahi sees the new entry:
 
  
$cp /usr/lib/avahi/service-types.db /backup-directory
+
=== Hostname changes with appending incrementing numbers ===
$sudo cp /build-directory/service-types.db /usr/lib/avahi/service-types.db
 
$avahi-browse -b | grep QOTD
 
Quote of the Day (QOTD) Server
 
  
The entry in {{ic|avahi-browse}} should now be:
+
This is a [https://github.com/lathiat/avahi/issues/117 known bug] that is caused by a hostname race condition. One possible workaround is [https://github.com/lathiat/avahi/issues/117#issuecomment-302849130 disabling IPv6] to attempt to prevent the race condition. If multiple interfaces are present [https://github.com/lathiat/avahi/issues/117#issuecomment-401225716 use allow-interfaces] to limit Avahi to a single interface. Another possible workaround is to [https://github.com/lathiat/avahi/issues/117#issuecomment-442201162 disable the cache] to prevent Avahi from checking for host name conflicts altogether, but this prevents Avahi from performing lookups.
  
+ wlp2s0 IPv4 MyServer                                        Quote of the Day (QOTD) Server local
+
== See also ==
  
==See also==
 
 
* [http://avahi.org/ Avahi] - Official project website
 
* [http://avahi.org/ Avahi] - Official project website
* [http://en.wikipedia.org/wiki/Avahi_%28software%29 Wikipedia entry]
+
* [[Wikipedia:Avahi (software)]]
* [http://www.apple.com/support/downloads/bonjourforwindows.html Bonjour for Windows] - Enable Zeroconf on Windows
+
* [https://www.apple.com/itunes/download/ iTunes (includes Bonjour)] - Enable Zeroconf on Windows
 
* http://www.zeroconf.org/
 
* http://www.zeroconf.org/

Latest revision as of 08:25, 16 February 2020

From Wikipedia:Avahi (software):

Avahi is a free Zero-configuration networking (zeroconf) implementation, including a system for multicast DNS/DNS-SD service discovery. It allows programs to publish and discover services and hosts running on a local network with no specific configuration. For example you can plug into a network and instantly find printers to print to, files to look at and people to talk to. It is licensed under the GNU Lesser General Public License (LGPL).

Installation

Install the avahi package.

You can manage the Avahi daemon with avahi-daemon.service using systemd.

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).

Using Avahi

Hostname resolution

Avahi provides local hostname resolution using a "hostname.local" naming scheme. To enable it, install the nss-mdns package and start avahi-daemon.service.

Then, edit the file /etc/nsswitch.conf and change the hosts line to include mdns_minimal [NOTFOUND=return] before resolve and dns:

hosts: ... mdns_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns ...
Note: If you experience slowdowns in resolving .local hosts try to use mdns4_minimal instead of mdns_minimal.

Configuring mDNS for custom TLD

The mdns_minimal module handles queries for the .local TLD only. Note the [NOTFOUND=return], which specifies that if mdns_minimal cannot find *.local, it will not continue to search for it in dns, myhostname, etc.

In case you want Avahi to support other TLDs, you should:

  • replace mdns_minimal [NOTFOUND=return] with the full mdns module. There also are IPv4-only and IPv6-only modules mdns[46](_minimal)
  • customize /etc/avahi/avahi-daemon.conf with the domain-name of your choice
  • whitelist Avahi custom TLDs in /etc/mdns.allow

Tools

Avahi includes several utilities which help you discover the services running on a network. For example, run

$ avahi-browse --all --ignore-local --resolve --terminate

to discover services in your network.

The Avahi Zeroconf Browser (avahi-discover – note that it needs avahi's optional dependencies gtk3, python-dbus and python-gobject) shows the various services on your network. You can also browse SSH and VNC Servers using bssh and bvnc respectively.

Firewall

Be sure to open UDP port 5353 if you're using a firewall.

Link-Local (Bonjour/Zeroconf) chat

Avahi can be used for bonjour protocol support under linux. Check Wikipedia:Comparison of instant messaging clients or List of applications#Instant messaging clients for a list of clients supporting the bonjour protocol.

Obtaining IPv4LL IP address

Merge-arrows-2.pngThis article or section is a candidate for merging with dhcpcd.Merge-arrows-2.png

Notes: should be merged into the main page (Discuss in Talk:Avahi#)

By default, if you are getting IP using DHCP, you are using the dhcpcd package. It can attempt to obtain an IPv4LL address if it failed to get one via DHCP. By default this option is disabled. To enable it, comment noipv4ll string:

/etc/dhcpcd.conf
...
#noipv4ll
...

Alternatively, run avahi-autoipd:

# avahi-autoipd -D

Adding services

Avahi advertises the services whose *.service files are found in /etc/avahi/services. Files in this directory must be readable by the avahi user/group.

If you want to advertise a service for which there is no *.service file, it is very easy to create your own. As an example, let's say you wanted to advertise a quote of the day (QOTD) service operating per RFC 865 on TCP port 17 which you are running on your machine

The first thing to do is to determine the <type>. avahi.service(5) indicates that the type should be "the DNS-SD service type for this service. e.g. '_http._tcp'". Since the DNS-SD register was merged into the IANA register in 2010, we look for the service name on the IANA register or in /etc/services file. The service name shown there is qotd. Since we're running QOTD on tcp, we now know the service is _qotd._tcp and the port (per IANA and RFC 865) is 17.

Our service file is thus:

qotd.service
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">

<service-group>

  <name replace-wildcards="yes">%h</name>

  <service>
    <type>_qotd._tcp</type>
    <port>17</port>
  </service>

</service-group>

For more complicated scenarios, such as advertising services running on a different server, DNS sub-types and so on, consult avahi.service(5).

SSH

Avahi comes with an example service file to advertise a SSH server. To enable it:

# cp /usr/share/doc/avahi/ssh.service /etc/avahi/services/

File sharing

NFS

If you have an NFS share set up, you can use Avahi to be able to automount them in Zeroconf-enabled browsers (such as Konqueror on KDE and Finder on macOS) or file managers such as GNOME/Files.

Create a .service file in /etc/avahi/services with the following contents:

/etc/avahi/services/nfs_Zephyrus_Music.service
<?xml version="1.0" standalone='no'?>
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service-group>
  <name replace-wildcards="yes">NFS Music Share on %h</name>
  <service>
    <type>_nfs._tcp</type>
    <port>2049</port>
    <txt-record>path=/data/shared/Music</txt-record>
  </service>
</service-group>

The port is correct if you have insecure as an option in your /etc/exports; otherwise, it needs to be changed (note that insecure is needed for macOS clients). The path is the path to your export, or a subdirectory of it. For some reason the automount functionality has been removed from Leopard, however a script is available. This was based upon this post.

Samba

With the Avahi daemon running on both the server and client, the file manager on the client should automatically find the server.

Vsftpd

You can also auto-discover regular FTP servers, such as vsftpd. Install the vsftpd package and change the settings of vsftpd according to your own personal preferences (see this thread on ubuntuforums.org or vsftpd.conf(5)).

Create a .service file in /etc/avahi/services with the following contents:

/etc/avahi/services/ftp.service
<?xml version="1.0" standalone='no'?>
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service-group>
  <name>FTP file sharing</name>
  <service>
    <type>_ftp._tcp</type>
    <port>21</port>
  </service>
</service-group>

The FTP server should now be advertised by Avahi. You should now be able to find the FTP server from a file manager on another computer in your network. You might need to enable #Hostname resolution on the client.

AirPrint from Mobile Devices

Merge-arrows-2.pngThis article or section is a candidate for merging with AirPort#Printing .Merge-arrows-2.png

Notes: AirPrint is a feature provided by the Apple AirPort Express and by some printers. The manual configuration technique (using JetDirect) can also apply here and may be easier. (Discuss in Talk:Avahi#)

Avahi along with CUPS also provides the capability to print to just about any printer from airprint compatible mobile devices. In order to enable print capability from your device, simply create an Avahi service file for your printer in /etc/avahi/services/. An example of a generic services file for an HP-Laserjet printer would be similar to the following with the name, rp, ty, adminurl and note fields changed.

/etc/avahi/services/airprint.service
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service-group>
  <name>yourPrnterName</name>
  <service>
    <type>_ipp._tcp</type>
    <subtype>_universal._sub._ipp._tcp</subtype>
    <port>631</port>
    <txt-record>txtver=1</txt-record>
    <txt-record>qtotal=1</txt-record>
    <txt-record>rp=printers/yourPrnterName</txt-record>
    <txt-record>ty=yourPrnterName</txt-record>
    <txt-record>adminurl=http://198.168.7.15:631/printers/yourPrnterName</txt-record>
    <txt-record>note=Office Laserjet 4100n</txt-record>
    <txt-record>priority=0</txt-record>
    <txt-record>product=(GPL Ghostscript)</txt-record>
    <txt-record>printer-state=3</txt-record>
    <txt-record>printer-type=0x801046</txt-record>
    <txt-record>Transparent=T</txt-record>
    <txt-record>Binary=T</txt-record>
    <txt-record>Fax=F</txt-record>
    <txt-record>Color=T</txt-record>
    <txt-record>Duplex=T</txt-record>
    <txt-record>Staple=F</txt-record>
    <txt-record>Copies=T</txt-record>
    <txt-record>Collate=F</txt-record>
    <txt-record>Punch=F</txt-record>
    <txt-record>Bind=F</txt-record>
    <txt-record>Sort=F</txt-record>
    <txt-record>Scan=F</txt-record>
    <txt-record>pdl=application/octet-stream,application/pdf,application/postscript,image/jpeg,image/png,image/urf</txt-record>
    <txt-record>URF=W8,SRGB24,CP1,RS600</txt-record>
  </service>
</service-group>

Alternatively, https://raw.github.com/tjfontaine/airprint-generate/master/airprint-generate.py can be used to generate Avahi service files. It depends on python2 and python2-pycupsAUR. The script can be run using:

# python2 airprint-generate.py -d /etc/avahi/services
Note: If your printer under http://localhost:631/printers is "Not Shared", this python script won't output any file to /etc/avahi/services; in that case, you'll need to "Modify Printer" under one of the CUPS drop-down menus to turn sharing on. If that doesn't work, check out the ArchWiki on CUPS printer sharing.

Troubleshooting

Hostname changes with appending incrementing numbers

This is a known bug that is caused by a hostname race condition. One possible workaround is disabling IPv6 to attempt to prevent the race condition. If multiple interfaces are present use allow-interfaces to limit Avahi to a single interface. Another possible workaround is to disable the cache to prevent Avahi from checking for host name conflicts altogether, but this prevents Avahi from performing lookups.

See also