FromWikipedia:Avahi (software):

Avahi is a freeZero-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 theavahi package andenable theavahi-daemon.service or usesocket activation.

Using Avahi

Hostname resolution

Avahi provides local hostname resolution using a "hostname.local" naming scheme. To enable it, install thenss-mdns package andstart/enableavahi-daemon.service.

Then, edit the file/etc/nsswitch.conf and change thehosts line to includemdns_minimal [NOTFOUND=return] beforeresolve anddns:

hosts: mymachinesmdns_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] files myhostname dns

Configuring mDNS for custom TLD

Themdns_minimal module handles queries for the.local TLD only. Note the[NOTFOUND=return], which specifies that ifmdns_minimal cannot find*.local, it will not continue to search for it indns,myhostname, etc.

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

• replacemdns_minimal [NOTFOUND=return] with the fullmdns module. There also are IPv4-only and IPv6-only modulesmdns[46](_minimal)
• customize/etc/avahi/avahi-daemon.conf with thedomain-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 this to discover services in your network:

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

If this command yields nothing, it is likely due to afirewall blocking mDNS traffic.

If you just want to do an mDNS query to resolve a .local hostname to an IP address (similar todig ornslookup), use:

$ avahi-resolve-host-namesome-host-name.local

Note that thegetent hosts command can do both DNS and mDNS lookups.

The Avahi Zeroconf Browseravahi-discover shows the various services on your network. Note that it needs Avahi's optional dependenciesgtk3,python-dbus andpython-gobject. You can also browse SSH and VNC Servers usingbssh andbvnc respectively.

Firewall

Be sure to open UDP port5353 if you are using afirewall.

Link-Local (Bonjour/Zeroconf) chat

Avahi can be used for Bonjour protocol support under Linux. CheckWikipedia:Comparison of instant messaging clients orList of applications/Internet#Instant messaging clients for a list of clients supporting the Bonjour protocol.

Obtaining IPv4LL IP address

Thedhcpcd client 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, runavahi-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 theavahi 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 us say you wanted to advertise a quote of the day (QOTD) service operating perRFC:865 on TCP port17 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 theDNS-SD register was merged into the IANA register in 2010, we look for the service name on theIANA register or in/etc/services file. The service name shown there isqotd. Since we are running QOTD on tcp, we now know the service is_qotd._tcp and the port (per IANA and RFC 865) is17.

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, consultavahi.service(5).

Keep in mind that Avahi does not support arbitrary strings in the <type> field, you can only set values known inservice database of Avahi. If you want to register something custom you will likely have to edit the database definition, build an updated version and distribute it to your hosts.

SSH

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

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

File sharing

NFS

If you have anNFS 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 asGNOME/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 haveinsecure as an option in your/etc/exports; otherwise, it needs to be changed (note thatinsecure 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, howevera script is available. This was based uponthis 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 asvsftpd. Install thevsftpd package and change the settings of vsftpd according to your own personal preferences (seethis thread on ubuntuforums.org orvsftpd.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.

Troubleshooting

Hostname changes with appending incrementing numbers

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

systemd-resolved prevents nss-mdns from working

nss-mdns only works if the DNS server listed in/etc/resolv.conf returnsNXDOMAIN to SOA queries for the "local" domain.[1]

Check if your configured DNS server answers the SOA query for the "local" domain withNXDOMAIN first. For example:

$ host -t SOA local

If the DNS server responds withNXDOMAIN, you do not need to follow the steps below.Avahi should be able to find resources in the network normally, even if usingsystemd-resolved.

In older versions ofsystemd-resolved the global setting forMulticastDNS=no inresolved.conf(5) lead to Avahi-incompatible response codes for the "local" domain. This resulted in Avahi not finding resources (printers) correctly. Seesystemd issue 21659 for reference.

However, if the DNS query above fails to returnNXDOMAIN for the "local" domain, you can use the fullmdns NSS module instead ofmdns_minimal and create/etc/mdns.allow to allow only the "local" domain. For example:

/etc/nsswitch.conf

hosts: mymachinesmdns [NOTFOUND=return] resolve [!UNAVAIL=return] files myhostname dns

/etc/mdns.allow

.local..local

ECONNREFUSED (Connection refused) on avahi socket

If your Avahi instance starts and operates correctly, but nss does not seem to forward requests to mdns, this may be caused by stuck socket/run/avahi-daemon/socket. This can be verified e.g. with strace. In this case you may have torestart bothavahi-daemon.service andavahi-daemon.socket to make it work correctly.

KDE Connect's built in mDNS conflicts

If you usekdeconnect, there are mDNS conflicts with avahi as kdeconnect also runs its mdns server. This can cause hostname conflicts, like renaming your host tomyhostname-2 after network restarts.

To correct this, either removekdeconnect, or build a version without mDNS support, like inkdeconnect-no-mdns^AUR.

Seekde bug 487719.

See also

• Avahi - Official project website
• Wikipedia:Avahi (software)
• iTunes (includes Bonjour) - Enable Zeroconf on Windows
• http://www.zeroconf.org/

• Multicast DNS

• Pages or sections flagged with Template:Merge