Avahi - ArchWiki

# Avahi

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 avahi from the official repositories.

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

### Enable IPv6

For some reason, Avahi comes with IPv6 disabled by default. To enable it, set `use-ipv6` to `yes` in `/etc/avahi/avahi-daemon.conf`.

## Using Avahi

### Obtaining IPv4LL IP address

This article or section is a candidate for merging with dhcpcd.

Notes: should be merged into the main page (Discuss)

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

### Hostname resolution

Avahi also allows you to access computers using their hostnames. This is how to enable it.

Note: Using Avahi for IPv6 hostname resolution is severly limited and not really usable.[1] (summary: you cannot do something trivial as `ping6 archy.local`)

Install the nss-mdns package and start `avahi-daemon.service` using systemd.

Suppose you have machines with names maple, fig and oak, all running Avahi. Avahi can be set up so that you do not have to manage a `/etc/hosts` file for each computer. Instead you can simply use `maple.local` to access whatever services maple has.

However by default, `.local` querying is disabled in Arch Linux. To enable support for .local, edit the file `/etc/nsswitch.conf` and change the line:

    hosts: files dns myhostname

to:

    hosts: files mdns_minimal [NOTFOUND=return] dns myhostname

#### Additional info about mdns

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 have configured Avahi to use a different TLD, you should replace `mdns_minimal [NOTFOUND=return]` with the full `mdns` module. There also are IPv4-only and IPv6-only modules `mdns[46](_minimal)`.

#### Tools

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

    avahi-browse -alr

to discover services in your network.

The Avahi Zeroconf Browser (`avahi-discover` – note that it needs avahi's optional dependencies pygtk and python2-dbus) shows the various services on your network. You can also browse SSH and VNC Servers using `bssh` and `bvnc` respectively.

There's a good list of software with Avahi support at their website: http://avahi.org/wiki/Avah4users

### 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 OS X). 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 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 a script is available. This was based upon this post.

#### Samba

Should work out-of-the-box.

#### GShare

You can grab 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

Sourced from 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

    <?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>

When you are done, restart the `avahi-daemon.service` and `vsftpd.service` services.

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 this section).

#### 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 giver.

Note that this depends on gnome-sharp, which has heavy GNOME dependencies.

### 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 for a list of clients supporting the bonjour protocol.

### 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 /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:

    <?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 pycups. 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.

### Firewall

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 `*.service` files are found in `/etc/avahi/services`. 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 RFC865 on TCP port 17 which you are running on your machine

The first thing to do is to determine the `<type>`. `man avahi.service` 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 RFC865) is 17.

Our `qotd.service` file is thus:

    <?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>

      <servi
        <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 `man avahi.service`.

#### Modifying the service-types database

As noted above, avahi comes with tools to browse advertised services. Both `avahi-browse` and `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 `avahi-browse -a` would show the following ugly entry

    + wlp2s0 IPv4 MyServer                                        _qotd._tcp local

##### Getting the Sources

First, download the files `build-db.in` and `service-types` files from the `service-type-database` subdirectory in the 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 `service-types` file. This file has one entry per line, with the entries in the format `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 `build-db` python script (be sure to use python2 not python3). This will build the `service-types.db` file. Check to make sure it's been built and use `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 `avahi-browse` database dump command to make sure avahi sees the new entry:

    $cp /usr/lib/avahi/service-types.db /backup-directory
    $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 `avahi-browse` should now be:

    + wlp2s0 IPv4 MyServer                                        Quote of the Day (QOTD) Server local

## See also

- Avahi - Official project website
- Wikipedia entry
- Bonjour for Windows - Enable Zeroconf on Windows
- http://www.zeroconf.org/

Category:

- Networking