# 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 the avahi package.

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

## 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 line:

    hosts: files dns myhostname

to:

    hosts: files mdns_minimal [NOTFOUND=return] dns myhostname

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 -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

### 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

### 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.

### Obtaining IPv4LL IP address

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

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`. 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 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 `man avahi.service`.

### 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).

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 `man vsftpd.conf`).

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

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-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.

## 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/lathiat/avahi/master/service-type-database/build-db.in
    wget https://raw.githubusercontent.com/lathiat/avahi/master/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-db.

    $./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

Hidden category:

- Pages or sections flagged with Template:Merge