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).
Contents
Installation
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
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 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
$ 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
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
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/