This totally rocks, as instead of having a number of bookmarks for various administration pages on my machines, the machines can export them over Zeroconf and when I am at home and those machines are on, they'll appear magically.

The first step to having Zeroconf enlightenment is to ensure avahi-daemon is installed on all machines. It doesn't matter if there are some machines that it cannot be installed on (i.e. router running embedded software), as other machines can publish their name and services on their behalf.

The first service I published is the web-based admin pages for my printer. The printer is connected to a small server called Melchett (a Buffalo LinkStation) which is running CUPS. By creating /etc/avahi/services/cups.service on Melchett with the following contents, the web site is published:

<?xml version="1.0" standalone='no'?>
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
<service-group>
  <name>Epson Stylus Photo R220 Admin</name>
  <service>
    <type>_http._tcp</type>
    <port>631</port>
    <txt-record>path=/printers/epson-stylus-photo-r220</txt-record>
  </service>
</service-group>

Each .service file in /etc/avahi/services defines a group of services. A group has a name, and a set of services. Each service has a number of properties:

Type

Specifies what the type of the service is (_http._tcp is HTTP over TCP). There is a canonical list of types available. This is a required element.

Port

What port the service is listening on. This is a required element, there is no default port 80 for _http._tcp services.

Text Record

This sets arbitary key-value pairs, which are interpreted on a per-service manner. For _http._tcp services the valid keys are u (username), p (password) and path.

There are also domain-name and host-name properties, but these are not used in this service description as the service is on the local machine.

In summary, you can see that I have specified that there is a web page accessible via HTTP on this machine, available on port 631 at the path /printers/epson-stylus-photo-r220. When other machines search the network for web pages they'll find this service entry (with the hostname properties filled in by Avahi), and generate the URL http://melchett.local:631/printers/epson-stylus-photo-r220 A quick pop into Epiphany shows that this is indeed the case, there is now a Local Sites category in the bookmarks containing Epson Stylus Photo R220 Admin.

There is one other thing I need to explain: how to publish services on behalf of other machines. Until this afternoon this required something to run avahi-publish-address to give the machine a Zeroconf name, but this afternnon Trent committed static name mapping to Avahi. When this is in a released version, I'll continue this article.