Avahi — Zero-Config mDNS/DNS-SD (Bonjour)

Avahi is active by default — your machine is immediately reachable as hostname.local on the LAN. It is used by CUPS (printers), KDE Connect, DLNA media servers, and SSH discovery tools.

Discovering Services

# Discover all services on the network (live view, Ctrl-C to stop)
avahi-browse -a

# One-shot (exit after listing all found services)
avahi-browse -at

# Filter by service type
avahi-browse _http._tcp    # HTTP services
avahi-browse _ssh._tcp     # SSH servers
avahi-browse _smb._tcp     # Samba shares
avahi-browse _ipp._tcp     # Printers

# Resolve hostnames alongside service discovery
avahi-browse -at -r

Name Resolution

# Resolve a .local hostname to IP
avahi-resolve --name myhostname.local

# Reverse lookup (IP → hostname)
avahi-resolve --address 192.168.1.50

# Check daemon status
sudo systemctl status avahi-daemon

# Restart after config changes
sudo systemctl restart avahi-daemon

Publishing a Custom Service

Create /etc/avahi/services/myservice.service:

<?xml version="1.0" standalone='no'?>
<service-group>
  <name>My Web Server</name>
  <service>
    <type>_http._tcp</type>
    <port>8080</port>
  </service>
</service-group>

Avahi auto-reloads service files from /etc/avahi/services/ — no daemon restart is needed after adding or editing a file.

Disabling Avahi (Reduce Attack Surface)

If you do not need .local discovery on a given machine:

sudo systemctl disable --now avahi-daemon

Note: Disabling Avahi will prevent CUPS printer auto-discovery and KDE Connect device detection on the LAN.

Troubleshooting

| Issue | Solution | |-------|----------| | hostname.local not resolving from another machine | Ensure avahi-daemon is running; check that your firewall allows UDP 5353 (mDNS) — the mdns firewalld service covers this | | Services not appearing in avahi-browse -a | Confirm the remote service publishes via mDNS; some services require explicit Avahi service files | | Name collision (hostname-2.local) | Two devices share the same hostname — rename one via hostnamectl set-hostname newname | | Avahi flooding logs with errors | Check /etc/nsswitch.conf — mdns4_minimal should appear before dns in the hosts: line |