Multicast and Unicast DNS daemon



Runs on:

QNX Neutrino




The mdnsd daemon (also known as mDNSResponder on some systems) is a daemon invoked at boot time to implement Multicast DNS and DNS Service Discovery.

The mdnsd daemon listens on UDP port 5353 for Multicast DNS Query packets. When it receives a query for which it knows an answer, mdnsd issues the appropriate Multicast DNS Reply packet.

It also performs Unicast and Multicast DNS Queries on behalf of client processes, and maintains a cache of the replies.

The mdnsd daemon has no user-specifiable command-line arguments, and you shouldn't run it manually.


There are several methods that you can use to examine mdnsd's internal state for debugging and diagnostic purposes. The syslogd logging levels map as follows:

By default, only log level Error is logged.

A SIGUSR1 signal toggles additional logging, with Warning and Notice enabled by default:

kill -USR1 mdnsd

A SIGUSR2 signal toggles packet logging:

kill -USR2 mdnsd

A SIGINFO signal dumps a snapshot summary of the internal state to /var/log/system.log:

kill -INFO mdnsd

For more information on:

For the source code to mdnsd, see