manpagez: man pages & more
man mDNSResponder(8)
Home | html | info | man
mDNSResponder(8)          BSD System Manager's Manual         mDNSResponder(8)


     mDNSResponder -- Multicast and Unicast DNS daemon




     mDNSResponder (also known as mdnsd on some systems) is a daemon invoked
     at boot time to implement Multicast DNS and DNS Service Discovery. On Mac
     OS X 10.6 (Snow Leopard), mDNSResponder is also the system-wide Unicast
     DNS Resolver.

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

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

     mDNSResponder has no user-specifiable command-line argument, and users
     should not run mDNSResponder manually.


     There are several methods with which to examine mDNSResponder's internal
     state for debugging and diagnostic purposes. The syslog(1) logging levels
     map as follows:

           Error - Error messages
           Warning - Client-initiated operations
           Notice - Sleep proxy operations
           Info - Informational messages

     By default, only log level Error is logged.

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

           % sudo killall -USR1 mDNSResponder

     Once this logging is enabled, users can additionally use syslog(1) to
     change the log filter for the process. For example, to enable log levels
     Emergency - Debug:

           % sudo syslog -c mDNSResponder -d

     A SIGUSR2 signal toggles packet logging:

           % sudo killall -USR2 mDNSResponder

     A SIGINFO signal will dump a snapshot summary of the internal state to

           % sudo killall -INFO mDNSResponder




     For information on Multicast DNS, see

     For information on DNS Service Discovery, see

     For information on how to use the Multicast DNS and the DNS Service Dis-
     covery APIs on Mac OS X and other platforms, see

     For the source code to mDNSResponder, see


     mDNSResponder bugs are tracked in Apple Radar component "mDNSResponder".


     The mDNSResponder daemon first appeared in Mac OS X 10.2 (Jaguar).

     Also available from the Darwin open source repository (though not offi-
     cially supported by Apple) are mDNSResponder daemons for other platforms,
     including Mac OS 9, Microsoft Windows, Linux, FreeBSD, NetBSD, Solaris,
     and other POSIX systems.

Darwin                         September 3, 2012                        Darwin

Mac OS X 10.8 - Generated Mon Sep 3 14:54:31 CDT 2012
© 2000-2024
Individual documents may contain additional copyright information.