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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 Mul-ticast Multicast
     ticast DNS and DNS Service Discovery. On Mac OS X 10.6 (Snow Leopard), mDNSResponder is also the sys-tem-wide system-wide
     tem-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 main-tains maintains
     tains a cache of the replies.

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

     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 /var/log/system.log:

           % 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 Discovery 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 officially supported by Apple) are
     mDNSResponder daemons for other platforms, including Mac OS 9, Microsoft Windows, Linux, FreeBSD,
     NetBSD, Solaris, and other POSIX systems.

Darwin                         October 11, 2013                         Darwin

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