mDNSResponder(8)          BSD System Manager's Manual         mDNSResponder(8)

NAME
     mDNSResponder -- Multicast and Unicast DNS daemon

SYNOPSIS
     mDNSResponder

DESCRIPTION
     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.

LOGGING
     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

OPTIONAL ARGUMENTS
     mDNSResponder accepts the following optional arguments:

     -AlwaysAppendSearchDomains
                                Append search domains for multi-labeled Par-
                                tially Qualified Domain Name as well as sin-
                                gle-labeled Partially Qualified Domain Name.
                                This argument is not recommended because of
                                the extra DNS traffic it generates and its
                                adverse effect on battery life.

     -NoMulticastAdvertisements
                                Prevent the system from advertising Bonjour
                                services via Multicast DNS.

     To cause mDNSResponder to run with these optional arguments when it
     launches on OS X 10.11 (El Capitan) and later, set the
     AlwaysAppendSearchDomains or NoMulticastAdvertisements boolean keys to
     true in /Library/Preferences/com.apple.mDNSResponder.plist and reboot.

FILES
     /usr/sbin/mDNSResponder
     /Library/Preferences/com.apple.mDNSResponder.plist

INFO
     For information on Multicast DNS, see http://www.multicastdns.org/

     For information on DNS Service Discovery, see http://www.dns-sd.org/

     For information on how to use the Multicast DNS and the DNS Service Dis-
     covery APIs on Mac OS X and other platforms, see
     http://developer.apple.com/bonjour/

     For the source code to mDNSResponder, see
     http://developer.apple.com/darwin/projects/bonjour/

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

HISTORY
     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 Microsoft Windows, Linux, FreeBSD, NetBSD, Solaris, and other
     POSIX systems.

Darwin                         November 14, 2024                        Darwin