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 lev-
     els 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 Partially Qualified Domain Name as well as single-labeled Partially Quali-
				fied 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 Discovery 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 officially supported by Apple) are mDNSResponder daemons for other plat-
     forms, including Microsoft Windows, Linux, FreeBSD, NetBSD, Solaris, and other POSIX systems.

Darwin								   June 1, 2019 							    Darwin