The Mac OS X v10.6.7 Update is recommended for all users running Mac OS X Snow Leopard and includes general operating system fixes that enhance the stability, compatibility, and security of your Mac.
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
FILES
/usr/sbin/mDNSResponder
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 Mac OS 9, Microsoft Windows, Linux, FreeBSD, NetBSD, Solaris, and other POSIX systems.
Darwin June 1, 2019 Darwin
