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.\" Copyright (c) 2003-2004 Apple Computer, Inc. All Rights Reserved.
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.\" $Log: mDNSResponder.8,v $
.\" Revision 1.10  2009/04/20 16:12:13  mcguire
.\" <rdar://problem/6807798> manpage: roff errors
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.\" Revision 1.9  2009/04/11 00:20:27  jessic2
.\" <rdar://problem/4426780> Daemon: Should be able to turn on LogOperation dynamically
.\"
.\" Revision 1.8  2006/10/06 17:31:33  mkrochma
.\" <rdar://problem/4769407> Typo in man page for mDNSResponder(8)
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.\" Revision 1.7  2006/08/14 23:24:56  cheshire
.\" Re-licensed mDNSResponder daemon source code under Apache License, Version 2.0
.\"
.\" Revision 1.6  2005/02/10 22:35:28  cheshire
.\" <rdar://problem/3727944> Update name
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.\" Revision 1.5  2004/06/29 02:41:38  cheshire
.\" Add note that mDNSResponder is called mdnsd on some systems
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.\" Revision 1.4  2004/05/18 18:14:36  cheshire
.\" Minor wording update
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.\" Revision 1.3  2004/04/22 02:56:08  cheshire
.\" <rdar://problem/3619494>: mDNSResponder man page format error
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.\" Revision 1.2  2004/04/12 18:03:24  ksekar
.\" <rdar://problem/3619494>: mDNSResponder man page format error
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.\" Revision 1.1  2003/11/13 03:21:38  cheshire
.\" <rdar://problem/3086886>: No man page for mDNSResponder
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.\"
.\"
.Dd April 2004              \" Date
.Dt mDNSResponder 8         \" Document Title
.Os Darwin                  \" Operating System
.\"
.Sh NAME
.Nm mDNSResponder
.Nd Multicast and Unicast DNS daemon    \" Name Description for whatis database
.\" 
.Sh SYNOPSIS
.Nm
.\"
.Sh DESCRIPTION
.Nm
(also known as
.Nm 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), 
.Nm 
is also the system-wide Unicast DNS Resolver.
.Pp
.Nm
listens on UDP port 5353 for Multicast DNS Query packets.
When it receives a query for which it knows an answer,
.Nm
issues the appropriate Multicast DNS Reply packet.
.Pp
.Nm
also performs Unicast and Multicast DNS Queries on behalf of client processes, and 
maintains a cache of the replies.
.Pp
.Nm
has no user-specifiable command-line argument, and users should not run
.Nm
manually.
.Pp
.Ss LOGGING
There are several methods with which to examine 
.Nm Ns 's internal state for debugging and diagnostic purposes. The syslog(1)
logging levels map as follows:
.Pp
.Dl Error - Error messages
.Dl Warning - Client-initiated operations
.Dl Notice - Sleep proxy operations
.Dl Info - Informational messages
.Pp
By default, only log level Error is logged.
.Pp
A SIGUSR1 signal toggles additional logging, with Warning and Notice
enabled by default:
.Pp
.Dl % sudo killall -USR1 mDNSResponder
.Pp
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:
.Pp
.Dl % sudo syslog -c mDNSResponder -d
.Pp
A SIGUSR2 signal toggles packet logging:
.Pp
.Dl % sudo killall -USR2 mDNSResponder
.Pp
A SIGINFO signal will dump a snapshot summary of the internal state to 
.Pa /var/log/system.log Ns :
.Pp
.Dl % sudo killall -INFO mDNSResponder
.Sh FILES
.Pa /usr/sbin/mDNSResponder \" Pathname
.\"
.Sh SEE ALSO
.Xr mDNS 1
.Pp
For information on Multicast DNS, see
.Pa http://www.multicastdns.org/
.Pp
For information on DNS Service Discovery, see
.Pa http://www.dns-sd.org/
.Pp
For information on how to use the Multicast DNS and the
DNS Service Discovery APIs on Mac OS X and other platforms, see
.Pa http://developer.apple.com/bonjour/
.Pp
For the source code to
.Nm , see
.Pa http://developer.apple.com/darwin/projects/bonjour/
.\"
.Sh BUGS
.Nm
bugs are tracked in Apple Radar component "mDNSResponder".
.\"
.Sh HISTORY
The
.Nm
daemon first appeared in Mac OS X 10.2 (Jaguar).
.Pp
Also available from the Darwin open source repository
(though not officially supported by Apple) are 
.Nm
daemons for other platforms, including Mac OS 9, Microsoft Windows,
Linux, FreeBSD, NetBSD, Solaris, and other POSIX systems.