.\" -*- tab-width: 4 -*-
.\" 
.\" Copyright (c) 2003-2012 Apple Inc. All Rights Reserved.
.\" 
.\" Licensed under the Apache License, Version 2.0 (the "License");
.\" you may not use this file except in compliance with the License.
.\" You may obtain a copy of the License at
.\" 
.\"     http://www.apache.org/licenses/LICENSE-2.0
.\" 
.\" Unless required by applicable law or agreed to in writing, software
.\" distributed under the License is distributed on an "AS IS" BASIS,
.\" WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
.\" See the License for the specific language governing permissions and
.\" limitations under the License.
.\"
.Dd Feb 25, 2018              \" 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
.Sh 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 SIGUSR1 signal will dump a snapshot summary of the internal state to 
.\" .Pa /var/log/system.log Ns :
.Xr syslog 8 .
.Pp
.Dl % sudo killall -INFO mDNSResponder
.Sh OPTIONAL ARGUMENTS
.Nm
accepts the following optional arguments:
.Bl -tag -width "AlwaysAppendSearchDomains"
.It Fl AlwaysAppendSearchDomains
Append search domains for multi-labeled Partially Qualified Domain Name as well as single-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.
.It Fl NoMulticastAdvertisements
Prevent the system from advertising Bonjour services via Multicast DNS.
.El
.Pp
To cause
.Nm
to run with these optional arguments when it launches on OS X 10.11 (El Capitan) and later, set the
.Sy AlwaysAppendSearchDomains
or
.Sy NoMulticastAdvertisements
boolean keys to true in /Library/Preferences/com.apple.mDNSResponder.plist and reboot.
.Pp
.Sh FILES
.Pa /usr/sbin/mDNSResponder
.Pa /Library/Preferences/com.apple.mDNSResponder.plist
.Pp
.Sh INFO
.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 Microsoft Windows,
Linux, FreeBSD, NetBSD, Solaris, and other POSIX systems.