---
name: "mDNSResponder"
section: "8"
platform: "macos"
package: "mDNSResponder"
version: "2881.120.11"
release: "macOS 26.5"
platforms: ["macos"]
url: "https://new.carta.tech/mDNSResponder"
---

# mDNSResponder(8)

Multicast and Unicast DNS daemon

## 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)](/syslog/1.md) 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)](/syslog/1.md) 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 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.

- **-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, **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 platforms, including Microsoft Windows, Linux, FreeBSD, NetBSD, Solaris, and other POSIX systems.