AlwaysAppendSearchDomains

2017-08-08 With thanks to Randy Fay. Sierra and above complains when you try to unload the mDNSResponder because of System Integrity Protection (SIP):

/System/Library/LaunchDaemons/com.apple.mDNSResponder.plist: Operation not permitted while System Integrity Protection is engaged

If you choose to disable SIP to complete the steps in Pieter's updated fix, you need to follow Apple's instructions (from https://developer.apple.com/library/content/documentation/Security/Conceptual/System_Integrity_Protection_Guide/ConfiguringSystemIntegrityProtection/ConfiguringSystemIntegrityProtection.html):

1. Shut down fully
2. Start up while holding down Command-R
3. Choose Utilities > Terminal from the menu bar
4. Type the commands:
   • csrutil disable
   • reboot

Then follow Pieter's steps below, and then re-enable SIP afterwards by repeating the above using "csrutil enable" instead.

2016-10-18 With thanks to Pieter Lange, there's a new and better way to do this, please ignore the scripts if you're on a modern version of MacOS.

The intention is to fix a behaviour in MacOSX when accessing resources (web sites, servers) with a name of the form aaa.bbb where the true hostname is in fact aaa.bbb.search.domain.

This bug means for example you can use nslookup to resolve a hostname but when you try to ping the same hostname the Mac complains it can't resolve the addres. Very peculiar.

For details please see:

• http://apple.stackexchange.com/questions/50457/nslookup-works-ping-and-ssh-dont-os-x-lion-10-7-3
• http://www.eigenspace.org/2011/07/fixing-osx-lion-dns-search-domains/
• http://www.makingitscale.com/2011/broken-search-domain-resolution-in-osx-lion.html

The 'new way' in macOS Sierra (and tested also in El Capitan) to do this is to run (in Terminal):

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo defaults write /Library/Preferences/com.apple.mDNSResponder.plist AlwaysAppendSearchDomains -bool YES
sudo launchctl load /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

And to revert to the default behaviour:

sudo launchctl unload /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo defaults write /Library/Preferences/com.apple.mDNSResponder.plist AlwaysAppendSearchDomains -bool NO
sudo launchctl load /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

For anyone remaining on an older version of MacOS X, the scripts described below have been moved to the "older" folder.

To apply the changes:

1. Open Terminal.app
2. cd <directory holding the scripts>
3. ./AlwaysAppendSearchDomains.sh

To remove the changes and restore the default configuration:

1. Open Terminal.app
2. cd <directory holding the scripts>
3. ./uninstall.sh

This script may ask for your administrator password (if you have not recently authenticated), and will update a single file (/System/Library/LaunchDaemons/com.apple.mDNSResponder.plist) before restarting the name resolution system on your machine.

Originally written by Mike Thomson (mike@m-thomson.net)