Apple - DNS not resolving on Mac OS X

It turns out the solution was to bounce mDNSResponder:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

This was obtained by a different coworker from this Server Fault question.

OS X 10.10.0 – 10.10.3, Yosemite

Apparently, mDNSResponder doesn't exist in Yosemite (OS X 10.10). You can restart descoveryd instead to fix these issues.

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.discoveryd.plist

OS X 10.10.4+, Yosemite

In OSX 10.10.4 the mDNSResponder has been reintroduced. So use the first one will work again.

Actually, I think you might want to use

scutil --dns

scutil -r hostname

These commands use the dynamic store in configd, as opposed to the flatfiles in /etc, which often are only read in single user mode and for non networked systems.

man scutil   # or

scutil --help  

I've experienced the same problem… And while restarting mDNSResponder does seem to "work", restarting it a couple of times every hour sort of sucks.

So, for now, I've "solved" the problem by running dnsmasq locally. To do that:

• Build dnsmasq (download the tgz and make or brew install dnsmasq)

• Put this in a dnsmasq.conf file:

  resolv-file=resolv.conf
  user=nobody
  group=nobody
  interface=lo0
  cache-size=1024
  

• Put this in a resolv.conf file that is in the same directory as the dnsmasq.conf file (nb: not /etc/resolv.conf):

  nameserver 8.8.8.8
  nameserver 4.2.2.1
  nameserver 4.2.2.2
  

• Run dnsmasq with sudo dnsmasq --no-daemon --log-queries -C dnsmasq.conf. The output should look something like:

  ...
  dnsmasq: reading resolv.conf
  dnsmasq: using nameserver 4.2.2.1#53
  dnsmasq: using nameserver 4.2.2.2#53
  dnsmasq: using nameserver 8.8.8.8#53
  dnsmasq: read /etc/hosts - 6 addresses
  

• Open Network Preferences and make sure that 127.0.0.1 is the only DNS server (network preferences -> advanced -> DNS -> add 127.0.0.1)

Things should begin to work nicely again.

Once things are working, you can run dnsmasq without the --no-daemon and --log-queries options, so it will start in the background and you don't need to keep a Terminal window open.