What is mDNSResponder on a Mac, and how to flush the DNS cache
mDNSResponder handles every DNS lookup and Bonjour discovery. It was the second busiest network process on our Mac. How to flush DNS when sites will not load.
What is mDNSResponder?
Every time an app needs the address for a name, mDNSResponder looks it up and caches the answer. It also runs Bonjour, which finds printers, speakers, other Macs and shared drives on the local network. It lives at /usr/sbin/mDNSResponder and runs as _mdnsresponder.
| Reading on our Mac | Value |
|---|---|
| Received | 11.3 MB, second of all processes |
| Sent | 5.5 MB |
How do I flush the DNS cache on a Mac?
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponderIt clears cached lookups, so the next request asks fresh. Use it after changing DNS settings, when a site moved to a new server, or when one site fails while others work.
Why is mDNSResponder using network or CPU?
- Lots of lookups: a browser with many tabs, a crawler or a script.
- Bonjour on a busy network, with many devices announcing themselves.
- A VPN or filter changing DNS settings repeatedly.
See it live
Free Mac's System tab ranks every process by processor use and energy impact, once a second, and marks the ones macOS will not let you quit as protected. See also netbiosd and which app is using the internet.
Related: netbiosd and runningboardd.
Common questions
What is mDNSResponder on a Mac?
The macOS process for DNS lookups and Bonjour discovery of printers, speakers and other devices.
How do I flush DNS on a Mac?
Run sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder in Terminal.
Is mDNSResponder safe?
Yes. It is part of macOS and every network connection depends on it.