Flush DNS kills mDNSResponderHelper on macOS without a restart

[Stuart Anderson]

Enabling  "Flush DNS cache after connecting or disconnecting" under Tunnelblick 3.8.5a kills mDNSResponderHelper under Big Sur 11.3 after connecting or disconnecting, e.g., from /var/log/system.log,

May  1 13:01:11 Stuart-laptop com.apple.xpc.launchd[1] (com.apple.mDNSResponderHelper.reloaded[8442]): Service exited due to SIGHUP | sent by killall[9566]

However, this does not result in an automatic restart of mDNSResponderHelper and I have to manually pkill mDNSResponder to get the Helper started again. Hopefully there is a better way to flush the DNS cache.

[Tunnelblick developer]

That's peculiar – in all prior versions of macOS, mDNSResponderHelper restarts automatically after a killall -HUP.

[Stuart Anderson]

I can confirm that independent of Tunnelblick a manual sudo pkill mDNSResponderHelper does not result in an automatic restart on my Big Sur system. However, sudo pkill mDNSResponder does result in both processes restarting.

[Tunnelblick developer]

Tunnelblick does killall -HUP mDNSResponder followed by killall -HUP mDNSResponderHelper. It has done that for about three years.

Perhaps that needs to be done in the reverse order on Big Sur.

[Tunnelblick developer]

Stuart, are you running on X86 or M1?

[Stuart Anderson]

x86. It looks like a single call to killall with TERM instead of HUP does the trick on Big Sur,

Stuart-laptop:~> sudo killall -TERM mDNSResponder mDNSResponderHelper