mDNSResponder fan loud 100% CPU

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Level 1

45 points

mDNSResponder fan loud 100% CPU

For the last year it seems that at least once a week or more I am having to kill the mDNSResponder process by CLI sudo "killall -HUP mDNSResponder" after the fan begins to sing when it becomes CPU hunger. Lately, like last night when using my MacBook Pro for the day and closed down for the night around 6pm. Sometime after 8pm I noticed my CPU fan loud trying to cool the CPU. This morning I get on and its still running hard. I tried to stop the process inside Active Monitor with normal and force but does noting. I always have to use the CLI to kill the process.

What is the purpose of mDNSResponder and can I turn it off. My MBP connected to my cell phone for calls and text, besides that nothing else. I get really annoying that it picks up at night and runs when its closed down.

MacBook Pro (2020 and later)

Posted on Dec 7, 2021 6:11 AM

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Answer 1

John Galt

Level 10

158,156 points

Dec 9, 2021 12:51 AM in response to MauWoW

It is an overly broad description, but that process is used for Macs to discover and connect to other devices. It sounds as though you already knew that, and the fact it shouldn't be running amok. Using "killall -HUP mDNSResponder" clearly isn't a practicable solution either.

The reason it's running away is anyone's guess. Try using EtreCheck: Using EtreCheck - Apple Community. Post its report in a reply to this Discussion.

Needless to say, if you are using, or have used at any time in the past, any non-Apple "anti-virus", "cleaning", or "Internet security" products including "banking security", anything at all in that broad category of utterly useless garbage, don't. A lot of things won't work if you do.

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Answer 2

MauWoW Author

Level 1

45 points

Dec 10, 2021 5:37 AM in response to John Galt

Yeah kind of broad but I don't understand why it is doing it. It happened again this morning where the keys are hot and the finger print reader could burn my finger. This weekend I think I am going to buy a keyboard and mouse since it takes a few hours to cool so my hands are not sweating all over everything.

I don't run anything to crazy. No Antivirus software. The machine is used for work and I have VMs for questionable things as a sandbox. I had this same issue with my last MBP which is why I purchased this one last January. But it started a week after purchase and the OS updates, I feel had no effect on it. Just figured this was a common problem with something that needed disabled I was not finding in my searches.

I added the Etrecheck. When I ran the check I watched mDNSResponder lose its 100% process hold. Fan has slowed down a bit but still working harder than normal usage.

EtherCheck

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Answer 3

John Galt

Level 10

158,156 points

Dec 11, 2021 7:01 AM in response to MauWoW

System modifications - There are a large number of system modifications running in the background.

In situations such as this a process of elimination is required. Anything that modifies a stock Mac becomes a culprit, and it's nearly certain one or more of those background tasks is conflicting with mDNSResponder.

First please determine if you observe the same problem while running your Mac in "Safe Mode": How to use safe mode on your Mac. It is nearly certain the problem will not manifest while in that mode. Please confirm, and then restart your Mac normally (not "Safe Mode"). Then, observe again. It is nearly certain to reappear.

Confirm both those assumptions before proceeding with a process of elimination. Begin with the Cisco AnyConnect software. Uninstall it according to its instructions, then restart your Mac. Run EtreCheck again to confirm it has been completely removed. Observe and test. Justification for suspecting the Cisco product is that it's a networking app; of course lots of things are, but you have to start somewhere and that one is obviously running all the time.

Microsoft OneDrive, "Teams" and all its associated processes might also be contributing factors.

After uninstalling those things, you can always reinstall them again if they don't turn out to be a cause.

If you don't resolve the problem please write back for more suggestions.

Back up your Mac as a matter of course. To learn how to use Time Machine please read Back up your files with Time Machine on Mac.

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mDNSResponder fan loud 100% CPU

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