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Comment by germanier | Hacker News Reader

Could someone add some context please? I see that apparently the method to flush the DNS cache changes between versions. Is there a deeper reason why this is necessary?

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Basically:

* Snow Leopard and earlier use lookupd for DNS resolving (`dscacheutil -flushcache`)

* Since Lion, they switched from lookupd to mDNSResponder, presumably for Bonjour protocol support (`killall -HUP mDNSResponder`)

* Yosemite switched to discoveryd that basically is a rewrite of mDNSResponder (`discoveryutil mdnsflushcache`)

* Due to a lot of problems with discoveryd, they switched from discoveryd back to mDNSResponder since v10.10.4 (so we're back to `killall HUP mDNSResponder`)

https://support.apple.com/en-us/HT202516

I'm not sure. The `dscacheutil -flushcache` command he lists for Snow Leopard still works for me (OS X Yosemite here).

And it still works for me on macOS 10.12.

So I see absolutely no point here.

The command doesn't fail but does it actually flush the DNS cache, or does it flush the Directory Cache which isn't used for DNS anymore (or possibly at all, on my El Cap machine flushing succeeds but any query of the cache content or its statistics replies "Unable to get details from the cache node")

The command did flush the Directory Service cache, but DNS is no longer part of it. You can still use its query command though.

    dscacheutil -q host -a name www.example.com

On the topic, easiest way to see if dscacheutil -flushcache work or not is to probably do something like:

    dscacheutil -q host -a name www.example.com
    # Make sure it's in the cache prior to running.
    
    sudo dscacheutil -flushcache
    dscacheutil -q host -a name www.example.com
    # Notice if there's a slight delay for the lookup.
    
    sudo killall -HUP mDNSResponder
    dscacheutil -q host -a name www.example.com
    # Notice if there's a slight delay for the lookup.

"macOS" has a tendency to cache stale DNS. But over the years they have changed the commands to flush the cache, so you end up googling how to clear the cache, checking your version of osx, and pray to the DNS gods that it will work this time.

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