My Mac mini's computer name keeps changing when it resumes from sleep When I wake my Mac mini from sleep, it occasionally comes up with a dialog saying "The name of your computer "whatever" is already in use on this network. The name has been changed to "whatever (1)"" (or (2), I'm up to (4) at the moment).

The Mac is plugged in to the network via an ethernet cable and gets a DHCP assigned IP address from my router which runs pfSense. I have DHCP set to give the same IP address to the Mac's Mac.

Why does this happen, and more usefully, how can I make the machine stop renaming itself?

In System Preferences - Sharing I have 'File sharing' and 'Remote Login' enabled.
I've seen this happen when the local DNS server has DNS caching enabled, but doesn't flush the cache often enough (or at all).

You can set your Host Name/Computer Name to a static value using scutil in Terminal. This means that your Mac will no longer change it's name automatically, so it's important that there are no other machines on your network that actually have that hostname. When you run this, replace "new_hostname" with your desired hostname:

sudo scutil --set HostName new_hostname

sudo scutil --set LocalHostName new_hostname

sudo scutil --set ComputerName new_hostname


You can check to make sure the values are set by running:

scutil --get HostName 

scutil --get LocalHostName 

scutil --get ComputerName 


Sources: man scutil

https://developer.apple.com/library/mac/documentation/Darwin/Reference/Manpages/man8/scutil.8.html

http://osxdaily.com/2010/09/06/change-your-mac-hostname-via-terminal/