I encountered a really strange issue with a Mac mini functioning as a small workgroup file server. The mini had dropped off the network and no-one could access it’s share points. I had the end user reboot it to see if that sorted it out and it didn’t so I went in and had a look at it in person.
When I got there, one of the first things I noticed is that there was no link light on the switch port that the mini was using. Strange… I tried different patch leads, both from the mini to the wall and from the patch panel to the switch. No go. I tried plugging the mini directly into the switch. Still no go. I looked in the Network prefpane, and sure enough, the mini was saying that there was no link for en0.
I tested the cables and switch port with my laptop and they all worked perfectly.
At this stage I was beginning to suspect a hardware issue. I can’t recall the last time I saw a failed Ethernet port on a mini, but anything is possible. I checked Time Machine to make sure there was a recent backup before attempting anything else and there were some errors in Time Machine as well.
I reset the Time Machine backups and Time Machine kept coming up with an error, every time I tried to tell it to back up to the external hard drive — Time Machine could not be configured. The built-in network interface could not be found.
Yes, I know that the network interface can’t be found, that’s why I want to back up! I deleted the Ethernet interface and tried again – same error message. I re-added it to the system preferences and still the same error message. I thought that it was strange that you couldn’t run a Time Machine backup if your machine wasn’t connected to a network, so it was time for some googling.
Apple have a knowledge base article Time Machine: Troubleshooting backup issues that was exactly what I was looking for.
Red “i” message: “Time Machine could not be configured. The built-in network interface could not be found”
From the Finder’s Go menu go to this location:
- Copy the file “NetworkInterfaces.plist” to the desktop (to make a precautionary backup).
- Delete the file “NetworkInterfaces.plist”. Enter administrator name and password if prompted.
Restart your Mac.
- Once restarted, reconfigure your the Network and Time Machine preference panes in System Preferences.
- If the issue persists, contact an Apple Authorized Service Provider to have your Mac’s network ports checked.
Sure enough, deleting /Library/Preferences/SystemConfiguration/NetworkInterfaces.plist, rebooting and then setting the preferences in System Preferences fixed everything as good as new.