The problem involved Time Machine. The Mac was a brand-new MacBook Pro Retina and the Time Machine backup was set to use a Time Capsule for storage. The initial backup progressed a tiny bit (500 MB) but wouldn’t go further. By the time I got there to trouble-shoot the estimated time for the initial backup was reported as 122 days.
Funny thing was, everything looked right. The Time Capsule disk was chosen in the Time Machine Preference Pane, there was plenty of room on the Time Capsule, and the connection to the Time Capsule, while wireless, was very strong. Restarting the Mac did not help and neither did restarting the Time Capsule. It was a real head-scratcher.
Out of the blue I had the idea of checking the contents of the Time Capsule. In the Backups.backupdb folder I found backups representing other Macs, but none representing the new Mac. That seemed odd: every backed-up machine should have a folder on the backup drive with its name on it, as shown below (for my Mac’s backup).
And where does Time Machine get the name of the machine? From the Sharing Preference Pane, that’s where. Here’s what MY Mac’s Sharing Preference Pane shows. You’ll note that my Mac’s backup folder has EXACTLY the same name as shown in the “Computer Name” section below (because Time Machine just reads the Computer Name and creates the backup folder to match).
When I looked at the Sharing Preference Pane on the MacBook Pro that wouldn’t back up the Computer Name was completely blank. Completely! No one knew why it was blank, but blank it was. And as soon as I entered a Computer Name for the MacBook Pro the Time Machine backup got back to work. The time remaining went from 122 days to 8 hours to 7 hours to 6 hours in the space of twenty minutes. The owner reported a completed backup the next day and it’s been backing up fine ever since.
The moral of the story is you have to have a Computer Name, in the Sharing Preference Pane, if you want Time Machine to work.