Yosemite upgrade fails at late stage, unable to get out of re-try loop I was running Mavericks on MacBook Pro (mid 2012 model). I started upgrade to Yosemite. All seemed well on download, and the laptop re-booted to complete the install. The installation screen with OSX logo appears, and progress got to over 90% complete, with "2 minutes remaining" displayed. It remained like that for around 2 hours, before I decided something was likely wrong.

I have started the machine a few times, and by default it boots back to try the install again, and stops in the exact same place.

I have also started the recovery disk ( cmd-R ), checked for and repaired some permissions errors (that looked unrelated), and have also run a full install of Yosemite from the menu, which apparently succeeded. However, the machine still boots to same attempt to complete the install - I'm assuming this is the original upgrade that still expects to be completed.

I have not been in this position with a Mac before, and am not sure what my next steps are:

1) Is there any safe way out of the installation loop?

2) If not, is there any way I could connect a USB drive in recovery mode, so I can retrieve some local files before wiping the disk for a complete re-install?
This was a problem solved by simple patience.

I left the machine with "2 minutes remaining" on overnight. After some period of time (presumably greater than 2 hours), the Yosemite install got over whatever was blocking it and completed.

I do not know what the fault was. I am assuming some simple but non-critical I/O was timing out, perhaps repeatedly in a re-try loop. Whatever it was, the predicted time was not updated to reflect the problem, making it look like the upgrade had hung.

That does make this a rather uninteresting fault in terms of Q&amp;A, but I am leaving this here in case anyone else ends up with a similar long-running upgrade and wonders how long to wait.

According to comment by klanomath, many developers (with a large number of project files/ruby/etc) experienced the same problem upgrading to Yosemite. I have just shy of 100,000 files in dev projects in my home folder.



It might be interesting to know if there is a way to back out of incomplete installations (without a disk wipe and re-install) at the late stage my machine was at. My original question is essentially about that. However, I won't be in a position to try or verify any answers.