Yosemite upgrade process stuck for hours - Cmd-L not working Today I started the upgrade of my Mid 2011 iMac 27 from Mavericks to Yosemite. Initially it got stuck at the end of the first part of the installation. I could however pull up the installation log using Command-L and so I could tell it was still doing something. Eventually it completed and rebooted. It then got into the Completing Installation phase with a similar progress screen. It's been at "Less than a minute remaining" for the past 4 hours and no sign of activity. I also can't pull up the installation log by pressing Command-L. I just hear the familiar error sound when I try that.

I do use Homebrew so there's probably a lot of stuff in /usr/local causing the installation to take a long time, but I figured that's what caused part 1 of the installation to take so long, but it doesn't explain why part 2 is taking even longer.

Mavericks was installed on an external SSD (Lacie Rugged series) connected through thunderbolt. I now read that some people are experiencing problems with 3rd party SSD drives in Yosemite (yeah, I know I should have checked that before starting the upgrade, but who would have known?).

I'm not sure what to do now: just power off the computer and see if it continues finalizing the installation process after I restart it? Or just wait until tomorrow morning and see if it's still stuck? Even though I have a time machine backup on an external drive I don't want to risk losing my data forcing me to do a restore. Any advice?
Alright so I waited it out only to come back this morning to see that it was still stuck. I've waited several more hours until 10 am this morning which comes down to a total wait of 18 hours. I went ahead and manually rebooted and it looks like the upgrade was completed successfully after all.

Please note that this is not me suggesting you should reboot if the installation seems stuck. In general you should just be patient and wait. In the first phase of the installation press Command-L to show the installation log and you can verify it's actually doing something. Note that it can take a while for the installation log to show up after pressing Command-L.
In the second phase if it gets stuck you can't view what it's doing so it's pretty much a gamble if you decide to reboot it when it seems to be stuck.

I rebooted with my external backup hard drive disconnected to make sure my backup stays intact when things turn sour after all.

I verfied the disk and the permissions with Disk Utility and some permissions were off so I've repaired those. I'm now in the process of fixing Apache, but I'm guessing that's because of the differences between Apache 2.2 and 2.4.