Yosemite install? Press Command-L
I installed Yosemite on my Mac Pro a few months after it came out. The Mac Pro has three harddisks and may be extra complicated, which might explain what happened: Hours after the progress bar of the install said it would be finished in 3 minutes, nothing else happened. So I made THE biggest mistake in history: I rebooted in the middle of the install. I then tried to re-install three more times and each time it got stuck. I then had to re-format one of my harddisks and do a clean install. After that it took me three months to put all my stuff on that harddisk (which included LaTeX and other rather complicated software.) That was really depressing.
So you understand why I waited another year before installing Yosemite on my MacBook Pro. Yesterday was the day. The install got to “2 minutes left” this time, and it got stuck again. Boy, was I sorry I had fallen for the lure of progress again.
So I googled on my Mac Pro for a solution to this, and this time I got a fine answer: the install is actually working in the background; it is just the progress bar that is failing (and let me add: it is failing grossly). And there is a way for you to see what the install is doing: press Command-L.
I did. And a log came in view, showing all the minor steps the installation was going through. If only Apple had told this before I started the installation, nothing bad would have happened.