Problem: While trying to upgrade a Mac to Mac OS X 10.11 “El Capitan” (or older versions) after ~13 minutes, the blue bar is complete, and on top, it says: ‘Preparing to install. Your computer will restart automatically.’. Below the blue bar, it says ‘About a second remaining’.
But it looks like it’s stuck on this state, with the mouse on the spinning wheel mode, for over a full hour. What should you do?
Solution: The problem with the upgrade script is the timing only estimates how long it takes for Apple’s software to install. You can (and should always) open the log file while upgrading/installing and press Command-3 to show all logs, not just the errors.
You can see that during this “about a second” it’s really migrating user files and handling all the things you’ve brought to the Mac that isn’t part of the base system. Basically, let it run as long as you can stand – especially if the log file shows progress being made.
After the reboot the systems starts to install all files on the startvolume. That’s all folks!