We recently had some reports about Macs freeze on booting. The computers are all running the latest Yosemite. Here are the possible fixes for this problem. I listed them here with the detailed instructions on Apple’s website.
On most machines, you only need to reset the NVRam. There is one machine that I used all three methods to get it to boot normally. Note that these are also the general procedures when you have problems with booting a Mac. You can try them even if the machine is not running Yosemite.
You could try to delete BootCache.playlist file if all else fails.
- Press (Command+S) when the machine boots up to enter single user mode.
- Enter the following
/sbin/mount -uw / rm -rf /System/Library/Caches/* rm /private/var/db/BootCache.playlist reboot