Macs Running Yosemite Freeze on Booting

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.

1. Reset NVRam.
2. Reset SMC.
3. Boot to Safe Mode and reboot again.

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.

[Update: 4/1/2015]

You could try to delete BootCache.playlist file if all else fails.

1. Press (Command+S) when the machine boots up to enter single user mode.
2. Enter the following

   /sbin/mount -uw /
   rm -rf /System/Library/Caches/*
   rm /private/var/db/BootCache.playlist
   reboot