Q: Macbook boots twice every time it starts

Follow the instructions here >  OS X: When your computer spontaneously restarts or displays "Your computer restarted because of a problem".

I'm experiencing the exact same issue on a MacBook Pro (Retina, 15-inch, Late 2013) running Yosemite, 10.10.2. Every time it boots (warm or cold), it interrupts the boot process to reboot a second time. Only the first has the boot chime. No error messages of any kind appear during or after the boot process.

Exactly the same double password prompting after every start on my MBP Retina 15"/2014/Yosemite 10.10.2/2.8 GHz i7/16GB/1TB SSD/GT 750M/Yosemite

Coming from Windows I purchased the best Apple could provide and I'm more and more disappointed and frustrated from OS X and the hardware.

Found this one: http://www.reddit.com/r/mac/comments/2afahr/have_to_login_twice_for_macbook_pro/

Is FileVault enabled? If so, you have to login once to unlock the encrypted disc followed by your standard account login.

Edit: To check if FileVault is enabled open System Preferences -> Security & Privacy -> FileVault

Apparently my problem self resolved without having the slightest idea how but it doesn't asks twice for my pass anymore. I didn't disable the FileVault or changed anything else. No idea.

Start up in recovery Command R or Option R. Go to utilities and run a repair of your drive, also doing a permissions repair. Close out of utilities and restart. Hold down the Command/Option/P/R keys for three chimes and continue boot.

I had the same problem. I would face this every time on cold start, but not on sleep wake. and I would hear the chime twice as well. In any case, the problem is caused as a result of a combination of few things and how they work namely - admin user profile management, file vault encryption and yosemite updates.

I found this article.. and it gives you two ways to solve this problem, and its spot on!

http://www.macissues.com/2015/03/31/fix-double-login-prompts-on-your-mac/

Yosemite shows your username up top, next to the clock. If you upgraded to yosemite and did not reset your user permissions in some way, this normally might not be visible. For me, after I was done with the above procedure, it solved that and the overlapping clock text problem as well! Once you see this, its a sign that things have worked..

Hope this helps!