When booting your Mac you should only need to supply your username and password once in order to log in. However, there may be times upon cold-booting your Mac where you enter your password at the login prompt, but after the system shows a gray boot screen as expected, it displays your login window again. This problem does not affect the functionality of your Mac, and is only a minor hiccup in how FileVault disk encryption is set up on your system.
FileVault encrypts your entire disk, including the operating system. When you turn on your Mac, a login screen look-a-like is presented that shows the usernames your system has authorized to unlock the disk. Since these are users on the system, once the disk is unlocked and OS X loads, the login credentials you provided will be passed to the OS so it automatically logs in and does not require you supply the same credentials twice.
The problem here is that these credentials are not being passed to the OS, so the system will first ask for your username and password to unlock the disk, and then do so again to log into the system.
This break in the login process may happen after upgrading your system, especially to Yosemite, where Apple converts your hard drive to a CoreStorage volume (a special volume-management setup that allows for encryption). As part of Yosemite’s setup, you are encouraged to enable FileVault, so this feature may have been enabled by you somewhat in passing. This problem may also have happened when restoring from a backup, reinstalling Yosemite, changing and modifying user accounts, among other core system modifications.
The first approach for fixing this issue requires you toggle your account’s administrator status, especially if you have multiple administrator accounts set up on your system (admin status in Yosemite automatically grants the ability to unlock your hard drive):
- Go to the Users & Groups system preferences
- Click the lock to authenticate
- Ensure an account other than yours is granted admin status
- Log into that account and demote your current account to Standard
- Reboot your system for these changes to take effect, if prompted
- Log into your second admin account and re-enable admin status for your main account
- Shut down your Mac, and then boot it up to test your login windows
Create a new user account and toggle this option to give it admin status. Then restart your system when prompted.
While this involves a few steps, it is overall the fastest option for addressing this issue. Once completed and if the login window only displays once, you can go back to the Users & Groups system preferences and remove any temporary administrative accounts you had to create for this process.
The second approach for this problem is to disable and re-enable FileVault completely, which will re-associate your administrative accounts to the disk encryption prompt, setting up your Mac to pass the supplied credentials to the operating system when it loads.
- Go to the Security & Privacy system preferences.
- Go to the FileVault tab
- Click the lock and supply admin credentials to unlock the preference pane
- Click the “Turn Off FileVault…” button
- Restart your Mac when prompted
Click this button to disable FileVault, followed by restarting. Re-enabling FileVault will associate your admin accounts to unlocking the disk.
The problem with this approach is it may take a while to both decrypt and then re-encrypt the system, but it is perhaps the more thorough method of addressing this issue. Overall, I recommend you try the first approach, and then the second one if the first does not work for you.