This document describes how to enable or disable automatic login for Mac OS X.
Important Note: If the username is grayed out, you are unable to enable automatic login as your Mac requires manual login. This can be fixed:
If FileVault is turned on, manual login is required for all accounts. You can turn FileVault off.
If an account uses an iCloud password to log in, manual login is required for that account. You might also see the message “A user with an encrypted home folder can't log in automatically.” When changing the account password, you can choose not to use the iCloud password.