What to Do If You Forget Your Mac’s Password
If you haven’t enabled FileVault disk encryption, there’s an easy password-reset tool you can access. If you have enabled FileVault disk encryption and are willing to abandon your encrypted files, you can just reinstall Mac OS X and start over again.
Reset Your Password Using Your Apple ID
This trick only works if you’ve associated your Mac account with an Apple ID. It will work if you haven’t set up FileVault disk encryption, or if you set up FileVault disk encryption and had Mac OS X store your recovery key in your iCloud account. This is the default option. If you enabled FileVault and didn’t store your recovery key with your iCloud account, it won’t work.
If you’ve forgotten your password, just try entering the wrong password three times at the sign-in screen. After three wrong answers, you’ll see a “If you forgot your password, you can reset it using your Apple ID” message. Click the button and enter your Apple ID details to reset your passwordl.
Enter Your FileVault Recovery Key
If you’ve enabled FileVault disk encryption and didn’t store your recovery key in your iCloud account, the FileVault setup tool gave you a recovery key and told you to print it out or write it down and store it somewhere safe. This — aside from the password — is the only thing that can decrypt the files stored on your Mac and give you access to them.
Assuming you have this recovery key, you can type the recovery key into the password field on the login screen. This will decrypt your Mac’s storage and sign in you in. Once you’re signed in, you can change the password from the usual Users & Groups tool in the System Settings window.
Reset the Password From OS X Recovery (If You’re Not Using FileVault Encryption)
If you haven’t enabled FileVault encryption, there’s an easy way to reset any user account’s password. You just need to restart your Mac and hold Command + R while it’s booting. This will boot your Mac into a special recovery mode, also known as OS X Recovery.
From OS X Recovery, you can access a hidden a password reset tool and use it to change any user account’s password on the Mac. This is another good reason why you should enable FileVault encryption on your Mac — it’ll prevent people from entering the password and gaining access.
In the unlikely event that you’ve enabled a UEFI firmware password on your Mac, you won’t be able to gain access to OS X Recovery unless you remember that password. You can’t remove that UEFI firmware password without visiting an Apple Store — at least in theory. This helps prevent thieves from just erasing the UEFI password of a MacBook after they steal it.
Sign In As Another User (If You Are Using FileVault Encryption)
If you have more than one user account on your Mac and are using FileVault encryption, try logging in as the other user account. If you gave that other user account permission to decrypt your Mac with its password, you’ll be able to sign in and access a desktop. You can then create a new user account or regain access to your old user account.
Reinstall Mac OS X (If You Are Using FileVault Encryption)
If there’s a UEFI password on your Mac, you won’t be able to gain access to OS X Recovery to reset the password or reinstall Mac OS X without that password. You’ll just see a big lock icon appear on your screen and a box to type your password when you try to boot into recovery mode or boot from an external device.
This is a separate password from your user account’s password, so hopefully you remember this one. If you can’t, the only way to potentially remove that UEFI password is to take your Mac to an Apple Store.
There may be some sort of attack that allows an attacker to bypass a UEFI password, but, in theory, only Apple can remove an unknown UEFI password.
If you can’t remember your Apple ID (iCloud) password, Apple’s website offers an Apple ID password reset tool that might be able to help.