Boot your Mac and hold down ⌘-R (Command –R) to boot from the Mac’s Recovery HD partition. Update – June 11, 2013: As of Mac OS X 10.8.4, you will need to unlock the encrypted volume first, then you will be able to decrypt it. In the event that you find yourself in this place, or you’re about to be, here’s how you can unlock or decrypt your FileVault 2-encrypted drive using Disk Utility and the password of an account that’s authorized to log in at the FileVault 2 pre-boot login screen. You can now quit Terminal and eject the volume.Bad things happen and sometimes those bad things cause your FileVault 2-encrypted Mac to be unbootable. When Terminal says that it's finished, the volume will have the same name as the installer you've downloaded, such as Install macOS Monterey.After the volume has been erased, you may see an alert stating that Terminal would like to access files on a removable volume.

Terminal displays the progress as the volume is being erased. When prompted, type Y to confirm that you want to erase the volume, then press Return.Terminal doesn't show any characters as you type. When prompted, type your administrator password.

If the volume has a different name, replace MyVolume in the command with the name of your volume. Each command assumes that the installer is in your Applications folder and MyVolume is the name of the USB flash drive or other volume you're using.

Type or paste one of the commands below into Terminal, then press Return to enter the command.

Open Terminal, which is in the Utilities folder of your Applications folder.

Plug in the USB flash drive or other volume that you're using for the bootable installer.

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