Once the Startup Manager screen appears, release the Option key. Holding that key gives you access to OS X’s Startup Manager. Press and hold the Option key immediately after you see the Apple logo. Turn on your Mac (or Restart your Mac if it’s already on).ģ. Insert the USB boot media into a USB slot.Ģ. Use the following steps, you can easily set Mac boot from an external drive in Startup Manager, so it’ll only boot from USB that one time.ġ. Getting your Mac to load from a USB drive is fairly straightforward. Way 1: Boot Mac from USB flash drive using Startup Manager Let’s see how to boot a Mac from a bootable USB drive and what to do if your Mac doesn’t start up from it. Bootable USB thumb drive formatted with a GUID partition type and containing an OS X installer or a usable operating system.Starting up your Mac from an external disk requires the following: This guide provides 2 ways to boot a Mac from a USB flash drive. For example, if you install macOS or Microsoft Windows on a USB drive, your Mac can recognize that drive as a startup disk. You can now quit Terminal and eject the volume.By default, Mac starts from its built-in hard disk, but a startup disk can be any storage device that contains bootable contents that compatible with your Mac. When Terminal says that it's done, the volume will have the same name as the installer you downloaded, such as Install macOS Monterey.After the volume is erased, you may see an alert that Terminal would like to access files on a removable volume.Terminal shows the progress as the volume is 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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