These instructions apply only to Mac computers with an Intel processor.
Erasing your Mac permanently deletes all of its files, so make sure that you make a backup of any files that you want to keep. If you're attempting to restore your Mac to factory settings, first learn what to do before you sell, give away, or trade in your Mac.
Start up from macOS Recovery
Turn on your Mac, then immediately press and hold these two keys until you see an Apple logo or other image: Command (⌘) and R. You may then be asked to select a user you know the password for. Select the user, then click Next and enter their administrator password.
Use Disk Utility to erase your disk
- From the utilities window in macOS Recovery, select Disk Utility and click Continue.
- Select Macintosh HD in the sidebar of Disk Utility. Don't see Macintosh HD?
- Click the Erase button in the toolbar, then enter the requested details:
- Name: Continue to use Macintosh HD as the name, or enter a different name.
- Format: Continue to use APFS or Mac OS Extended (Journaled), as recommended by Disk Utility.
- Click Erase Volume Group. If you don't see this button, click Erase instead.
- If Find My is turned on for this Mac, you may be asked to enter your Apple ID to authorize the erase. Forgot your Apple ID?
- After the erase is done, select any other internal volumes that may be listed in the sidebar, then click the delete volume (–) button in the toolbar to delete each volume.
You don't need to delete the Macintosh HD volume you just erased, or any external volumes or disk images. - Quit Disk Utility to return to the utilities window.
- If you want to start up again from the disk you erased, you should now reinstall macOS on that disk.
How to format usb flash on mac or how to format hard disk on mac with best free usb drive formatting software download for mac or HP USB Disk Storage Format Tool mac edition download and free hard disk format tool mac to format usb flash drive fat32 on mac os or to create bootable usb or format usb in mac. Way 1: Boot Mac from USB Drive using Startup Manager Getting your Mac to load from a USB drive is fairly straightforward. 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. Select the USB flash drive in Disk Utility. Click the 'Partition' tab, if you want to use more than one partition in the drive. A drive with two partitions, for example can have one partitioned in ExFAT and another in a Mac OS Extended format, so you can use the same drive on a.
If you don’t see Macintosh HD in Disk Utility
Your built-in startup disk should be the first item listed in the Disk Utility sidebar. It's named Macintosh HD, unless you changed its name. If you don't see it there, choose Apple menu > Shut Down, then unplug all nonessential devices from your Mac and try again.
If your disk still doesn't appear in Disk Utility, or Disk Utility reports that the erase process failed, your Mac might need service. If you need help, please contact Apple Support.
Learn more
For more information about using Disk Utility, see the Disk Utility User Guide.
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. For example, if you install macOS or Microsoft Windows on a USB drive, your Mac can recognize that drive as a startup disk. This guide provides 2 ways to boot a Mac from a USB flash drive.
Requirement
Starting up your Mac from an external disk requires the following:
- Intel-based Mac.
- Bootable USB thumb drive formatted with a GUID partition type and containing an OS X installer or a usable operating system.
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.
Way 1: Boot Mac from USB Drive using Startup Manager
Getting your Mac to load from a USB drive is fairly straightforward. 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.
Step 1: Insert the USB boot media into a USB slot.
Step 2: Turn on your Mac (or Restart your Mac if it’s already on).
Step 3: Press and hold the Option key immediately after you see the Apple logo. Holding that key gives you access to OS X’s Startup Manager. Once the Startup Manager screen appears, release the Option key. The utility will look for any available drives that include bootable content.
Step 4: Using either the pointer or arrow keys on the keyboard, select the USB drive you wish to boot from. Once selected, either hit the Return key or double-click your selection. The machine will start to boot from the USB drive.
Way 2: Set a Mac Boot from USB Drive using Startup Disk
When you use Startup Disk preferences to set Mac boot from an external drive, so it’ll boot from that disk until you choose a different one. Here is how:
Step 1: Go to Apple menu > System Preference, then click Startup Disk.
Step 2: Click the locked icon and then enter your administrator password.
Step 3: Select External drive as the startup disk, then restart your Mac.
What to do if your Mac does not boot from the selected drive
If you see a message prompts that your security settings do not allow this Mac to use an external startup disk, check the External Boot setting in Startup Security Utility, and then allow your Mac to use an external startup disk.
Step 1: Open Startup Security Utility.
Turn on your Mac, then press and hold Command (⌘) + R immediately after you see the Apple logo. Your Mac starts up from macOS Recovery. When you see the macOS utility window, choose Utilities > Startup Security Utility from the menu bar. When you’re asked to authenticate, click Enter macOS Password, then choose an administrator account and enter its password.
Step 2: Select “Allow booting from external media“.
If you want to select an external startup disk before restarting your Mac, quit Startup Security Utility, then choose Apple menu > Startup Disk.
Note: If you’re using Boot Camp in a dual-boot Windows/OS X environment, you may be unable to boot negatively into supported versions of Microsoft Windows XP, Windows Vista or Windows 10 operating systems installed on external USB hard drive.
Make sure disk has been formatted with a GUID partition type
Intel-based Macs support starting from an external USB storage device’s volume that has been formatted with a GUID partition type. If you wish to boot from the drive, it’s important to format the partition as “GUID Partition Table” rather than either of the other two ahead of time when you use that drive as a bootable drive.
Make sure your disk is bootable
Format Usb Disk Drive
Volumes that aren’t bootable and don’t contain a copy of a valid operating system aren’t listed in Startup Disk or Startup Manager. Make sure the external drive you’re trying to start from contains a usable operating system.