Each operating system could crash at one time or another. While it's safe to say that macOS is more stable than Windows, it can still be affected by issues that prevent your computer from booting up. In such cases, you might need to boot your Mac from a USB flash drive to fix the problem. This article shows you two ways to boot Mac from external USB stick, as well as some troubleshooting tips in case Mac won't boot from the target USB.
Boot Mac from USB Option l: Startup Manager
If your Mac won't boot up normally, you can set it to boot from a different drive, such as a USB stick containing macOS installation files in bootable format. The drive will have to contain a version of the OS that is compatible with the Mac. As long as you have the bootable installation USB, you can start your Mac from the USB by accessing the Startup Manager. Here are the steps to be followed:
Start up the Mac, holding down the Option/Alt key while it is booting up. Your Mac will display the Startup Manager, click on your external drive to select that as the startup disk. Double-click or press the Return key to start up your Mac from the volume you selected. If you have an optical drive connected to your computer, you can insert an installation disc to see it in Startup Manager. You can also attach FireWire or USB external hard drives that contain an operating system to add to the list of startup volumes. In this video walkthrough, I show you step-by-step how to deploy a Windows installation using Boot Camp drivers on an external drive connected to your Mac. Be sure to subscribe to 9to5Mac on. How to boot macOS Big Sur on an M1 Mac from an external bootable drive With the Mac powered off, connect the external bootable drive to the Thunderbolt 3 port.
Step 1: Insert the bootable USB into Mac and power it on.
Bootable optical media (CD or DVD) on Macs equipped with Apple's Super Drive or a USB thumb drive formatted with a GUID partition type and containing a macOS installer or a usable operating system. Apple advises against booting from external storage containing a version of macOS earlier than the one your Mac shipped with.
How To Boot Mac From Hard Drive
Step 2: As soon as the startup process begins, hold down the Option (alt) key and keep it depressed until you see the Startup Manager on your screen. If there is a firmware password on your Mac, hold down the Option key until you're asked to enter that password.
Boot From External Hard Drive
Step 3: You will now see the various startup disk options, and your USB will be listed there. If you click on the Up arrow right below the icon for the USB, the computer will only startup once using this disk. If you press and hold down the Control key while making your selection, it will be saved, and your computer will boot from the USB every time, as long as it is left in the computer.
At this point, you can also use the Mac installation disk to boot your Mac from. It will appear as EFI Boot, and it works on all computers running macOS 10.9 or higher.
Boot Mac from USB Option 2: macOS Recovery Mode
As an alternative, you can start your Mac in Recovery Mode. This will allow the system to automatically detect and repair directory issues. Recovery Mode will only allow required kernel extensions to load, preventing login items and startup items to load automatically. It can also help you isolate the issue depending on whether or not the issue goes away in Recovery Mode. If the issues you have during normal startup don't show up in Recovery Mode, they are most likely fixed. That means you can reboot normally and your system should be back to normal.
Step 1: Start your Mac and hold down the Shift key. You will see the Apple logo on your screen.
Step 2: When you see the login screen, you can release the Shift key and login to your Mac.
Step 3: To check whether your Mac has booted into Recovery Mode, click on the Apple logo on the top left and then on About this Mac. In the window that opens, click on System Report… You should be able to see this:
How to Fix Mac Won't Boot from USB Drive
Sometimes Mac won't boot from USB as expected. If you are unable to select a different startup disk, it's possible that your disk is not showing up in Startup Manager. If you try Method 1 above but don't see your USB drive listed there, it could mean one of the following problems:
Compatibility: It is possible that the version of macOS or Mac OS X that you have on the USB drive is not compatible with the hardware. That means you won't be able to see it in the Startup Manager so, of course, you won't be able to boot from it. In such cases, you may need to burn a compatible macOS version on USB drive in order to be able to boot Mac from it.
Startup Security Utility: In certain cases where your Mac has the Apple T2 Security Chip (2018 and later devices), it may be your Startup Security Utility settings that are preventing you from booting from USB. In this situation, restart your Mac and hold down the Command + R keys when you see the Apple logo. This will put your Mac into Recovery mode. In macOS Utilities, go to Utilities >Startup Security Utility and sign in as admin. Under External Boot, select the second option - Allow Booting from External Media.
How to Fix Mac Won't Boot from USB Drive
Sometimes Mac won't boot from USB as expected. If you are unable to select a different startup disk, it's possible that your disk is not showing up in Startup Manager. If you try Method 1 above but don't see your USB drive listed there, it could mean one of the following problems:
Compatibility: It is possible that the version of macOS or Mac OS X that you have on the USB drive is not compatible with the hardware. That means you won't be able to see it in the Startup Manager so, of course, you won't be able to boot from it. In such cases, you may need to burn a compatible macOS version on USB drive in order to be able to boot Mac from it.
Startup Security Utility: In certain cases where your Mac has the Apple T2 Security Chip (2018 and later devices), it may be your Startup Security Utility settings that are preventing you from booting from USB. In this situation, restart your Mac and hold down the Command + R keys when you see the Apple logo. This will put your Mac into Recovery mode. In macOS Utilities, go to Utilities >Startup Security Utility and sign in as admin. Under External Boot, select the second option - Allow Booting from External Media.
Option ROM Firmware: Another known issue is that Option ROM firmware will not load in Startup Manager until you press certain keys manually. To do this, use Method 1 to access Startup Manager. Once you are there, press Option-Shift-Command-Period. You should now be able to see the USB drive. This is not exactly a problem as much as a feature. If the USB contains Option ROM firmware, you will need to press those keys everytime to boot from your pen drive.
These two methods and the troubleshooting tips should allow you to boot from USB or in Recovery Mode so you can then isolate the problem that's preventing your Mac from booting up normally.
Here are some solutions for accessing the files on your Macintosh Hard Drive when your drive will not boot to the desktop.
A Mac can be started via a USB port, with a USB key or external hard drive, but that device needs to have Mac OSX system installed on it to boot, as well as other requirements. Best bet is to always backup your Mac hard drive with a bootable image created by Apple Disk Utility or a third party utility such as Carbon Copy Cloner. The easiest way to keep your files backed-up is by using Time Machine, which is built in to the Apple OS. The only requirement for Time Machine is to have an attached hard drive to back your files up to.
If you don't have a bootable backup, or a way to get a Mac drive, you will need to boot the computer from another operating system.
First, try to boot your Mac in Recovery mode, holding down Cmd-r on restart. If that doesn't work, try for Internet Recovery, which is restart and hold down Cmd-Opt-R.
Apple OSX Internet Recovery Article: https://support.apple.com/en-gb/HT201314
Coding on mac. Secondly, you can try to boot your Mac into Safe mode to see if you can boot to a minimal desktop.
Start or restart your Mac. Immediately after you hear the startup sound, press and hold the Shift key.
Release the Shift key when you see the Apple logo appear on the screen.
After the Apple logo appears, it might take longer than usual to reach the login screen or your desktop. How to save docx as pdf on mac. This is because your Mac performs a directory check of your startup disk as part of safe mode.
To leave safe mode, restart your computer without pressing any keys during startup.
Apple Article on booting your Mac into Safe Mode: https://support.apple.com/en-us/HT201262
If neither of those work, find another Mac, connect it to your Mac with Firewire or Thunderbolt cable. Then reboot the non-bootable Mac holding down the 't' key, which puts it in Target Disk Mode. If this works, the Mac hard drive will appear as a mounted drive on the other Mac.
Apple Article on installing OSX on an External Hard Drive so you can boot from it: https://support.apple.com/en-gb/HT202796
Apple Article for creating a bootable installer for OSX Yosemite (10.10) & OSX El Capitan (10.11): https://support.apple.com/en-gb/HT201372
Apple Article: Booting Into Target Disk Mode For File Transfer: https://support.apple.com/kb/PH10725?locale=en_US
Once you have booted from an external drive, and you can mount the you hard drive that was not booting, you can search the drive for files to recover, beginning with the files that are in the /Users/Home/ Directory.
Accessing Hard Drives That Have Been Encrypted Using File Vault
If the hard drive you are trying to recover data from has been encrypted with File Vault, and you don't know the login password, you will need to use a Recovery Key to login into the drive so you can access the data.
You can access the Recovery Key from the Caper JAMF Software Server on campus. Log into the JSS: https://casper.uiowa.edu:8443.
For the step by step process to retrieve a Recovery Key, see ITS Support article:http://its.uiowa.edu/support/article/104815
