There are various ways to boot macOS. Aside from using the built-in startup option, you can also boot into Verbose, Safe, and Target Disk modes. In addition to this, macOS users also have an option of picking a disk to boot the operating system from. But let’s delve into something more specific. You’re about to find out how to boot your Mac up directly from external storage, specifically flash storage or a USB flash drive. If you are also using PC, learn how to create bootable flash drive for Windows PC.
Why You Need to Boot from External Drive?
There are many occasions you may have trouble with your Mac.
- Corrupted system files and Mac crashes unexpectedly.
- Mac runs very slow with sufficient storage.
- You have deleted some system files wrongly.
- You couldn’t login to your Mac.
- For troubleshooting purposes.
In most situations, booting from USB drive can help to fix the problems especially those related to your primary hard disk.
How to Create Bootable USB Drive for Mac?
Let’s begin with the obvious question here; what are the basic requirements for creating bootable USB for Mac?
- USB drive with sufficient storage space
- Access to a working and supported Mac
- Installer file for macOS version
If you are not able to login to your Mac, then you can use Time Machine backup disk. Otherwise, you should have another Mac for creating a bootable USB.
1. Get Your USB Drive
The macOS installer file is larger with approximate size of 6 to 10GB depending upon the version. Also the process needs sufficient storage space on your USB. So, ensure to have at least 32GB or greater storage space on your USB drive. Remember to copy and backup the USB since you need to delete the entire content for creating the bootable drive.
2. Format USB Flash Drive to Apple File System
First, plug in your USB drive. Press “Command +Spacebar” to access Spotlight Search, then type “Disk Utility”. You can view the current file system of the USB drive. In our example, we have FAT32 file system which is only compatible on Windows PC. Hence, we need to erase and format the USB to be compatible with your Mac.
Select your USB drive and click on the “Erase” button from the top tool bar in “Disk Utility” app. Choose the format as either APFS or Mac OS Extended. In most cases, your Mac will show the supported format by default and you don’t need to change it. On older Mac, you will see an additional scheme option, choose “GUID Partition Map”. Click on “Erase” button to continue further.
Disk Utility will delete all content on the USB and format it in the selected APFS or Mac OS Extended format.
3. Get macOS Installer File
In order to create a bootable USB drive for Mac, you need to download macOS installer file. Open App Store on your Mac and search for the “macOS”. This will show the latest macOS version and click “Get” button. Use these links to get other macOS versions which are not visible when you search – High Sierra, Mojave, Catalina, Big Sur or Monterey. Remember, the link ask your permission to open it in the App Store.
This will start downloading the installer file to your “Applications” folder.
4. Creating USB Installer with createinstallmedia Command
After downloading, the installer will automatically ask you to install macOS Mojave. Simply quit the installer without starting the installation process.
- At this point, ensure you have inserted the formatted USB drive, let’s say the name of the USB volume is “Boot Disk”.
- Also, make sure the downloaded macOS installer file is in “Applications” folder.
- Press “Command + Spacebar” and search for “terminal” to open Terminal app.
- Copy and paste the below command in Terminal and hit enter which uses the example of Mojave version.
sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Boot Disk
- If the OS name has two words like Big Sur, then the command will change like below:
sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/Boot Disk
- Note the “Boot Disk” is the volume name of USB, make sure to use your USB drive name in the command.
- You need to enter admin password to proceed further.
- Terminal will ask you to confirm erasing the volume, press Y and hit enter to confirm.
Ready to start.
To continue we need to erase the volume at /Volumes/Boot Disk.
If you wish to continue type (Y) then press return:
- Now the erase disk process will start to copy the installer file on the USB drive. After successful completion of the process, name of the USB drive will be changed similar to the installer file name like “Install macOS Mojave”.
Note that Apple discourages booting with an earlier macOS version than the version your device is shipped with.
5. Boot Mac from USB
Follow the below process to boot your Mac from bootable USB:
- Insert the bootable USB installer drive and go to “Apple Menu > Restart”.
- If you are using Intel based processor, when your Mac restarts, press and hold the Option key till you see the system scans and lists the drives that are connected and bootable.
- Note that you will only see volumes that include bootable file. If you only see “Macintosh HD” like below then the USB drive is not connected to your Mac or not created properly with the installer file.
- Select your Wi-Fi network name from the “Choose Network…” dropdown and enter the password to connect to internet. Remember, you need to have an internet connection for installing from USB as the installer needs to get updates for your Mac from Apple’s server.
- Double click on your USB that contains the macOS installer or highlight it and press the return key.
- You will see macOS Recovery app and choose “Install macOS” option from Utilities.
- It may take long time depending upon your Mac to start booting from USB.
Note: If you are using Apple silicon based processor, press and hold power button during restart till you see all bootable volumes. Select the bootable USB drive from the list and follow the steps on the screen to finish the process.
As simple as the process seems, it tells you a lot about your system. For example, if a USB flash drive that contains a bootable copy of macOS doesn’t show up on the startup, you may need to repair the disk permission. Also, remember to format the USB drive with a APFS or Mac OS Extended format. That said, now you know how to boot up your Mac from USB and troubleshoot possible issues with your device.