How to Create a Bootable Installer for macOS

A bootable macOS (previously, OS X) install disk is a portable device containing all the necessary installation files for a selected version of macOS. Why would you want to create an external boot drive for your Mac?

Such a tool allows you to install any version of macOS on multiple Apple computers easily. You can also use it to reinstall the operating system on a Mac that won’t startup. It’s a handy appliance—even more so if you use a small external flash drive that you can carry in a pocket.

Before we start:

We’ve written this guide to make creating a bootable installer as easy as possible. However, things don’t always go to plan, and you may need some extra help to get the job done. In that case, we recommend trying MacKeeper’s Premium Services. This puts you in touch with our team of technical experts, available 24/7.

This is how to access Premium Services in MacKeeper:

1. After you download MacKeeper, run it and select Premium Services from the left.
2. Click the Chat Now button.
3. A new window will appear on the right, and you’ll connect with one of our experts.

Make sure to check out MacKeeper’s other features too. It can do everything from finding malware to updating your apps, and you can try out the different tools for free.

What is a bootable installer for macOS?

A bootable installer is an external disk that contains the full set of installation files and drivers required to install an operating system on a computer. Typically, this is done using some kind of USB-connected drive.  

If you create a bootable installer for a Mac, it will be a way for you to install macOS. You might do it this way if you want to downgrade to an earlier version or if you need to do a clean install because macOS is corrupted or infected by malware. A bootable installer can be useful for updating multiple Macs too, because you won’t need to keep downloading the installer.  

What do you need to make a bootable USB on Mac?

Making a bootable USB drive for Mac isn’t too difficult, but you can save some time by having what you need ready in advance. We’ll go into everything in detail in just a moment, but this is essentially what you’ll need to make your bootable USB:

1. A suitable USB-connected external disk. This could be a hard drive or a solid-state drive, but we prefer to use a pen drive.
2. The macOS installer files from Apple. These vary in size depending on which version of macOS you’re installing, so be sure to check your USB is big enough for your intended operating system. Older versions of macOS will come as a Disk Image (DMG) file.

You’ll also need free space on your Mac to download the installer files, and your USB drive must have enough capacity for the installation process.

Get a bootable flash drive

For your external disk to run macOS, you can use most external USB drives, including solid-state drives and traditional hard drives. Generally, though, USB flash drives are favored  —  they’re small, convenient, affordable, and easy to work with.

It’s important to use a drive with enough capacity to fit macOS. Ventura’s installer is over 12GB, as was Montereys, and Big Sur’s topped 13GB. That means you’ll need to grab yourself a 16GB or larger flash drive before you get started.  

Bear in mind — when you download an installer, the disk will be reformatted to suit the operating system you’re trying to run. Give your disk the name of the operating system, e.g., Ventura, Monterey, Big Sur.

In the following instructions, we will use a USB flash drive as an external carrier example.

Get macOS installation files

You might want to keep installing files on an external drive if you think you might need to install the operating system multiple times or on different computers.  If, however, you only want to reinstall macOS once on one computer, you don’t have to use a carrier. In this case, the system will be installed on that Mac, and the installation files will disappear when the process is finished.

If you have the right installer, you can create a bootable installer for any operating system. The easiest way to get a macOS installer is from the App Store, which currently offers versions of macOS from High Sierra and later.

If you want an older version of macOS or OS X, then you’ll need to go to Apple’s official website. From there, you can get direct links to DMG files for Lion, Mountain Lion, Yosemite, El Capitan, and Sierra.

Here’s how to get a macOS installer from the App Store:

1. Open the App Store and search for the version of macOS you want. Click View.
2. Click Get. Your Mac will now download the installer.
3. The installer will be downloaded to your Applications folder. 

Prepare bootable USB drive with Mac Disk Utility

Now that you have the installation files ready on your Mac, you can move them to your USB drive for future use.

To install macOS on an external hard drive:

1. Connect the USB to your MacBook, then open Disk Utility by following Applications > Utilities > Disk Utility.
2. In the sidebar on the left, click on your disk name. Before formatting the disk, make sure it’s backed up. Click on Erase.
3. Choose OS X Extended (Journaled) for format and GUID Partition Map for scheme. Click Erase.
4. When Disk Utility is finished, click Done.

Now your flash drive runs the version of macOS that you want. You can run this OS when you connect the disk to your Mac—the Mac itself will keep its operating system.

Use Terminal to create a bootable installer

Another way to create a bootable installer for macOS is to use Terminal. Make sure that you have the installation files on your Mac before trying this step out.

How to make a bootable USB on Mac:

1. Open Terminal by following Applications → Utilities → Terminal.
2. Connect the USB drive to your Mac.
3. Type in: 
   sudo /Applications/Install\ macOS\ Sequoia.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume—if you want to install macOS Sequoia. MyVolume is the name of your external drive
4. Click Enter and type in your password.
5. You’ll see a warning about the disk being erased—confirm the action. Bear in mind that your external drive will be reformatted, and all data will be deleted from it

At the end of the process, you’ll receive a notification. You can now quit Terminal, eject your flash drive and use it for other installations.

If you simply want to upgrade to Catalina from an older version of macOS, the steps are much more straightforward — simply search for the name of the OS in the App Store and click Get to download the installation files, and start the process on your computer.

Boot your Mac from a USB drive

Having made your flash drive bootable, you can use it on many different devices to install macOS. How you do that depends on whether your Mac is based on an Intel processor or Apple Silicon.

How to use a bootable USB installer on an Intel Mac:

1. Turn off your Mac, making sure it’s connected to the internet.
2. Plug in your USB drive.
3. Now turn on your Mac, and immediately hold down Opt.
4. When you see a screen listing your bootable volumes, release the Opt key.
5. Select your USB drive, and press Return.
6. Choose your language, then select Install macOS.
7. Click Continue, and follow the on-screen instructions.

If you’re unable to boot from the drive, you might have a Mac with an Apple T2 Security Chip. In that case, you’ll need to change your security to enable booting from USB:

1. Turn your Mac off, then turn it back on while holding down Cmd + R until the Apple logo appears.
2. Enter your login details, then select Utility > Startup Security Utility from the menu bar.
3. Enter your password.
4. Now, under Allowed Boot Media, select Allow booting from external or removable media.

To use your bootable USB drive on an Apple Silicon Mac, follow these instructions:

1. Turn off your Mac, making sure it’s connected to the internet.
2. Plus in your bootable USB drive, then turn on your Mac, holding down the power button until you see your startup options.
3. Select your USB drive, then click Continue.
4. The macOS installer will start, then you just need to follow the on-screen instructions.

Again, Apple’s security features can prevent USB drives from booting. If your Mac uses an Apple processor, follow these steps:

1. Turn off your Mac, then turn it back on, holding the power button down until you see your startup options.
2. Click Options > Continue.
3. Select an admin account, and enter the password.
4. Now, from the Recovery tool, select Utility > Startup Security Utility from the menu bar.
5. Switch from Full Security to Reduced Security (it’s a good idea to change this back later).

Don’t forget to back up your files

As mentioned before, reinstalling macOS and reformatting disks will erase information from the drive. You’ll need to create a backup. You can use an external carrier to back up your Mac with Time Machine—a default app for Macs that allows storing your important data.

FAQ

How to create a bootable macOS Ventura installer drive?

To create a bootable drive for Ventura, follow these steps:  

1. Download the installer from the Mac App Store.
2. Plus in your USB drive, then open Terminal from Applications > Utilities > Terminal.
3. Enter the following, making sure your installer is in the Applications folder. Also, change MyVolume to the name of your USB drive:
   
   sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
    
4. Press Return, then enter in your admin password.
5. When asked, press Y to confirm that you want to erase the USB drive.
6. When it’s done, Terminal will ask to access the files on a removable drive. Click OK.
7. Terminal will now create the bootable drive. When it’s finished, you can quit Terminal and eject the drive.

The process for earlier versions of macOS is almost identical for earlier versions of macOS, but with slightly different Terminal commands. You can find out more in Apple’s official guidance. Note, however, this only goes as far back as El Capitan.

How do I make a bootable Yosemite installer?

Apple’s instructions on creating bootable drives only stretches as far back as El Capitan. If you have a very old Mac, you might not be able to install El Capitan or newer. For example, OS X Yosemite can be installed on older models of MacBooks but nothing newer. To create a bootable installer for Yosemite, you’ll need a flash drive with a minimum of 8GB of free space. The easiest way to turn a drive into an installer is through Terminal, but you have to reformat it and name it Untitled:

1. Download the Yosemite DMG file from the Apple website.
2. Make sure your Yosemite installer is in your Applications folder, and rename your USB drive to Untitled.
3. Open Terminal, and copy in this command:
   
   sudo /Applications/Install OS X Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install OS X Yosemite.app --nointeraction
    
4. Press Return, then enter your admin, and press Return again.
5. This will erase your USB drive and install the Yosemite files.
6. When it’s done, you’ll have a bootable Yosemite USB drive.

Can I use Rufus on Mac?

Rufus is an app that lets the user create bootable drives. Unfortunately, there’s no current version of macOS that you can use Rufus on.

Read more:

• How to Make a Bootable High Sierra Installer
• How to Back Up Your Mac
• What to Do if Your Startup Disk Is Full
• Step-by-step Guide to Reset Mac to Factory Settings