Installing or reinstalling operating systems has been a lot easier since Apple decided to stop shipping installation discs and offering them as downloadable files from the Mac App Store instead. While the option is no doubt more convenient than keeping physical copies of your Mac’s operating system around, though, keeping a backup copy of your operating system is still a good idea in case something happened to your computer and it refused to start. A good way to do this is by creating a bootable USB drive.

What is a Bootable USB Drive?

Whenever your Mac starts, it initiates what is called a boot process where it tries to load your operating system so that you can use your computer. By default, your Mac boots from your internal hard drive, but, if for one reason or another, your hard drive won’t boot, your Mac will ask you if you want to use a different drive instead. This is when you use a bootable USB drive.Bootable drives can be any type of storage device (USB drive, CD, DVD, external hard drive, etc) that contains a copy of your operating system. In case something happened to your Mac and you can’t get it to start, you just plug in your bootable USB drive (or any other drive), wait for your Mac to detect it, then instruct your Mac to use the bootable USB drive to load your operating system instead.

How Can I Make a Bootable USB Drive?

 To make a bootable USB drive, you need to format your USB drive first. This is especially important if your USB drive is manufactured by a third-party because a lot of the USB drives on the market are based on the NTFS file system which is the default for PCs running on Windows. While your Mac can open files based on the NTFS file system, you cannot save anything on it without the help of certain third-party apps.

*Important Note:

Formatting your USB drive will erase ALL of its contents, so make sure that you transfer your files to another storage device if you still have remaining ones on the USB drive that you want to make bootable. Also, you need at least 8GB of space to make a copy of your operating system on your USB drive.

To format your USB drive,

1. Connect your USB drive to your Mac.
2. Open “Spotlight.”
3. Type in “Disk Utility” in the search bar.
4. Double click on “Utilities.”
5. Select your USB drive from the list of devices (Be careful not to click the wrong drive by accident or you might end up losing important files)
6. Click on the “Erase” tab.
7. Assign a name to your USB drive, preferably something that does not contain any space as it will be important later.
8. In the “Format” field, select “MAC OS Extended (Journaled) if you will be using your USB Drive exclusively on your Mac.  If you intend to use it on both your Mac and a PC, select “MS-DOS FAT” instead.
9. In the “Scheme” field, select “GUID Partition Map” if you’re going to use your USB drive exclusively on your Mac. If you intend to use it on both your Mac and a PC, select “Master Boot Record” instead.
10. Click “Erase.”
11. Wait for the formatting of the USB drive to finish.
12. Click “Done.”
13. Close the Disk Utility window.

 

After you’ve formatted your USB drive, you may proceed with copying your Mac’s operating system to it.

To save a copy of your Mac’s operating system to your USB drive,

1. Go to the Mac App Store.
2. Download the latest version of your operating system.
3. Open your “Applications” folder.
4. Look for the installer of the operating system.
5. Drag and drop the installer to your USB drive.

 

After you’re done,

1. Go back to your “Applications” folder.
2. Click on “Utilities.”
3. Open “Terminal.”
4. Paste the following code inside the box.

 

• Sierra – sudo /Applications/Install\ macOS\ 10.13\ Beta.app/Contents/Resources/createinstallmedia –volume /Volumes/YourUSBDriveName –applicationpath /Applications/Install\ macOS\ 10.13\ Beta.app –nointeraction
• OS X El Capitan – sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia –volume /Volumes/YourUSBDriveName –applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app –nointeraction
• OS X Yosemite – sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia –volume /Volumes/YourUSBDriveName–applicationpath /Applications/Install\ OS\ X\ Yosemite.app –nointeraction
• OS X Mavericks – sudo /Applications/Install\ OS\ X\ Mavericks.app/Contents/Resources/createinstallmedia –volume /Volumes/YourUSBDriveName –applicationpath /Applications/Install\ OS\ X\ Mavericks.app –nointeraction

 

*Note:

The command is case sensitive, so make sure that you type your USB Drive’s name exactly as how it was originally written or you can just copy and paste it to the Terminal to make things easier. Also, the USB drive name must not contain any space, so if the name that you gave it earlier has one, make sure that you erase it first.

After you’ve copied the code to the Terminal,

1. Press the “Return” key.
2. Type in your Administrator name and password.
3. Press the “Return” key.
4. Wait while the Terminal is running the command.
5. Depending on the amount of files it is trying to copy, it may take anywhere from a few minutes to a couple of hours, so you might want to work on other tasks while waiting.
6. After the copying process is finished, a message that says “Done” will appear.

 

Your operating system has now been copied to your USB drive and you may start using it as an alternative bootable drive in case you needed to troubleshoot an issue, reinstall your operating system, or install your OS on another Mac.