Simple Steps to Make Your Mac Boot from a Flash Drive

Easy-to-follow steps for booting a Mac from a USB drive

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Last Updated: August 11, 2025 Tested

CD/DVD drives are disappearing from computers, leaving USB storage as the only option when re-installing an operating system. The process is fairly painless and, if you have a bit of time and patience you can complete the task on a Mac.

Things You Should Know

Get your version of macOS from the App Store and create a backup of it on your desktop.
Right-click the file on your desktop and make a bootable USB drive.
Go to Package Contents in that file and go to "Disk Utility", then drag the "InstallESD.dmg" file in that package to Disk Utility.

Steps

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The latest versions of the Mac operating system are only available through the App Store.
Don't worry if you lose connection halfway through download, it will resume as soon as you are re-connected to the App Store.

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Under no condition should you work on the original installer file.
This is your ticket to creating a bootable copy of OSX Mountain Lion.
Drag the “InstallESD.dmg” file from installer folder into the white box on the left side of Disk Utility, and the disk image will be added.
“InstallESD.dmg” should already be present in the source tab.
Drag the drive you just added to Disk Utility from the source list in the top left of the app white space to the “Destination” path.
This can take some time so please be patient.
You now have a bootable USB disk drive with Mac OS X Mountain Lion installed and good to go!
You can now use this disk to verify/repair disk partitions, repair current installed OSX, upgrade to new OSX, or perform a clean install of existing or better OSX.

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Question

What button combination do I use to get the boot menu on a Mac G4?

OPJustin

Community Answer

Holding the "alt" (option) key should open Apple's native boot menu. That should list available drives to boot from.

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Once I get to Step 28 - then what? That's what I'm trying to figure out, and all the how-tos take you to that step and then end. What do I do?

Community Answer

That's just the OS utilities menu. If you restart, it should boot into the normal OS.

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Tips

There are some third party apps like "Lion Disk Maker" which specialize in creating bootable disk for Mac.

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Always insist on original software as supplied by Apple Inc. and downloaded from Mac App Store.

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Warnings

Always backup your system using Time Machine before installing any new OSX.

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Always keep a backup of your installer file before copying to USB/external drive.

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A bootable Mac disk will work on Mac Computers ONLY.

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Do not disconnect the USB drive in the middle of the entire process.

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