How To Create a Bootable Yosemite Thumb Drive

In most cases, upgrading to OS X Yosemite from an older version of OS X is simple. Just launch the Apple App Store, download the upgrade, and install it. In some cases, however, it may be necessary to install a fresh copy of Yosemite by booting from an external thumb drive. The following instructions will walk you through step-by-step on how to make your very own Yosemite bootable thumb drive.

If you follow the steps exactly as outlined, total time to completion is 20-30 minutes. This includes everything you need to create a clean, bootable thumb drive AND proper clean-up afterwards.

What you need

  • USB Thumb Drive (8 GB or larger)
  • OS X 10.10 Yosemite installer file

Step 1) Download OS X 10.9 Mavericks

  • Open the App Store and begin downloading OS X 10.10 Yosemite (direct link)
  • When the download has completed, DO NOT INSTALL
  • Open Finder then click on "Applications"
  • Right-click on the "Install Mac OS X Yosemite" app and choose "Show Package Contents"
  • Browse to Contents/SharedSupport
  • Right-click on the file called "InstallESD.dmg" and choose "Copy"
  • Right-click on your Desktop and choose "Paste" to put a copy of the file on your Desktop

Step 2) Prepare the thumb drive

  • Insert your thumb drive
  • Open Disk Utility (Applications > Utilities)
  • Highlight the thumb drive on the left side of Disk Utility
  • Click the "Partitions" tab
  • Warning: the following steps will erase all contents on your thumb drive
  • From the "Partitions Layout" drop-down menu, select "1 Partition"
  • From the "Format" drop-down menu, select "Mac OS Extended (Journaled)"
  • Click on "Options..."
  • Choose the "GUID Partition Table" option, then click "OK"
  • Click "Apply"
  • Confirm the change to continue by clicking "Partition"
  • Quit Disk Utility 

Step 3) Enable "Show Hidden Files" 

  • Open "Terminal" (Applications > Utilities)
  • Type "defaults write AppleShowAllFiles TRUE" <enter>
  • Quit "Terminal"

Step 4) Mount the installer

  • Double-click on the "InstallESD.dmg" file (on your Desktop)
  • Notice the file called "BaseSystem.dmg"  (grayed out)
  • Move the resulting Finder window to one side of your screen
  • Open Disk Utility and drag it to the opposite side of your screen so you can see both windows
  • Highlight your thumb drive on the left side of Disk Utility
  • Click not he "Restore" tab
  • Drag the "BaseSystem.dmg" file from the "InstallESD.dmg" Finder window to the "Source" field in Disk Utility
  • Drag the thumb drive partition "Untitled 1" on the left side of Disk Utility to the "Destination" field in Disk Utility
  • Click "Restore" then "Erase" (this process will take 5-10 minutes)
  • Quit Disk Utility and close all Finder windows

Step 5) Copy the Installer Packages

  • Double-click on the "InstallESD.dmg" file (on your Desktop)
  • Right-click on the folder called "Packages" and choose "Copy"
  • On the left side of the Finder window, select your thumb drive now called "OS X Base System"
  • Browse to System/Installation
  • Delete the alias called "Packages"
  • Right click in the white space in the same directory and choose "Paste" (this will paste the "Packages" folder from "InstallESD.dmg" to the thumb drive
  • After the copy finishes (this will take 15-20 minutes), close all Finder windows

Step 6) Disable "Show Hidden Files" in Finder

  • Open "Terminal" (Applications > Utilities)
  • Type "defaults write AppleShowAllFiles FALSE" <enter>
  • Quit "Terminal"

When all steps are completed, you are welcome to either continue with the upgrade to OS X Yosemite on your Mac if you haven't already, or cancel the install and delete the "Install OS X Yosemite" app in Applications. You now have a bootable thumb drive with OS X Yosemite.


Posted on October 17, 2014 and filed under How To, Mac.