Pro tip: How to create a bootable USB installer for OS X Yosemite

Jesus Vigo walks through the steps of creating a bootable USB installer for Apple's OS X Yosemite. 

On June 2, 2014, Apple announced the next iteration of its powerful, yet elegant OS X operating system. Continuing the naming trend, Yosemite was made available the same day as the WWDC event in the form of a Developer Preview beta for software developers to test their apps on the new platform.
 
What about the end-user? Must we really wait until later this year to try out Apple's latest OS? Maybe not. Those interested in testing Yosemite may sign up for the OS X Beta Program, which will allow them to test the new OS, if selected.
 
A word of caution, however, as beta software is just that. Largely untested and full of bugs, this may lead to conflicts with production systems. Additionally, certain applications may not work fully (or at all) until updates are made available. It you decide to install beta software, you should do so on a sanitized, secondary device that meets requirements to minimize issues. 
 
Before getting started, let's review the requirements for creating a bootable drive:

• 8 GB USB Flash Drive (or SD Card)
• OS X 10.10 DP1.app (installer downloaded from Apple's Mac Developer site)
• Apple computer with Mac App Store (10.6.8+)
• User Account with Administrative privileges

With that said, follow the steps below to create a bootable USB installer:
     1.  Insert the USB Flash Drive (or SD Card) into the Apple computer, and launch Disk         Utility.app from the Applications | Utilities folder.
     2.  Select the drive you wish to use from the device list and click the Partition tab.
     3.  Under Partition Layout, select 1 Partition from the drop-down menu.
     4.  Enter a name for the device, and select the format as Mac OS Extended (Journaled) from the drop-down list next to Format (Figure A).
          Figure A

 

     5.  Click the Options button to bring up the partition scheme menu.
     6.  Select the radio button next to GUID Partition Table, clicking OK to accept the change (Figure B).
          Figure B

 

     7.  Verify the changes to be made to the drive are correct, and then click Apply. A verification prompt will appear. Click Partition to execute the changes (Figure C).

          Figure C

 
     8.  Depending on the size of the drive, the changes typically take several minutes to process. Once completed, the removable drive will be prepped for OS X (Figure D).
          Figure D

 

     9.  Launch Terminal.app to enter a command that will unhide the hidden files needed to complete the next few steps. Enter the following command (Figure E):
          defaults write com.apple.finder AppleShowAllFiles 1 | KillAll Finder
          Figure E 

 

     10. Navigate to the location where the OS X 10.10. DP1.app file is saved. Right-click the installer and select Show Package Contents from the context menu (Figure F).
          Figure F

  

      11. Sort through the file hierarchy Contents | SharedSupport and mount the InstallESD.dmg file by double-clicking it (Figure G).

          Figure G

     
     12. With the contents of the InstallESD.dmg file visible, there are two files specifically that will be used to create the OS X installer to the removable drive: BaseSystem.dmg and the Packages folder (Figure H).
          Figure H 

 

     13. Switch back to Disk Utility.app to select the partition name created in step #2.
     14. Next, select the Restore tab and drag the partition from the device list to the Destination box. Also, drag the BaseSystem.dmg file from the finder window to the Source box (Figure I).
         Figure I

 

     15. Clicking the Restore button will prompt a confirmation message. Clicking Erase will initiate the process to install the files onto the drive. Additionally, Disk Utility will request administrative authorization to perform the task. Enter the administrative credentials and click OK to execute the commands (Figure K).
         Figure K

     16. The process can take several minutes to complete. However, by my experience, it is far shorter than what is stated by the progress bar (Figure L).
         Figure L

 

     17. Upon completing the file transfer, the drive will auto-mount in Finder. Navigate to the System | Installation directory where you will find an alias to the Packages folder. Delete the Packages alias by right-clicking the file and selecting Move to Trash from the context menu (Figure M).
         Figure M

 

     18. To replace the alias, copy the Packages folder from Step #9 to the Installation directory. Again, the transfer time will depend greatly on the age of the machine (Figure N).
         Figure N

     19. As a rule of thumb, unless specifically necessary to your daily functions on the computer, launch Terminal.app to enter the command to make the system files hidden again. While optional, it is generally not considered a good security measure to keep these files unhidden. Enter the following command (Figure O): 
          defaults write com.apple.finder AppleShowAllFiles 0 | KillAll Finder
         Figure O

 

With the transfer completed and the files safely hidden again, the removable drive is ready to perform a clean or upgrade installation of OS X Yosemite. The process is almost identical to the Mavericks USB installer article from last year.
 
To perform a clean install, simply insert your drive, power on the computer, and hold down the [option] key to access the boot selection menu. From there, select the USB drive partition, and follow the prompts to install OSX 10.10 on your Mac. If performing this as an upgrade, then launch the Install OS X 10.10 Developer Preview.app from the root of the newly created drive, following the prompts to install it from a live environment.
 
~ Jesus Vigo

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