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Create Yosemite USB-drive Installer

Posted in: geeky    

Update October 19, 2014

With the release version of OS X 10.10, createinstallmedia finally works. You can follow the same procedure as when creating the USB installer for OS X 10.9 – just update the Terminal command to reflect the downloaded Yosemite Installer. If you prefer the GUI approach, have a look at DiskMaker X. I won’t cover DiskMaker X here.

The short version

  1. USB-media. A USB-stick, 8GB or more. Format the media as Mac OS X Extended (Journaled) with GUID partition mapping. Name it Untitled
  2. Download the Yosemite Installer for the App Store. It launches after the download is finished, but just quit the installer.
  3. Use Terminal (/Applications/Utilities/Terminal) to create the USB-installer

In Terminal, enter:

$ sudo /Applications/Install\ OS\ X\ --volume /Volumes/Untitled --applicationpath /Applications/Install\ OS\ X\ --nointeraction

Type in your administrative password.

Wait 15-20 minutes for the process to finish. You can now boot from the newly created USB installer holding down the option-key during startup.

Tip for Homebrew users (and others with a lot of content in /usr/local)

If you have lots of non-Apple files in /usr, the Yosemite upgrade might take may hours. Use this tip from Jim Lindley on moving the content in /usr/local before upgrading.

End update 2014-10-19

In OS X 10.9 Mavericks, Apple introduced a new way of creating a USB installer with the createinstallmedia executable.

The executable is present also in OS X 10.10 Yosemite Developer Preview, but there seems to be a bug which prevents the process to carry through.

In the meantime you can create a Yosemite boot stick much in the same way as early Maverics builds worked.

Mount the InstallESD.dmg image that’s under the installer /Contents/SharedSupport.

Mount BaseSystem.dmg using the Terminal

$ open "/Volumes/OS X Install ESD/BaseSystem.dmg"

Using Disk Utility, Restore the “OS X Base System” volume to your USB stick.

Not necessary, but to make things easier, rename the USB stick something else. I use “yosemiteDP1”

On the USB stick, in the folder System/Installation, delete the symlink named “Packages”

Copy the “Packages” folder from “OS X Install ESD” to the System/Installation folder on your USB stick.

Using Terminal, copy BaseSystem.dmg and BaseSystem.chunklist (they are both hidden from the Finder) from OS X Install ESD to your USB stick

$ cp "/Volumes/OS X Install ESD/BaseSystem.* /Volumes/yosemiteDP1"

Unmount the stick, boot away.

Let’s hope this bug is fixed before Yosemite DP2

Update I 2014-07-08: Still broken in DP3

Update II 2014-07-08: The new installer downloaded from App Store is still DP1, so I can’t verify the statement in Update I.