Create a Bootable USB for Mac OS X (El Capitan 10.11 or Yosemite 10.10)

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OS X Yosemite

It’s Mac OS X season again and with that is a new version of Mac OS X. In this case it is Mac OS X 10.10, or what is better known as Yosemite. Most people will upgrade their Mac over the top of their existing OS, which is perfectly fine. However, there are times when OS X needs to be installed on a new (blank) hard drive, or, we simply want to perform a “clean install”. When doing this I prefer to use a bootable USB drive instead of a DVD. This is becoming especially convenient as newer Macs don’t have (or need) an internal DVD drive.

For reference, Apple has a page that covers how to create a bootable USB drive with the OS X 10.9 Mavericks installation files, but leaves out a few of the details discussed here. This should also provide is little context around this being a standard process that is supported by Apple. No hackery here.

What is needed

The process is easy and any Mac user who considers themselves to be semi-technical will be capable of creating a bootable USB drive containing the Mac OS X installation files. And, this does not require downloading any third-party tools or paying for extra utilities. Here is what you need.

  • A Mac with internet access
  • One 8 GB (or larger) USB drive
  • The OS X installation file from Apple (i.e.; “Install OS X Yosemite”)

Downloading the OS X installation file

To create a bootable USB drive for OS X, you first need to download the desired operating system setup file from Apple, such as OS X 10.10 Yosemite. You can search for the OS, “OS X Yosemite”, in the App Store (or using this link) to access it in the App Store directly. Once the download completes, you will see the OS X Install window for Yosemite (or other version), but do not proceed with the install; you need quit the install. You just needed the Install OS X Yosemite application, which should now be in the Applications folder on your computer. For Yosemite, the file name will be Yosemite.app.

Creating the bootable USB drive

Here is what you need to do:

  1. Connect the USB drive to your Mac. Backup any files that may be stored on it before you proceed because this USB drive will need to be completely reformatted.
  2. Format the USB drive, using Disk Utility, as a Mac OS Extended (Journaled) drive, named Yosemite. I suggest not using any spaces to keep a future step simple. This is performed using the Erase tab within the Disk Utility app. Be sure the USB drive does not have multiple partitions (that can happen, so use to the Partition tab to verify and correct this).
  3. Open Terminal. This located in the Applications > Utilities folder.
  4. The following command is used to make the USB drive bootable as well as copying the necessary OS installation files on the USB drive.A couple quick points to help make sense of the command below. The –volume /volume/YosemiteUSB attribute of the command specifies the target drive, the USB drive in this case. The –applicationpath attribute specifies the OS X source installation file that was downloaded earlier. You will also notice the command (createinstallmedia) used to create the installable USB drive is actually contained with Yosemite.app file that was downloaded.Type (paste) the following command

For Yosemite:

sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/YosemiteUSB --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
  • For El Capitan:
sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/ElCapitanUSB --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app
  1. To kick off the process, type in your user password when requested.

This process can take upwards of 30 minutes or more without any indication on the screen it is still processing. Even though it may appear to have locked up, put your worries aside and your patience will be rewarded. The time it takes will vary depending on the speed of your Mac and the USB drive write speed.

Sample log

Below is a log of the terminal screen from when I created my bootable USB drive containing the Yosemite OS X installation files.

Marks-MacBook-Pro:~ Mark$ sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia --volume /Volumes/Yosemite --applicationpath /Applications/Install\ OS\ X\ Yosemite.app
Ready to start.

To continue we need to erase the disk at /Volumes/Yosemite.
If you wish to continue type (Y) then press return: Y
Erasing Disk: 0%... 10%... 20%... 30%...100%...
Copying installer files to disk...
Copy complete.
Making disk bootable...
Copying boot files...
Copy complete.
Done.
Marks-MacBook-Pro:~ Mark$

You should now have a bootable USB drive from which you can boot your Mac and perform a fresh install of the Max OS X operating system.

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