Install mac os x on an external hard drive: this is how it works

As a system for on the road or for testing developer versions – installing Mac OS X on an external hard drive can be very handy. We show step by step how to install the system.


First of all the hint: An external drive, no matter if USB stick, hard disk or SD card, with Mac OS X can only be booted with a Mac. This is not a Hackintosh tutorial, conventional Windows PCs can’t do anything with disks created this way. Now let’s get started: Install OS X on an external hard disk: Here’s how!

1. Have an external data medium ready

alt="disk-usb-sticks" height="" /> We need about 8 GB of free space for an OS X installation on the external data carrier. An appropriately large USB stick or SD card is therefore a prerequisite. But of course a small external hard drive works just as well. Especially if you want to store some files on the external system, a little more space is an advantage. For our example we use an SD card with 32 GB.

2. Format& Partitioning

Our hard disk must now be configured as target medium. For this we start the Disk Utility (best done via Spotlight).

Here we select the target disk on the left and click on the tab Partition. The Partition Layout list allows the selection 1 partition. Under Options, we now specify that we want to use the GUID partition table want to use. As a name we can enter anything, the format should be Mac OS Extended (Journaled) its. A click on Apply apply the settings to the disk.


Now we are ready to install OS X on the external hard drive.

3. Locate the installation file of OS X

The first look goes into the folder Programs. There some of you will OS X Mountain Lion installation (or similar, depending on the version of OS X) will find. If we start this program and accept the software license agreement, we will be asked to select the target medium. Here is now the hour of our external data medium come. Select, confirm and off we go.

Do not panic- if you search for the installation file in vain, just continue reading! Everyone else is ready here and just has to follow the instructions during the installation process.

3.1. Locate the installation file of OS X (only for Macs that don’t have an installation file in the Applications folder)

On Macs already equipped with the latest version of Mac OS X 10.8 were delivered, we look in vain for an installation file. One solution is to download the operating system again from the App Store. But if you never did that, but got the Mac with the system pre-installed, you would have to pay for it.

However, with a few terminal commands, we can download the needed image using the recovery partition.

  • To do this, first enter this command in the terminal application:
  • diskutil list
  • diskutil mount readOnly /dev/KENNUNG
  • hdiutil attach "/Volumes/Recovery HD/"


After a few moments, the basic system should have booted up. Here you can find beside some system folders the file OS X Mountain Lion installation. From here, everything almost goes by itself – just follow the instructions on the screen.

However, the actual installation files are first downloaded from Apple. This takes some time, because depending on the internet connection the 4 GB are not done in a few minutes.

4. Boot Mac OS X from the external drive

To restart the system from an external data medium, we hold down the alt keypressed. You will now see the available disks that the Mac can boot from. Alternatively, we can also reboot directly from a running system from a specific target disk.

In the system settings we find the entry Startup volume, under which we can select the desired destination and restart directly.

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