Sometimes the worst happens. Computers are imperfect products. They fail. Macs are no exception, fanboy wishful thinking to the contrary. Sometimes everything else fails, and you have to start from scratch. That means reinstalling the entire operating system from scratch.

Officially, Apple recommends restarting your computer, holding down Cmd-R, and downloading the necessary software from the internet. However, if you don’t have internet access or don’t want to wait for the download, you can always try to install OS X from a flash drive. It’s easy- all you need is 8 GB of storage and another Mac.

Reinstall OS X From a Flash Drive

Set up the USB Drive With Mac OS Installer

In order to save your Mac, you’ll need a Mac. You can set all this stuff up before a crash as a precautionary measure (which I recommend). If you don’t, try visiting the Apple store and asking for them to help.


First, download a copy of Mountain Lion from the Mac App Store. If you’ve not already bought it, the OS is only $20. If you have, go to Purchases, hold down Option, and click “Download.” 

Insert the flash drive (at least 8 GB). Press Cmd-Space and type in “disk” to open Disk Utility. Click the drive in the left-hand column and go to “Partition.” 


Choose the “Mac OS Extended (Journaled)” format, then GUID Partition Table. Finish the installation.

Once that’s done, open a new Finder window. Navigate to the Applications folder, right-click on OS X Mountain Lion.app, and select “Show Package Contents.” Go to /Contents/Shared Support and copy “InstallESD.dmg.” Paste it anywhere you can find later. Be sure to mount the file.


Go back to Disk Utility, select the newly formatted USB stick, go to Restore, and click “Image…” Then select the mounted DMG file. Drag the USB stick from the left-hand menu to the “Destination” spot. Click “Restore.”

Once it’s done, eject the USB stick from Finder. Your USB installer stick should be ready!

Using the USB Installer

When you need to use the installer stick, plug it into the computer and reboot. When the computer turns on, hold the Option key. This will display a menu of bootable hard drives.


Using the arrow keys, navigate to the USB drive. Hit enter to select it and boot up to the installer.

After that, it becomes a matter of waiting. Just let the installer do its thing and reinstall OS X.

Alternative Courses

Like we said before, you could always try rebooting while holding Cmd-R. As long as you’ve got a good internet connection, it should restore the Mac just fine.

If you can convince your local Geniuses of your technical ineptitude, they may also take pity on you and offer to fix the computer for you. If nothing else, you could check out Apple’s new line of iPhones while you wait. Doesn’t that sound nice?

Final Thoughts

Hopefully none of this will happen to you. But, if it does, it helps to be prepared with a USB stick that can reinstall OS X from scratch. It just might save your Mac and a lot of frustration that comes along with a crashed PC.