How To Create An OS X Mountain Lion Install USB Drive

With OS X 10.7, a.k.a. Lion, Apple stopped shipping physical copies of its operating system and instead opted for electronic delivery via its then-brand-new App Store. For the first time you could update your current configuration to the latest Apple OS with just a couple of clicks, a few restarts, and about 90 minutes of waiting.

Performing a clean installation, on the other hand, was a bit problematic. Lion also introduced a new recovery partition, and if you wanted to perform a clean installation, you had to run through a lengthy process of first installing it over Snow Leopard, rebooting into the recovery partition after the upgrade had completed, and then whipping over to your boot drive and installing the new OS on top of the now-clean boot drive. This was a pain in the tush because you had to install the OS twice: once to create the recovery partition and again to put the clean OS on the drive.

BYTE figured out a way to bypass this extra installation and wrote it up in How To Create an OS X Lion Install Disc. However, even this workaround was a bit involved for most people.

In this updated how-to, we've got a simple way for you to create not only a boot disc for Mountain Lion but Lion as well. The key is a handy app called Lion Disk Maker. The app uses Apple Script with a very nice GUI in front of everything.

To begin, download Lion Disk Maker. It comes in the form of a zip file. Unzip it and move it to your Applications\Utilities folder.

Navigate to your applications folder and double click on the Lion Disk Maker icon. The app works for both Lion and Mountain Lion. You get to choose the version you want to make a boot disk for once the app starts.

For this how-to, I chose Mountain Lion. You will need to have a copy of the Mountain Lion installation app, purchased from the App Store. After you click the "Mountain Lion (10.8)" button, the app will search your home directory for the install app. You can use the copy it finds or you can choose a different copy. I chose the copy that it found and clicked the "Use this copy" button.

Lion DiskMaker will open the app contents and find the InstallESD.dmg disk image. You have a choice of creating a bootable DVD or bootable USB stick. I decided to create a bootable USB stick, and clicked the "Create a boot disk" button.

It's strongly recommended that you use an 8GB thumb drive. The contents of the disk image you're going to be burning are just over 4GB, so the 4GB version that might have worked for Lion won't work for Mountain Lion. Click the "An 8 GB USB thumb drive" button.

The app assumes that you have already inserted your thumb drive into your Mac and have appropriately initialized, formatted, partitioned, and named the drive. Choose the drive from the drop-down list and click the "Choose this disk" button.

The utility will erase everything on the thumb drive. If you need to get anything off it, do so before you click the "Erase then create the disk" button!

The app now will copy files to a temporary disk image. The horizontal barber pole does nothing but spin, but you can watch the file names underneath it fly by.

During disk creation you'll see the system mount a number of different disk images. If you look for them in Finder, you'll be able to see that it's grabbing important system apps and applets and holding them in a temporary location so the contents can be copied to your thumb drive.

After it has the files it needs, the app will burn the contents to your thumb drive. After a few minutes it should finish.

If you get this error message, don't worry. Just click the OK button and you're done. Restart your Mac while holding down the Option key to go to the boot loader. Choose the EFI Boot, USB disk option. This is your Mountain Lion boot disk and it will provide you with the same tools and utilities you find when you boot to a Mountain Lion recovery partition.

Clicking the Edit button launches an Apple Script editor. If you're fluent in Apple Script, you might be able to make the error message go away or you might not. Regardless, the thumb drive you just burned, booted to, and tested works just fine, so don't sweat the small stuff.

If you get this error message, don't worry. Just click the OK button and you're done. Restart your Mac while holding down the Option key to go to the boot loader. Choose the EFI Boot, USB disk option. This is your Mountain Lion boot disk and it will provide you with the same tools and utilities you find when you boot to a Mountain Lion recovery partition.

Clicking the Edit button launches an Apple Script editor. If you're fluent in Apple Script, you might be able to make the error message go away or you might not. Regardless, the thumb drive you just burned, booted to, and tested works just fine, so don't sweat the small stuff.