HOWTO: Install and Boot OS X On a Flash Drive

Remember when it was first revealed the Windows XP could be installed and booted off of a USB flash drive? Well, great for Windows users. What about Mac users? We were left out in the cold. If one were to search hard enough in the vast Web index that is Google, one could find just the snippets of how to boot a system from a USB drive, how to set a drive as bootable, yadda yadda yadda. Nothing guiding the way to creating a bootable installation of Mac OS X on a flash drive. I'm here to help.

Before I begin, let me say that I have been a Mac user for only two years. I made the switch, and I've learned enough about OS X in that time to let me do this. So, without any more small-talk, let's get into it!

Before You Begin

You will need a 1GB or larger flash drive. It is impossible to install OS X on anything smaller. After testing this procedure multiple times, the largest free space I had after booting up was 11.6MB.

You will also need the original Mac OS X Install Disc(s) that came with your computer.

Preparing the Flash Drive

Start out by completely formatting your flash drive. Open up Disk Utility, select your device from the source list (mine's a SanDisk Cruzer), and click on the Erase tab. Be sure the filesystem is Mac OS Extended (Journaled), and uncheck the option to install Mac OS 9 drivers. Space is crucial, and there will be no point in having OS 9 recognize our device if we're trying to get it to boot into OS X. Enter a name for your drive, and click on Erase.

If you click on the new drive name, you will see that Owners are not enabled.

We have to get that changed. Open up Terminal.app, and enter the following command:

sudo /usr/sbin/vsdbutil -a /Volumes/iTote

Be sure to change the name of the volume (iTote) to correspond to the name you gave your flash drive when you formatted it.

Owners should now be enabled.

Installing the Base System

In order to extract the critical system files and install them on the flash drive, we have to use Pacifist. Insert your Mac OS X Install Disc, and open Pacifist. When Pacifist recognizes the disc, click on Open Apple Install Packages.

Select your install media and click OK.

If you are prompted to insert another disc, click Skip. The files we are looking for are on the first disc.

After the package list loads, expand EssentialSystemSoftware, then EssentialSystemSoftwareGroup. The two packages that are needed in order for OS X to boot are BaseSystem and Essentials. Select them, then click on the File menu.

Select Install Files to Other Disk…

And choose your flash drive. Click Install to begin extracting and installing. This will take a while.

Remove Unnecessary Files

If you are using a drive smaller than 2GB, you will have to remove a few files before you can continue. Open up your flash drive, and navigate to /System/Library/Fonts. Scroll to the bottom, and you will find a group of Japanese and/or Chinese fonts. Removing these will free up over 100MB. DELETED! Be sure to empty your Trash.

Copy Missing Files

Because we extracted the system with Pacifist, there are a few files that are missing off our flash drive. Open up your main hard drive which has your running copy of OS X installed. Navigate to /System/Library/CoreServices. Copy SetupAssistant over to /System/Library/CoreServices on your flash drive. It might be easier to have two separate finder windows, as you will have to authenticate yourself when you copy the file.

Now we need to copy the package receipts for BaseSystem.pkg and Essentials.pkg onto our flash drive. Open your main hard drive again, and go to /Library/Receipts. Copy both BaseSystem.pkg and Essentials.pkg over to /Library/Receipts on your flash drive.

Make the Flash Drive Bootable

Now that all the required files are present, it's time to make the system recognize the device as bootable. Open up Terminal.app once more, and enter the following command:

sudo bless –verbose –folder "/Volumes/iTote/System/Library/CoreServices" –bootinfo

This command "blesses" the CoreServices folder, which makes the system recognize it as an installed operating system. Again, be sure to substitute the name of your flash drive for the volume name in the above command.

Fixing File Permissions

When the files were copied from the installer CD, they didn't have the correct permissions to allow the system to read and write to them. Open up Disk Utility, and select your flash drive. Click on Repair Disk Permissions, and go get yourself a coffee while it runs.

Booting From the Flash Drive

If you have an Intel Mac, you should be able to set the flash drive as the Startup Disk in System Preferences. For PowerPC Mac's, things are a bit more complicated. I'm not going to re-invent the wheel, so I'll forward you on to this article.

In Closing

Before you start complaining that this technique does not work with Intel Mac's, be aware that I have not tested this on an Intel Mac because, well, I don't have one. If anyone has an Intel Mac, please let me know if you can get this working, and what differences there are in the procedure.