Boot Mac OS X from External Drive

Wed, Oct 15

Although a tad bit off topic, it’s Mac related none-the-less. I am in the midst of backing up my MacBook Pro to a remote drive as I’ll be buying one of the new machines recently announced by Apple.

As part of the process, I am creating an image of my current system on a USB drive, using the Disk Utility application. The idea is to create a bootable image on the USB drive, verify that I can boot from the drive and use that image for the new machine. If all goes well, the process of configuring my new system such be nothing more than restoring the image on USB to the new system, in theory.

To verify all is well, that is, the USB is bootable, one can request Mac OS X to bypass the primary drive with the following key sequence, during bootup:

Press and Hold: Option-Command-Shift-Delete

I found this tip, along with many others keyboard shortcuts on the Apple support website.


If this is the case, then why is everyone complaining about the loss of firewire? How does this differ from target disk mode?

by David on Oct 15, 2008. #

The way it differs, is that you have to restore the image each time, rather than editing your install directly.

by Thanh on Oct 21, 2008. #

You can also hold down the option key while booting to get a menu of bootable devices.

by Andy Kim on Oct 24, 2008. #

Another solution if you plan to boot from the external drive frequently (and are using an Intel-based Mac) is to install rEFIt. rEFIt is a boot loader that allows you to select which O/S instance to boot from when your machine first starts (much like the bootable device list you get from holding down the option key, but with a lot more options…

You can get rEFIt from:


by Steve Dussinger on Mar 10, 2009. #