Making a bootable USB drive of OS X Mountain Lion
Step 1 — Buy Mountain Lion on the App Store and wait for it to download.
Step 2 — Find an 8 GB USB thumb drive (preferably already erased and formatted to ‘Mac OSX Extended’).
Step 3 — Ignore the install screen when it appears. Open finder, go to your
Applications folder, find “
Install OS X Mountain Lion”.
Step 4 — Right click (Or Ctrl+Click) the installer, and click “
Show Package Contents”.
Step 5 — Navigate to
Shared Support. Copy the
InstallESD.dmg file to somewhere safe (like say your desktop).
Step 6 — Launch Disk Utility. Goto the Restore tab. Source = InstallESD.dmg. Target = Your USB stick. Click Restore, and wait about 20 minutes (depending on your USB drives speed). Note: I received an error: “Could Not Restore — Invalid Argument” upon completion of the USB restore. This does not appear to be a problem as the USB based upgrade still worked fine.
Step 7 — Enjoy!
That’s it. The process is really quite easy and saves you from having to re-download Mountain Lion on each machine. I’d also suggest you keep around the “InstallESD.dmg” file in case you ever need to make another USB drive, as you won’t be able to download Mountain Lion again on any machine you’ve already upgraded. Happy Upgrades!