This was a little project I embarked in at work a while back that I found to be quite a pain due to the last guide on this topic being so outdated. So here’s my update on how to create a multi-boot USB installer for Mac OS X…
It is very important to follow this documentation precisely. If you do not follow it precisely, one of the installers may not work.
It is also important to note that this documentation is composed in a manner suitable for intermediate-advanced Mac OS X users/technicians/administrators.
Make sure that you have “show hidden files and folders” enabled before following the steps below.
1. Format a 32GB+ USB in to four GUID MacOS extended (journaled) partitions using the Disk Utility. Make the first partition 200mb (.2gb) and the rest 10gb each.
2. Mount the Mountain Lion dmg. Restore the “BaseSystem” in the Disk Utility to the second partition. Unmount the dmg.
3. Mount the Mavericks dmg. Open it and mount the “BaseSystem” dmg. Restore “OSX Install ESD” in the Disk Utility to the third partition. Open the third partition and navigate to “System>Installation” and delete the “Packages” shortcut. Open the “OS X Base System” dmg and copy the “Packages” folder to the “System>Installation” folder on the third partition.
4. Mount the Yosemite dmg. Open it and mount the “BaseSystem” dmg. Restore “BaseSystem” (NOT “OSX Install ESD”) in the Disk Utility to the fourth partition. Open the fourth partition, navigate to “System>Installation” and delete the “Packages” shortcut. Open the original “Restore OS X Base System” dmg and move the “Packages” folder to where the shortcut was deleted on the partition. Open “OSX Install ESD” and move the “BaseSystem” dmg and chunklist files to the main directory on the partition. Unmount the dmgs.
5. Open the Mountain Lion dmg. Right click on the .app installation file and click on “get info”. Then right click on the mounted Mountain Lion partition on your desktop and open “get info” for it. Click on the icon in the top left corner of the installation file’s “get info” window and copy it, then paste it in the same spot for the partition’s “get info” window, replacing the old icon.
6. Open the Mavericks dmg, then the BaseSystem dmg, and do the same thing with its .app installation file and corresponding partition.
7. Do the same with the Yosemite dmg and its corresponding partition.
8. Download rEFIt. Restore it to the first partition.