February 25, 2011

Dual booting your Mac while sharing your Home directory

If you wanted to dual boot your Mac — let’s say between “Snow Leopard” and “another version of OS X” — one way to do it would be to partition the drive and share the Home directory between both installations.

The Disk Utility program in OS X can partition a drive without losing data on the drive. That said, don’t proceed without a bootable, verified backup.

How to

I’m going to show you how to change this on Snow Leopard, rather than show you screen shots from “another version of OS X” which may or may not be pre-released.

Be sure to read through this entire post before you actually make any changes.

The process is the same, even if the name of the Preference panel may or may not have changed to something slightly different than “Accounts” which is what it is called under Snow Leopard.

launch that preference panel, be sure it is unlocked (see lower left corner), and then option-click (aka “right click”) your account to reveal “Advanced Options”

The “Advanced Options” will open, revealing several possible things you can change, including your Home directory:

Click the “Choose” button and navigate to the new folder.

Stay away from the User ID, UUID, and Aliases fields unless you know exactly what you are doing.

Warnings, Disclaimers, etc

I can say from personal experience that this appears to work and appears not to cause any problems for me, but I have only done limited testing and I had a complete bootable backup in case anything went wrong. If something goes wrong, I accept that I may have to reinstall my applications and copy over my files manually once the version of OS X after Snow Leopard is released. In fact, I will most likely do an entirely clean installation of OS X when the new version comes out. So I don’t worry about “long term ramifications” because the whole thing is going to be wiped in a few months anyway.

I did not make this change in my Snow Leopard partition. I made this change on the other version of OS X and pointed it at /Volumes/Snow Leopard/Users/luomat

One of the benefits of this change is that I can access files in my Dropbox (the current Dropbox.app 1.0.20 does not work with the current version of another version of OS X) while booted into another version of OS X. When I reboot back into Snow Leopard, my changes are sync’d via Dropbox.

Also

When booted into another version of OS X, I removed my ~/Applications/ folder and linked the Snow Leopard /Applications/ folder like so:

ln -s "/Volumes/Snow Leopard/Applications" ~/Applications

which gives me easy access to them. However, if I was going to install, uninstall, or update any applications, I would make sure that I was booted into Snow Leopard, and would not update them while using another other version of OS X.