Mac Geekery

Mac OS X’s built in Migration Assistant is a little understood, little used beast. The gist is that it imports a NetInfo Database, assorted plist files, User Directories, and other data from one Mac to another, ostensibly due to the user upgrading to a new computer. Always looking to make things a little easier, I put the Migration Assistant to work as the “restore” half of my backup plan. This works great for mass Mac configuration, too. Set one up, clone it to disk with this procedure, then you can use the disk (or several disks) to quickly close user accounts, home directories, and such to a great many Macs.

Run Down

• Create a DMG file
• Load it so that the Migration Assistant thinks it has a full, running copy of OS X installed
• Load it with unique data we want migrated or restored.

Create a DMG File

This is the easiest part of the whole endeavor. Use Disk Utility, hdiutil, or other arcane methods to create a disk image the size of the media you will be using. I create 4.7GB sparse disk images that will be burned to DVD. Obviously, if you’re going to CD, you want a smaller image. I call my volume “Migration Data” and I save it into /Users/Shared so that I don’t create any recursion problems later on.

Set Up the DMG

The Migration Assistant, it turns out, doesn’t really look too deeply into a volume. If there’s a folder at /System/Library/CoreServices and there’s a nidb in /var/db, all is generally good. I load up a few extras, as well, to make it a full system migration.

$ cd /Volumes/Migration\ Data
$ mkdir -p System/Library/CoreServices
$ sudo ditto /private private
password:
$ sudo ditto /Library/Preferences Library/Preferences 
$ ln -s private/etc etc
$ ln -s private/tmp tmp
$ ln -s private/var var

That, it turns out, is all you really need. But while this will import a user entry into the new computer’s nidb and some system level plists, this isn’t the main attration, no sir.

Back Up Your Data

I create Users/jc on the disk image and load it with a DVD’s worth of my most critical data, in the same form it exists in my home dir. This works out to be my Desktop, Documents, Library, and a few other odd folders; everything except Music and Pictures, really. Those I back up separately. I also make a folder at the root of the image called Applications and load it up with any non-standard apps that can live through a drag-install. When you’re done loading it full of your data, burn the image to disk.

Disaster Strikes

This is the fun part. If you, for whatever reason, find yourself on the short end of a catastrophe and have to erase and install or even replace your hard drive, OS X presents you with the new-fangled Migration assistant. Just insert your disk, tell it that you’re migrating from another volume on this Mac, and it does the rest.