So, our SOP for migrating users to new computers is to create a disk image of their old computer. This is the very first thing we do. There are two reasons for this. First it gives us a safety net incase we do something really stupid that wipes out their original data before we have imported it (yes, that has happened). Second, it is actually faster.  Not much, but enough to make it worthwhile. We also keep this image around for at-least one month just in case we missed something during the import process.  We keep them around longer if space is available, but we will not delete them before one month is up.

After the disk image is created and the computer base image has been installed, we normally mount the disk image and run Migration Assistant to import their user account.  Only that doesn’t work in 10.9 Mavericks any more (actually I think it is broken in 10.8.5 as well). The reason is simple, although a bit frustrating that Apple didn’t account for this.  The new Migration Assistant logs the current user out before starting. I’m sure there are very good reasons for this.  But a side effect is that Mac OS X, rightly so, unmounts all user-mounted disk images when the user is logged out. This means the disk image containing the old computer data is unmounted as well, which is why we can’t find it in Migration Assistant.

I found a solution via some command line tools.  It is easy, but unfortunately takes some documentation since it isn’t something you are likely to do that often. So, fire up the Terminal app and use this simple (but not easily remembered) command:

sudo hdiutil attach /Path/To/Image.dmg

The hdiutil command will mount the disk image.  The sudo part, if you are not familiar with it, will run the command as the root user. When a disk image is mounted as the root-user it is not automatically unmounted at logout, which makes it available to Migration Assistant. And since Migration Assistant also runs as the root user, this is fine since it can still access all the data it needs.