Remember when Migration Assistant worked with Disk Images?

Apple Disk Image IconI don’t exactly recall when Apple’s Migration Assistant started logging out the user (10.9ish), but since then it has been a little more irritating to migrate from a dmg or other image format (as opposed to a source hard drive or time machine backup).  Here is a simple Terminal command to mount the image as root and thus keep it mounted after logout.

sudo hdiutil attach diskimage.dmg

This process does require running a checksum, and for larger images that could take a while.  Once you run this command and it completes its verification of the disk image, simply run Migration Assistant and complete the migration.  After migration and a restart, the image is unmounted and you are ready to work on your newly migrated mac. (note: migration can also take quite a while depending on the amount of data)