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I want to configure the same user account across multiple operating systems. Right now, I'm set up for general use in Mac OS 10.6.6 "Snow Leopard," and I have about 200gb of files in my home directory (/Users/justjake/). I want to use this user (and home directory) for other operating systems on other partitions. For example, I have Mac OS 10.5 installed on a 12gb partition. How can I share permissions, user accounts across my two operating systems?

Would moving the my /Users directory from 10.6 to it's own partition then mounting it using /etc/fstab solve my issue?

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Are you sure that Mac OS X 10.5 and 10.6 will be happy sharing ~/Library ? Some files/formats cannot be used by older the older OS. – Madison S Mar 5 '11 at 22:43
That could be resolved by using an script during upstart creating a symlink. Like ln -s XXX/Library-10.5 XXX/Library and ln -s XXX/Library-10.6 XXX/Library together with:… – Darokthar Mar 5 '11 at 22:52
@Madison S They'll probably fight a bit if I left system preference files in place, but I could just swap links or something with a startup script between hidden subdirectories, like linking ~/Library/Preferences/ to ~/.private/Library105/ or ~/.private/Library106/ based on an if statement in a shell script on boot. Or I could do something else. This seems like a lesser problem. – Just Jake Mar 5 '11 at 22:56
The main thing (that I can think of) is that both accounts have the same userid. It's detailed either here, or – tobylane Mar 18 '11 at 22:09
up vote 2 down vote accepted

Files in Mac OS X generally have have an owner user id and group id, and permissions for their owner, members of the group, and all others (Wikipedia).

You should make sure that your user accounts on both systems use the same user id. The default group on both systems is probably staff for most files (which is OS X internal), so that shouldn't be a problem.

You can configure the location of your home directory as well as your user account ID from the Accounts preference pane in OS X. Just right-click on a user, and select Advanced Options…:

enter image description here

Ensure both user accounts have the same numeric user ID (but don't change the current home directory owner's user ID, unless you want to change all these permissions), and point both user accounts to the same home directory, e.g. on a third partition used by both systems, or even on one of the system partitions, like /Volumes/SLPartition/Users/username. Alternatively, as you said, mount a partition at /Users/danielbeck using fstab -- FileVault uses a similar mechanism (mounting a disk at /Users/username), so you should be fine doing that.

Just make sure both systems have another unrelated account with administrative privileges in case something goes wrong with your configuration. This way, you can more easily change settings around.

Remember that OS X and integrated applications (Safari, Mail, iCal, Address Book, etc.) might not be too happy sharing parts of ~/Library. The same goes with some applications, even third party: Be sure to use compatible application versions wherever possible. Be sure to create a complete backup before doing this -- There might be rather unexpected problems. You could solve them by e.g. symlinking problematic files and folders back to each systems main disk, e.g. /Users/Local-Username, and keep system-specific data locally.

Depending on what exactly you want to do, it might be a better idea to just symlink ~/Documents, ~/Music, etc. to another partition.

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Sorry I didn't approve this in time; I was backpacking and I dent realize it'd autoconfirm. Thanks for the great answer. – Just Jake Mar 26 '11 at 1:23

just. don't. do. it. :-)

sharing $HOME directly between systems like OS X that are so dependent on what's in there will make you unhappy. Trust me, I tried.

What I recommend instead is to create a folder structure inside $HOME that can be symlinked from elsewhere, that keeps your "work" files. For instance, I have a directory "current" where my current projects live. And a directory "done" (upvotes to whomever guesses what that does). On one machine, they are plain directories in the Documents folder. On other machines, original:/Users/fl/Documents is mounted and then the folders symlinked. Looks the same to the user :-) and you can even use it for all OS flavors you work on.

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