[donncha]

Hi,
I need to set up a machine for both development and testing, with a separate OSX install for each. I plan on having 3 partitions: 2 partitions with OSX installed on each, and a single Users partition.

Will this work? WIll there be an issue if there's a particular user account under one OS but not the other? Any other issues anyone can think of to watch out for?

thanks for your help,
donncha

[Brass]

I was planning to share a /Users folder between 2 installs (not on its own partition, but on the same partition as one of the OS X installs).

However, I decided against it because I'm using 2 different versions of Mac OS X, and many of the Mac OS X components and bundled applications will be using different preference file formats. While the newer version will probably read the older version's file format the older version will not read the newer, and may behave strangely, or overwrite the preferences altogether.

A semi-work around could be to keep your main "Documents" diretory outside of your home directory, and share the Documents directory between both. You could then have a link/alias to this Documents folder in both of your home directories, instead of an actual Documents folder.

It's unlikely that you'll be using different document formats for different OS X versions, but it is possible if you're using different versions of an application on different installs, so it's something to be wary of.

[wataru]

That sounds dangerous. You shouldn't share ~/Libraries across different versions of OS X. If you're not sharing ~/Library, then you're not really sharing accounts. You could, however, keep all of your documents on a separate partition and share them between systems, but that's not the same thing as "sharing an account."

[Detrius]

If it's two completely different versions of OS X, it's not recommended. If you are running two similar versions, though, you can change the home directory location in Netinfo. You will also have to make sure that the users on each OS install have the same UID; otherwise, users may not be able to access their own home directory.

[JNI]

When I first installed Panther on a separate partition from my Jaguar installation I wanted to share my home folder for both. I was a bit concerned about the ~/Library folder compatibility, so I linked all the separate folders except the Library folder of my Jaguar home directory to my Panther home. That worked for the most part, except that the links didn't always work in all situations (like when doing AFP mounts on another machine, ftp listings etc.) It was also a problem whenever I added another folder or file to my home dir - I had to constantly keep the links up to date. The biggest pain was linking all my dot files sprinkled in my home dir, like .ssh, .cshrc, .profile, .emacs etc.

This issue came up on the Apple dev lists, since it is common for developers to have multiple bootable partitions and are frequently erasing entire partitions for fresh installations of alpha/beta releases. Some Apple engineers posted that what they do is to change their home folder using NetInfo to point to a common home folder. They mentioned the possible Library issues, and said that it 'shouldn't' be a problem, since any incompatible prefs etc should just be ignored (or handled gracefully) by the current boot system or any applications. They said that they explicitly attempt to keep compatibility in mind in prefs files and such for Apple apps, since they realize the need/desire to share a home directory that may be booted from different versions of the OS. That model should be understood by third party developers too. The idea of having a single home directory on say an NFS mounted server is a long standing technique for Unix systems, so it is not a new or hacky idea.

When installing Tiger I decided to take a leap of faith and now share a single home dir for Tiger and Panther and I haven't had any problems <yet>. Of course I backed up the Library folder just in case, but so far so good.

So, although there is a potential issue in sharing a Library folder across different versions of the OS it seems to work for many people, and it has been 'unofficially' recommended by Apple engineers. If there is a compatibility problem, it should be considered a bug. Application developers should do 'the right thing' and allow this technique to work without significant problems. E.g. any new prefs that are only valid for a specific OS version should have different tag names, or should be translated as nessessary. Any plug-in or whatever that requires services only in a particular OS version should be testing for that kind of thing anyway and handle it gracefully. I pretty much trust the Apple apps in doing the right thing, but of course third party apps and extensions may be more susceptible to problems.

So far for me, I'm loving the fact that I no longer have to try to keep two home dirs in sync with all kinds of manual link creation etc. YMMV.

[Millennium]

This is theoretically possible, but it is dangerous. Keep Detrius' advice in mind.

[CatOne]

Originally posted by wataru:
That sounds dangerous. You shouldn't share ~/Libraries across different versions of OS X. If you're not sharing ~/Library, then you're not really sharing accounts. You could, however, keep all of your documents on a separate partition and share them between systems, but that's not the same thing as "sharing an account."

Well, I had 10.2 and 10.3 (betas, for about 4 months) share a home folder (including ~/Libraries) with no issues. I just used a symbolic link from the 2nd partition back to my home folder -- worked fine.

Maybe not 100% advisable, but hey keep a backup

[JNI]

Originally posted by Millennium:
This is theoretically possible, but it is dangerous. Keep Detrius' advice in mind.

Not to get into a semantic or religious argument, but it is more than 'theoretically possible', it is absolutely possible, and done by likely thousands of people every day. The Apple engineers say they do it that way, and I'm pretty sure that school/lab environments where user's home directories are on servers is done that way too. Granted, they may have more control over which versions of the OS the user is accessing from, but that is not a guarantee when going from one lab to another even within the same institution. Again, it is a feature of Unix/OSX to support automounted and dynamic links to a user's home directory.

It is really no different than what happens when an existing user upgrades from Jaguar to Panther. The ~/Library folder does not get replaced. Going back in versions would be the only 'unusual' thing here. Apps should be able to handle it. If there is a problem, you may need to throw a prefs file or something, but that's no real biggie. Any incompatibilities should be considered a bug. Yes, bugs happen, but that's nothing really unique to this situation.

I'd be more apt to say it is 'theoretically possible' that you will have a problem if you share a ~/Library folder amongst different OS versions. But I have never seen any posts of anyone that has actually had problems doing it. As always, backups are a smart thing and YMMV. If you want to be very conservative, then don't do it. Then maybe you don't ever want to upgrade from Jaguar to Panther or Tiger either. But I find it has been a godsend to not have to manually keep two home directories in sync.

One more irritating thing that plagued me during the Jaguar/Panther transition was that double-clicking files would often launch the 'newest' version of an app, and if I was booted into Jaguar and a Panther-only app launched, that was a pain. I had to muck with some LaunchServices prefs and such to get that to go away, but eventually it got resolved.