One Computer, Multiple Users, Multiple iTunes Libraries

Question

Hello
My family shares a single Mac via Fast User Switching. We all have separate iTunes libraries. I had some difficulty getting TV to be able to use all of the iTunes libraries as alternate sources for streaming music. I'm posting this here as I've noticed a couple of questions here about it with no solutions.
The symptom is that you are able to add the multiple libraries to TV by entering the passcode in iTunes but when you try to the new source, it fails to load the library. 'Loading <library> name ...' goes on forever or eventually gives up and then the library appears grey in the source list and you have to go through the registration process again. Music sharing appears to work between copies of iTunes running on the same computer.
It's a firewall problem.
It seems that iTunes choose a new TCP port to share each different library. For me it seems to allocate ports in the 4915x range. I can't find any documentation about this. The ports are not listed in the well known list for Apple products. I discovered it because the Windows version of iTunes has an informative error message that tells you to check that a particular port is open in the firewall for the particular library when it fails to load it.
To fix it you just need to open these ports in the Mac's firewall. After that, provided all the users remain logged in with iTunes running, you will be able to stream their libraries.
I hope this helps others to get it working more quickly than I did.
I see that there are some Apple employees participating in these discussions. If you see this, maybe you could modify the documentation? Or add the solution to the How-To pages? I'll submit some feedback anyway.

Answer 1

I wrote a simple shell script that executes each time a user logs in (well, actually, each time I log in, coz' it's not really applicable to other users). It syncs my work and home addressbooks and iCal calendars to one another.
I named it "sync". Then I read somewhere that if you wanted to make it double-clickable (to launch it from the Finder), I appended a ".command" filename extension (so it's now named "sync.command"). I also did a chmod 755 to that file so that it had execute privileges. Depending on whether you give each user their own copy of this thing, or keep a single copy in, say, the /Users/Shared directory, you may have to play around with chmod. Whatever, just so long as the user that has just logged in has execute permissions to the file, and to the entire path to the file, you should be good.
Then, in SysPrefs > Accounts > Login Items, I added that "sync.command" file to the list. So, really the only difference is I'm not wrapping mine inside an Automator script like you are.
I had tried adding it to ~/Library/LaunchAgents and make a launchd plist for it, that would kick it off at login. But I didn't get that to work. Don't know why. But just adding the double-clickable executable unix script to the Login Items list did the trick. Whether the plist has to hang out there with it, I don't know. I still have it there, though, in case I ever get motivated to figure out what's wrong with my launchd plist file. So, if just adding it to the Login Items list doesn't do it for you, you could try making a (functional?) launchd plist for it and plopping them both in ~/Library/LaunchAgents, too. That's how I am now, and, like I said, it launches at user login as that user's process (not as a root process like the above referenced article said how login hooks worked -- although, you may want it to run as root since you want this to work with multiple users...in which case, you might want to listen to Cole and not me...).