Here's my current setup. I have both Mac OS X 10.8 and Windows 7 installed on a SSD, and Paragon drivers for each installed on each. (so I can read/write to the other partition from both partitions)

I have several games installed on Steam on Windows, and Steam is currently not installed on Mac OS X. Some of the games are compatible with both operating systems. I've transferred the files from one OS to another, and Steam accepts them and after downloading a small amount (less than 100mb) and they work just fine. So most of the game files will work fine on either OS. I'm okay with having two copies of some small things, but I don't want two of the entire game.

So I'd like to store the games on one OS, preferably Windows, and play the OS X compatible ones on OS X without just installing them again on OS X.

tl;dr, I want to play Source Engine games on both OSes of my dual-boot setup, while maintaining only one copy of the game files.

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    As someone in the same situation, I'm shocked copying the games worked at all! Have you tried non-source games? – chmullig Apr 2 '13 at 1:26
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    It probably deleted the files for the other OS when you copied them over and validated them with Steam. You might not be able to prevent that if you're trying to use the same files dual-booting. – SevenSidedDie Apr 2 '13 at 3:10
  • I just installed Steam for Mac and pointed it at the Windows steam folder, and it detected CS:GO. After a 40mb download, it works fine. CS:GO is still working on Windows. However, other games were not detected automatically on OS X. – danielcg Apr 2 '13 at 20:26
  • @chmulig It probably won't work with non-Source engine games, unless they work the same way (using the same content files across operating systems) – danielcg Apr 2 '13 at 20:35

A lot of the files, such as assets (images, textures, models), config files etc, are shared between Windows & Mac - They are the same files and can be used on both Windows and Mac without problems as proved here:

Do Mac and Windows versions of Source games contain the exact same files?.

However, the actual executables (.exe for Windows, .app for Mac) and library files .dll for Windows, .a for Mac) differ greatly (and are written differently, so you can't just change the extension and hope for the best).

Assuming Steam doesn't remove the Windows executables when you verify game cache on the Mac side (as SevenSidedDie fears), then theoretically you could get away with installing Steam (just Steam!) on the Mac side of things, and creating symbolic links to the files and folders that you need.

You will need to create symbolic links to

  • The Game's directory in the steamapps folder
  • Any Source .GCF files in the main directory (I can't remember what they're called off the top of my head, I will have a look when I get home, otherwise feel free to edit them in!)

Here is an answer I posted about creating symbolic links in Windows: Team Fortress 2 won't install on custom location.

Just remember to create Directory links for entire directories, and File links for individual files.

Thanks to SevenSidedDie, I now know how to create symbolic links on a Mac! :) The command is:

ln -si <real file/folder path> <link name>

As pointed out, some programs wont follow symbolic links, but I've never had a problem doing this for Steam on Windows.

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    On Mac there is the usual unix command: ln -si <real file/folder path> <link name>. They'd have to be symbolic links (the -s part) rather than hard links, since it's across different logical drives, and some programs will not follow symlinks, seeing them instead as normal (and empty) files. – SevenSidedDie Apr 2 '13 at 6:07
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    Steam would have to be installed on both operating systems since the Steam executable isn't a universal executable. Its also likely the asset files are not exactly the same depending if the same engine is used. It really depends on the specific game in question. – Ramhound Apr 2 '13 at 17:57
  • I'm okay with two copies of the Steam client, or even small OS specific files for games. But two copies everything won't work, I don't have enough disk space. Even if I did it would bother me that I was wasting my space. – danielcg Apr 2 '13 at 20:28
  • I tried simply installing Steam for Mac and pointing it at the Steam library folder on my Windows partition; and it worked a little. CounterStrike Global Offensive was detected automatically, and after a ~40MB download works fine. Other games, however, were not. If I install and then verify integrity via Steam, it sits at 100% forever and simply downloads the game in the background. I'm going to try the linked files method, probably in a few hours. – danielcg Apr 2 '13 at 20:44

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