System Information

• Steam client version: Jun 8 2017, at 04:34:18; Steam API: v017; Steam package versions: local
• Distribution: Ubuntu Mate 17.04 x64
• Opted into Steam client beta?: Yes
• Have you checked for system updates?: Yes

The issue in as much detail as possible:

Steam client has an option to show CD Key of certain games. Here are those games:

ShowCDKeyOnLaunch: https://steamdb.info/search/?a=app_keynames&keyname=179
ShowCDKeyInMenu: https://steamdb.info/search/?a=app_keynames&keyname=181

However, as I found out, Steam for Linux is unable to show cd keys of non-Linux titles:

Here is the CD Key output of Warhammer 40,000: Dawn of War - Game of the Year Edition:

• Steam for Linux: https://yadi.sk/i/XgOE57633K3cgM
• Steam for Windows via PlayOnLinux: https://yadi.sk/i/1XjAUZ4l3K3cgY

When I try to see the cd key of a Linux game, Steam for Linux instantly shows the key:

Cities in Motion 2 via Steam for Linux:

https://yadi.sk/i/MZ9wymlo3K3d8T

As it turned out Steam client two different method to show CD keys; ShowCDKeyOnLaunch and ShowCDKeyInMenu. Apparently, CD key "option" of the games that use ShowCDKeyOnLaunch method does not show up on Steam client if the games don't support that OS (eg Linux). FlatOut: Ultimate Carnage which uses ShowCDKeyOnLaunch method is an example of that:

Steam for Linux: https://yadi.sk/i/6lVS9Hjx3K5AiM
Steam for Windows via PlayOnLinux: https://yadi.sk/i/2NZHmMaP3K5Ai5

On the other hand, CD key option of the games that use ShowCDKeyInMenu method does appear on Steam client of all 3 operating systems, but CD key cannot be retrieved if the game does not support the operating system in question (eg Linux). Previously showed Warhammer 40,000: Dawn of War - Game of the Year Edition is an example of that.

A Feral Interactive employee, edddeduck_feral explained the cause of the problem on Reddit:

https://www.reddit.com/r/linux_gaming/comments/6grmop/steam_for_linux_doesnt_show_cd_key_for_windows/distlgd/

. My system information via Steam client: Github Gist

Steps for reproducing this issue:

1. Launch Steam for Linux
2. Find a game which has CD key option.
3. See if CD key option appears.
4. If CD key option is present, click it to get license code of non-Linux games.