Can I run Steam as its own standalone session?

Solution 1:

Perhaps this story might be sufficient which uses steam-login which uses xfwm4 under the covers to provide a lightweight desktop with Steam on top.

Here's the information from the README:

sudo add-apt-repository ppa:thor27-gmail/steam-desktop 
sudo apt-get update 
sudo apt-get install steam-login

Then logout and back in to get a Steam session. See also:

• What are PPAs and how do I use them?
• Are PPA's safe to add to my system and what are some "red flags" to watch out for?

Solution 2:

• Just copy the steam.desktop file from /usr/share/applications/steam.desktop to /usr/share/xsessions.

• Then edit it and change the Exec option to

  Exec=steam steam://open/bigpicture
  

  or just create you own:

  [Desktop Entry]
  X-SuSE-translate=true
  Encoding=UTF-8
  Type=XSession
  Exec=steam steam://open/bigpicture
  TryExec=steam steam://open/bigpicture
  Name=Steam
  Comment=Steam