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In the config file at


you will find lines that define

  • which tray application will be started at boot
  • which applications will float or will be tiled
  • which application you want to start automatically

You can always read more on the i3 documentation site.

Example of a floating application (<=> tiling)

Gnome-disks is a floating application. xprop is the application to figure out the naming of the window.


Contents of movie

  • find the lines in the config file
  • overview of the possibilities
  • why numlockx
  • difference of floating windows and tiled windows explained
  • MOD key and move a floating window out of the way with your mouse
  • vlc has a preference popup – checking the name
  • what tray application will be started
  • what application will be started at boot
  • I made personal shortcut keys to start the most important applications


WM_CLASS(STRING) = "gnome-system-monitor", "Gnome-system-monitor"

First part after wm_class(string) is the instance and second part is the class.

So depending on what you want to achieve you can use or class or instance.

for_window [instance="variety"] floating enable
for_window [class="Gnome-system-monitor"] floating enable