Eventually, every Linux user opens an app and finds a generic placeholder icon staring back from their dock/panel. It looks like the dock is broken, but it almost never is - the cause is a single line in the app’s .desktop file, and it only takes a minute to fix. Here’s how to find it and fix it yourself, on any desktop.

As the maintainer of Plank Reloaded, the most common bug report I get is “this app has the wrong icon.” It’s almost never the dock - it’s a broken StartupWMClass in the app’s .desktop file. So I wrote up how to find the right value on X11, Wayland, and KDE, and why deleting the line often fixes it.