Fix Gnome Software Stuck With "Software catalog is being loaded" Message

"Software" is the default Gnome graphical tool for installing applications and extensions. It's used not only in Linux distributions using the Gnome desktop, but some others as well, like Xubuntu (Xfce-based Ubuntu) for example.

Sometimes Gnome Software doesn't load, getting stuck in the "Software catalog is being loaded" phase. I had this happen on both my laptop and my desktop (one running Ubuntu and the other Fedora) a few times, and the only fix that worked in both cases was to remove the Gnome Software application cache, and kill Gnome Software (because the application continues to run in the background even after it's closed).