On Linux the
/ is the root directory, so yes it is the “top-level” directory. Your
/home directory for your user is under this root directory. If I remember correctly, this means your user’s directory under the
/home directory is on its own partition. So taking my first name as an example
/home/brad is allocated 80gb of memory to do what I want in that directory since its mine.
It sounds like you setup 20GB to your overall distro installation, and 80gb for anything under your user’s
/home directory. The issue with this is generally anytime you install anything on your system, its not installed under your home directory. Rather its installed under one of the “top-level” folders and “provided” to users of the system.
I’d recommend looking into moving around some memory so your root partition has more room. There are a few articles on doing this but I recommend you look into multiple. If anything, backup your important work before you start playing around.
Worst case scenario, you can backup your data, nuke your partitions and start again with a different setup.