/usr directory
/usr directory in Linux doesn't stand for user but for Unix System Resources.
symlinks to other folders
/bin, /lib and /sbin are just symlinks to /usr.
/usr is the one directory that holds all the libraries and binaries that come with the OS.
Where it's used
The directory is used by all userspace applications and programs.
- systemd uses everything from here during boot.
- All installs from package managers like apt, yum, and dnf go here too.
Merged directories
Earlier, /bin, /lib and /sbin were separate directories, but they have been merged into /usr.
Currently they're just symlinks to /usr.