What is stored in the /usr directory?
/usr is the big read-only hierarchy where the bulk of installed software lives — programs, libraries, and shared data — as opposed to the small set of essentials on the root partition.
Think of it as the "everything that isn't needed for early boot" half of the system. The handful of commands required to bring the machine up live in /bin and /sbin; the vast majority of programs installed by the package manager land under /usr. Because it changes only when you install/update software, it can sit on read-only or shared storage.
| Subdirectory | Contents |
|---|---|
/usr/bin |
The main body of user commands |
/usr/sbin |
Admin commands |
/usr/lib |
Shared libraries programs depend on |
/usr/share |
Architecture-independent data (docs, icons, man pages) |
/usr/local |
Software you install manually |
/usr/local is the one to remember: it mirrors /usr (its own bin, lib, share) but is reserved for things you install by hand — compiled from source or grabbed outside the package manager. Keeping them here means a distro upgrade, which rewrites /usr, won't clobber your local installs. It's the polite boundary between "stuff the OS manages" and "stuff I added."
Historical note: /usr originally meant "user" home space, but its role shifted long ago; it's now backronymed "Unix System Resources."