# /usr
**/usr** is the secondary hierarchy and holds the bulk of the system's installed software. On a fresh install the majority of disk space under `/` is consumed by `/usr`. It mirrors the top-level structure: `/usr/bin` for user binaries, `/usr/lib` for libraries, `/usr/sbin` for admin tools, `/usr/share` for architecture-independent data, and `/usr/include` for C header files. The constraint that applies to `/bin` and `/lib` (must be available before other filesystems mount) does not apply here: `/usr` can be a separate partition or even a network mount.

```
/usr/bin/           all user-facing binaries not needed during early boot
/usr/sbin/          all admin binaries not needed during early boot
/usr/lib/           shared libraries for /usr/bin and /usr/sbin
/usr/include/       C and C++ header files (installed by -dev packages)
/usr/share/         architecture-independent data: man pages, icons, locale data
/usr/share/man/     manual pages
/usr/share/doc/     package documentation
/usr/local/         locally installed software, outside the package manager
/usr/local/bin/     binaries installed by the local administrator
```

`/usr/local/` is reserved for software installed by the sysadmin rather than the distribution's package manager. It has the same subdirectory layout (`bin/`, `lib/`, `include/`, `share/`) and by convention takes precedence in `$PATH` over `/usr/bin`. Installing a custom build of a tool to `/usr/local/bin` overrides the system version without modifying anything the package manager owns.

On distributions with merged `/usr`, the top-level `/bin`, `/lib`, and `/sbin` are symlinks into `/usr`, making `/usr/bin` the single authoritative location for all binaries.