The /usr hierarchy is for vendor supplied Operating System resources.
Except for the /usr/local
hierarchy, nothing should modify anything
under /usr except the OS package manager.
Software applications must assume that /usr can be read-only.
The /usr hierarchy must not be used for volitile data.
Except for
/usr/local,
the /usr hierarchy must not be used for any data that is added
or changed outside of package installation/removal as done by the OS package manager.
The OS package manager may assume that all of the /usr hierarchy
(except
/usr/local)
is the same mountpoint.
Software being installed outside of the OS package manager should not store
data in /usr as this may impede any future invocation
of the OS package manager. The
/usr/local
hierarchy is the exception, and is reserved for software outside of the OS
package manager.
/usr/bin (Executables)
Executable files which should appear in the standard search $PATH, and
are useful to invoke from a shell. Daemons and executables which are not useful
to invoke from a shell instead live in /usr/lib or
/usr/libexec.
/usr/include (C/C++ Headers)
The /usr/include directory contains C and C++ header files,
usually contained in packages with the -devel suffix.
/usr/lib and /usr/lib64 (Shared libraries)
On Amazon Linux 2023, the /usr/lib64 path is used for
64-bit shared libraries, and package data which is architecture dependent.
Since AL2023 does not ship with any 32-bit userspace support, there
are only 64-bit shared libraries available.
The /usr/lib path is for static data from OS packages
which is compatible with all architectures. This may include executables
not usually invoked from a shell, which may also be found in
/usr/libexec. Shared libraries are found in
/usr/lib64 rather than /usr/lib.
/usr/local (System administrator installed software)
On Amazon Linux 2023, the /usr/local path is available
for the system administrator to install software in, software that is
not owned by the OS, and will not be touched by the OS. The default
/usr/local hierarchy mirrors the /
hierarchy.
/usr/share (Shared resources)
Shared resources such as documentation, fonts, and time zone data live in /usr/share.
It is common for various specifications to dictate exactly where and in what format data is stored in
this directory.
/usr/share/doc (Documentation)
Documentation that comes with packages will be stored in /usr/share/doc.
