usr

usr is a standard top-level directory in Unix-like operating systems. Historically, it was intended to hold the majority of user-level programs and data separate from the files needed to boot and repair the system. In many modern distributions, /usr contains the bulk of installed applications, libraries, and associated data, while the root directory / contains only the essential components required to boot the system.

Contents typically found under /usr include a number of well-known subdirectories. /usr/bin stores user commands and utilities that are not required for initial system boot. /usr/sbin contains system administration tools that are not needed by regular users. /usr/lib and /usr/lib64 hold libraries used by binaries in /usr/bin and elsewhere. /usr/include contains header files used by compilers and development tools. /usr/share houses architecture-independent data such as documentation, shared data files, and locale information. /usr/local is intended for software installed locally by the system administrator, separate from the distribution’s package manager. /usr/src often contains source code for the system or installed software. Other common components include /usr/share/man for manual pages and /usr/libexec for helper binaries used by other programs.

Origin of the name usr is disputed. Some sources say it stands for Unix System Resources, others contend it means User. The term dates from early Unix, reflecting the intended division between core boot and maintenance components and the broader, user-facing software environment. The exact layout and practices surrounding /usr have evolved across Unix, BSD, Linux, and macOS systems. Today, /usr remains a large, shared directory in many installations, though its exact role and structure can vary by operating system and distribution.