usrlib

Usrlib refers to the /usr/lib directory in Unix-like operating systems, a standard location for architecture-dependent libraries used by user-space programs. It is part of the /usr hierarchy and is distinct from /lib and from /usr/share, which holds architecture-neutral data.

The directory’s primary purpose is to store runtime libraries that programs link to when they run. These include dynamically linked libraries (commonly with the .so extension on Linux and .dylib on macOS) and, in some cases, static libraries (.a). Many distributions also place language runtimes, plugins, and vendor-specific modules in /usr/lib. To accommodate multiple architectures, there are often architecture-specific subdirectories under /usr/lib, such as /usr/lib/x86_64-linux-gnu or /usr/lib64 on certain systems.

The system dynamic linker/loader uses /usr/lib as part of its search path for locating libraries at runtime, alongside /lib and other architecture-specific directories. Search paths can be influenced by environment variables like LD_LIBRARY_PATH or by configuration files such as /etc/ld.so.conf. Software packages typically install libraries into /usr/lib, and may expose multiple versions via symbolic links (for example, libfoo.so.1 pointing to a concrete version).

Variations exist across systems. Linux distributions differ in their layout and naming conventions for multi-arch support: Debian-based systems commonly use multi-arch directories under /usr/lib, while some Red Hat–based systems use /usr/lib64 for 64-bit libraries. macOS uses /usr/lib as part of a distinct system library model, with libraries located in various system paths.

In summary, /usr/lib is a central repository for architecture-dependent libraries that support the execution of user-space programs, managed by the system’s package manager and organized to handle multiple architectures.