RPATH

RPATH is a runtime library search path embedded in an executable or shared library on many Unix-like systems. It tells the dynamic linker where to look for required shared libraries when the program starts. The path information is added at link time via the linker option -rpath (for example, -Wl,-rpath,/opt/mylib/lib) and is stored in the executable’s dynamic section as DT_RPATH or DT_RUNPATH.

In ELF binaries, DT_RUNPATH is the modern field, while DT_RPATH is the older one. When both may be present, runtimes generally prefer RUNPATH for compatibility with environment overrides. In practice, a binary with an RPATH or RUNPATH cause the dynamic linker to search those directories before, or as part of, the standard system library paths, affecting how dependencies are resolved at startup.

RPATH is often considered less flexible than RUNPATH for relocatable installations. RUNPATH is generally favored because it allows environment variables, notably LD_LIBRARY_PATH, to influence the search order, making it easier to adapt a binary to different environments without rebuilding it.

A common technique to improve relocatability is to use relative paths, such as $ORIGIN, which expands to the directory containing the executable. For example, -Wl,-rpath,'$ORIGIN/../lib' makes the runtime search relative to the binary’s location.

Security and portability considerations apply: embedding absolute paths can hinder relocation and may complicate packaging or updates. When possible, use RUNPATH with relative paths or rely on system library locations and packaging mechanisms to manage dependencies. LD_LIBRARY_PATH can alter search behavior at runtime, depending on the system and linker configuration.