musl

Musl is a free and open-source implementation of the standard C library for Linux-based operating systems. It is designed to be lightweight, fast, clean, and correct, providing the facilities defined by the ISO C standard and POSIX while avoiding unnecessary complexity found in some other libc implementations. Developed primarily by Rich Felker and contributors, musl originated in the early 2000s and has since become a popular choice for minimalist and security-focused Linux distributions.

Musl emphasizes correctness and portability over feature bloat. Its codebase aims for readable, well-structured code and strict conformance to standards, with an emphasis on predictable behavior across architectures. It provides the standard C library components for input/output, memory management, strings, time, locale handling, threading interfaces, signal handling, and dynamic linking support. The project is designed to be friendly to static linking, enabling small, statically linked binaries.

The library is released under a permissive free software license, commonly described as akin to MIT-style terms. It is adopted by several Linux distributions and communities, most notably Alpine Linux and Void Linux, and supports a wide range of architectures, including x86-64, x86, ARM, and others. While musl aims for POSIX and ISO C compatibility, it is not a universal drop-in replacement for glibc; programs compiled against glibc typically need to be rebuilt or adjusted to run with musl, as some glibc-specific extensions may be unavailable.

See also: glibc, libc, Alpine Linux, musl-tools.