musl was designed from scratch to allow efficient static linking and to have realtime-quality robustness by avoiding race conditions, internal failures on resource exhaustion, and various other bad worst-case behaviors present in existing implementations.[4] The dynamic runtime is a single file with stable ABI allowing race-free updates and the static linking support allows an application to be deployed as a single portable binary without significant size overhead.
It claims compatibility with the POSIX 2008 specification and the C11 standard. It also implements most of the widely used non-standard Linux, BSD, and glibc functions.[5] There is partial ABI compatibility with the part of glibc required by Linux Standard Base.[6]
Version 1.2.0 has support for (no longer current) Unicode 12.1.0 (while still having full UTF-8 support,[7] more conformant/strict than glibc), and version 1.2.1 "features the new 'mallocng' malloc implementation, replacing musl's original dlmalloc-like allocator that suffered from fundamental design problems."[2]
Use
Linux distributions which use musl as their standard C library (some use only musl) include but are not limited to: