musl is a C standard library intended for

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s based on the

Linux kernel The Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel. It was originally authored in 1991 by Linus Torvalds for his i386-based PC, and it was soon adopted as the kernel for the GNU ope ...

, released under the

MIT License The MIT License is a permissive free software license originating at the Massachusetts Institute of Technology (MIT) in the late 1980s. As a permissive license, it puts only very limited restriction on reuse and has, therefore, high license comp ...

. It was developed by Rich Felker with the goal to write a clean, efficient and standards-conformant libc implementation.

Overview

musl was designed from scratch to allow efficient

static linking In computer science, a static library or statically-linked library is a set of routines, external functions and variables which are resolved in a caller at compile-time and copied into a target application by a compiler, linker, or binder, produci ...

and to have realtime-quality robustness by avoiding

race conditions A race condition or race hazard is the condition of an electronics, software, or other system where the system's substantive behavior is dependent on the sequence or timing of other uncontrollable events. It becomes a bug when one or more of ...

, internal failures on resource exhaustion and various other bad worst-case behaviors present in existing implementations. 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 The Portable Operating System Interface (POSIX) is a family of standards specified by the IEEE Computer Society for maintaining compatibility between operating systems. POSIX defines both the system- and user-level application programming interf ...

2008 specification and the

C11 C11, C.XI, C-11 or C.11 may refer to: Transport * C-11 Fleetster, a 1920s American light transport aircraft for use of the United States Assistant Secretary of War * Fokker C.XI, a 1935 Dutch reconnaissance seaplane * LET C-11, a license-build var ...

standard. It also implements most of the widely used non-standard

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

BSD The Berkeley Software Distribution or Berkeley Standard Distribution (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berk ...

, and

glibc The GNU C Library, commonly known as glibc, is the GNU Project's implementation of the C standard library. Despite its name, it now also directly supports C++ (and, indirectly, other programming languages). It was started in the 1980s by ...

functions. There is partial ABI compatibility with the part of glibc required by

Linux Standard Base The Linux Standard Base (LSB) was a joint project by several Linux distributions under the organizational structure of the Linux Foundation to standardize the software system structure, including the Filesystem Hierarchy Standard used in the ...

. Version 1.2.0 has support for (no longer current)

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology Technical standard, standard for the consistent character encoding, encoding, representation, and handling of Character (computing), text expre ...

12.1.0 (while still having full

UTF-8 UTF-8 is a variable-width encoding, variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit'' ...

support, more conformant/strict than

), and version 1.2.1 "features the new 'mallocng'

malloc C dynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely , , , and . The C++ programming language includes ...

implementation, replacing musl's original

dlmalloc C dynamic memory allocation refers to performing manual memory management for dynamic memory allocation in the C programming language via a group of functions in the C standard library, namely , , , and . The C++ programming language includes ...

-like allocator that suffered from fundamental design problems."

Use

Some

Linux distribution A Linux distribution (often abbreviated as distro) is an operating system made from a software collection that includes the Linux kernel and, often, a package management system. Linux users usually obtain their operating system by downloading one ...

s that can use musl as the standard C library include

Alpine Linux Alpine Linux is a Linux distribution designed to be small, simple and secure. Alpine Linux uses musl, BusyBox and OpenRC instead of the more commonly used glibc, GNU Core Utilities and systemd respectively.

, Dragora 3,

Gentoo Linux Gentoo Linux (pronounced ) is a Linux distribution built using the Portage package management system. Unlike a binary software distribution, the source code is compiled locally according to the user's preferences and is often optimized for the ...

OpenWrt OpenWrt (from ''open wireless router'') is an open-source project for embedded operating systems based on Linux, primarily used on embedded devices to route network traffic. The main components are Linux, util-linux, musl, and BusyBox. All com ...

, Sabotage, Morpheus Linux and

Void Linux Void Linux is an independent Linux distribution that uses the X Binary Package System (XBPS) package manager, which was designed and implemented from scratch, and the runit init system. Excluding binary blobs, binary kernel blobs, a base install i ...

. The

seL4 L4 is a family of second-generation microkernels, used to implement a variety of types of operating systems (OS), though mostly for Unix-like, ''Portable Operating System Interface'' (POSIX) compliant types. L4, like its predecessor microkernel ...

microkernel ships with musl. For binaries that have been linked against glibc, gcompat can be used to execute them on musl-based distros.

References

External links

*
Comparison of C/POSIX standard library implementations for Linux

Matrix of C/POSIX standard libraries by architecture

Project:Hardened musl on Gentoo wiki
* Rich Felker held a talk at the Embedded Linux Conference (ELC) 2015
ELC 2015 - Transitioning From uclibc to musl for Embedded Development - Rich Felker, Openwall
{{CProLang C standard library Free computer libraries Free software programmed in C Interfaces of the Linux kernel Linux APIs Software using the MIT license

Overview

Use

See also

References

External links