musl - standard C library

Introduction

musl provides consistent quality and implementation behavior from tiny embedded systems to full-fledged servers. Minimal machine-specific code means less chance of breakage on minority architectures and better success with “write once run everywhere” C development.

musl's efficiency is unparalleled in Linux libc implementations. Designed from the ground up for static linking, musl carefully avoids pulling in large amounts of code or data that the application will not use. Dynamic linking is also efficient; by integrating the entire standard library implementation, including threads, math, and even the dynamic linker itself into a single shared object, most of the startup time and memory overhead of dynamic linking have been eliminated.

musl features the first post-NPTL implementation of POSIX threads for Linux, and the first aimed at complete conformance and robustness. Thread cancellation has been re-designed to avoid serious race conditions in the original NPTL design. As for efficiency, the whole threads implementation weighs in at around 10-20k depending on target architecture and compiler settings.

Not only the threads implementation, but all code in musl has been designed for realtime-quality robustness. Low-memory or resource exhaustion conditions are never fatal. musl has no unnecessary dynamic allocation and no unrecoverable late failures. All error conditions can be detected and handled by applications; interfaces for which an application could not reasonably handle failure do not fail.

Using musl maximizes application deployability. Its permissive MIT license is compatible with all FOSS licenses, static-linking-friendly, and makes commercial use painless too. Binaries statically linked with musl have no external dependencies, even for features like DNS lookups or character set conversions that are implemented with dynamic loading on glibc. An application can really be deployed as a single binary file and run on any machine with the appropriate instruction set architecture and Linux kernel or Linux syscall ABI emulation layer.

Finally, musl has simple source code and source tree layout, so it’s easy to customize or track down the cause of unexpected behavior or bugs, or simply learn how the library works.

Please see the http://www.musl-libc.org/ page for more information.

Installing and Testing

musl is included in Debian since Jessie (8).

For further package information see https://tracker.debian.org/pkg/musl

Installation

To install musl run:

# apt-get update
# apt-get install musl

This will install the musl runtime but will not install any development packages. If you are a developer and/or want to compile simple C99 based programs, please have also a look at the packages musl-dev and musl-tools.

Configuring

The musl runtime uses a similiar aproach for configuring shared library paths as glibc. If you want to add your library in a non standard path, please add a config file under /etc/ld-musl-$ARCH.d/ containing your custom path. After that you can run:

# ld-musl-config

Please note that it requires root privileges to do so. For additional information see the manpage to ld-musl-config.

There are other options available to influence the musl libc dynamic loader. Full documentation can be found under http://www.musl-libc.org/doc/1.0.0/manual.html. In particular the variable TZ, LD_PRELOAD and LD_LIBRARY_PATH might be of intrest.

To limit the influence of a variable to a single binary, use something like:

# LD_PRELOAD=$PWD/yourlib.so ./yourbin

Use it

Select a compiler

musl-gcc

t.b.d.

musl-cross

t.b.d.

Use cases

Static compiled admin binaries

t.b.d.

Fast static C CGI Scripts

t.b.d.

Embedded Linux

t.b.d. ... and mor t.b.d.