GNU C Library

History

The Glibc project was initially written mostly by Roland McGrath, working for the Free Software Foundation (FSF) in the 1980s.

In February 1988, FSF described glibc as having nearly completed the functionality required by ANSI C. By 1992, it had the ANSI C-1989 and POSIX.1-1990 functions implemented and work was under way on POSIX.2.

In September 1995 Ulrich Drepper made his first contribution to the glibc project and gradually became over the 1990s the core contributor and maintainer of glibc. Drepper held the maintainership position for many years and accumulated until 2012 63% of all commits of the project.

Fork "Linux libc"

In the early 1990s, the developers of the Linux kernel forked glibc. Their fork, called "Linux libc", was maintained separately for years and released versions 2 through 5.

When FSF released glibc 2.0 in January 1997, it had much more complete POSIX standards compliance, better internationalisation and multilingual function, IPv6 capability, 64-bit data access, facilities for multithreaded applications, future version compatibility, and the code was more portable. At this point, the Linux kernel developers discontinued their fork and returned to using FSF's glibc.

The last used version of Linux libc used the internal name (soname) libc.so.5. Following on from this, glibc 2.x on Linux uses the soname libc.so.6 (Alpha and IA64 architectures now use libc.so.6.1, instead). The *.so file name is often abbreviated as libc6 (for example in the package name in Debian) following the normal conventions for libraries.

According to Richard Stallman, the changes that had been made in Linux libc could not be merged back into glibc because the authorship status of that code was unclear and the GNU project is quite strict about recording copyright and authors.

Installation of a steering committee

Starting in 2001 the library's development had been overseen by a committee, with Ulrich Drepper kept as the lead contributor and maintainer. The steering committee installation was surrounded by a public controversy as it was openly described by Ulrich Drepper as a failed hostile takeover maneuver by RMS.

Migrated to Git, a distributed VCS

While previously in a CVS repository, in 2009 glibc was migrated to a Git (a distributed version control system) repository on Sourceware.

Debian switches to EGLIBC and back

After long standing controversies around Drepper's leading style and external contribution acceptance, Debian switched publicly to the glibc fork EGLIBC in 2009, and back with the Debian 8.0 (Jessie) in April 2015.

Steering committee disbands

In March 2012, the steering committee voted to disband itself and remove Drepper in favor of a community-driven development process, with Ryan Arnold, Maxim Kuvyrkov, Joseph Myers, Carlos O'Donell, and Alexandre Oliva holding the responsibility of GNU maintainership (but no extra decision-making power).

After the change in glibc maintainership Debian and other projects migrated back to the glibc, who before switched to alternatives. Also, since the beginning of 2014, the glibc fork EGLIBC is no longer being developed, since its "goals are now being addressed directly in GLIBC".

Version history

For most systems, the version of glibc can be obtained by executing the lib file (for example, /lib/libc.so.6).

Functionality

glibc provides the functionality required by the Single UNIX Specification, POSIX (1c, 1d, and 1j) and some of the functionality required by ISO C11, ISO C99, Berkeley Unix (BSD) interfaces, the System V Interface Definition (SVID) and the X/Open Portability Guide (XPG), Issue 4.2, with all extensions common to XSI (X/Open System Interface) compliant systems along with all X/Open UNIX extensions.

In addition, glibc also provides extensions that have been deemed useful or necessary while developing GNU.

Supported hardware and kernels

Glibc is used in systems that run many different kernels and different hardware architectures. Its most common use is in systems using the Linux kernel on x86 hardware, however, officially supported hardware includes: 32-bit ARM and its newer 64-bit ISA (AArch64), DEC Alpha, PA-RISC, IA-64, Motorola m68k, MicroBlaze, MIPS, Nios II, PowerPC, s390, SPARC, TILE, and x86. It officially supports the Hurd and Linux kernels. Additionally, there are heavily patched versions that run on the kernels of FreeBSD and NetBSD (from which Debian GNU/kFreeBSD and Debian GNU/NetBSD systems are built, respectively), as well as a forked-version of OpenSolaris. It is also used (in an edited form) and named libroot.so in BeOS and Haiku.

Use in small devices

glibc has been criticized as being "bloated" and slower than other libraries in the past, e.g. by Linus Torvalds and embedded Linux programmers. For this reason, several alternative C standard libraries have been created which emphasize a smaller footprint. However, many small-device projects use GNU libc over the smaller alternatives because of its application support, standards compliance, and completeness. Examples include Openmoko and Familiar Linux for iPaq handhelds (when using the GPE display software).

Compatibility layers

There are compatibility layers ("shims") to allow programs written for other ecosystems, e.g. Google's Android and Microsoft's Windows, to run on glibc interface offering systems. libhybris is a compatibility layer for Android's Bionic and Wine can be also seen as compatibility layer from Win32 API/ABI to glibc.