GNU C Library

"glibc" redirects here. It is not to be confused with GLib or Gnulib.

GNU C Library

Original author(s)	Roland McGrath
Developer(s)	GNU Project
Initial release	1987 (1987)
Stable release	2.23 (February 19, 2016 (2016-02-19)) [±]
Development status	Active
Written in	C
Operating system	Unix-like
Type	Runtime library
License	GNU Lesser General Public License
Website	www.gnu.org/software/libc/

The Linux API is composed out of the System Call Interface of the Linux kernel, the GNU C Library (by GNU), libdrm, libalsa and libevdev (by freedesktop.org).

The GNU C Library is a wrapper around the system calls of the Linux kernel.

The Linux kernel and GNU C Library together form the Linux API. After compilation, the binaries offer an ABI.

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 early 1990s by the Free Software Foundation (FSF) for their GNU operating system.

Released under the GNU Lesser General Public License, glibc is free software.

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 did his first contribution to the glibc project and gradually became over the 1990s the core contributor and maintainer of glibc. Drepper hold 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 failed hostile takeover maneuver by RMS.

Switch to git

While before in a CVS repository, in 2009 glibc was migrated to a Git repository on Sourceware.

Debian switches to EGLIBC

After long standing controversies around Drepper's leading style and external contribution acceptance, Debian switched publicly to the glibc fork EGLIBC in 2009.

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).

Version	Date	Notes	Adoption
0.1 – 0.6	Oct 1991 – February 1992
1.0	February 1992
1.01 – 1.09.3	March 1992 – December 1994
1.90 – 1.102	May 1996 – January 1997
2.0	January 1997
2.0.1	January 1997
2.0.2	February 1997
2.0.91	December 1997
2.0.95	July 1998
2.1	February 1999
2.1.1	March 1999
2.2	November 2000
2.2.1	January 2001
2.2.2	February 2001
2.2.3	March 2001
2.2.4	July 2001
2.3	October 2002
2.3.1	October 2002
2.3.2	February 2003		Debian 3.1 (Sarge)
2.3.3	December 2003
2.3.4	December 2004	Standard for Linux Standard Base (LSB) 3.0	RHEL 4 (Update 5)
2.3.5	April 2005		SLES 9
2.3.6	November 2005		Debian 4.0 (Etch)
2.4	March 2006	Standard for LSB 4.0, initial inotify support	SLES 10
2.5	September 2006	Full inotify support	RHEL 5
2.6	May 2007
2.7	October 2007		Debian 5 (Lenny), Ubuntu 8.04
2.8	April 2008
2.9	November 2008
2.10	May 2009
2.11	October 2009		SLES 11, Ubuntu 10.04, eglibc used in Debian 6 (Squeeze)
2.12	May 2010		RHEL 6
2.13	January 2011		eglibc 2.13 used in Debian 7 (Wheezy)
2.14	June 2011
2.15	March 2012		Ubuntu 12.04 and 12.10
2.16	June 2012	x32 ABI support, ISO C11 compliance, SystemTap
2.17	December 2012	64-bit ARM support	Ubuntu 13.04, RHEL 7
2.18	August 2013	Improved C++11 support. Support for Intel TSX lock elision. Support for the Xilinx MicroBlaze and IBM POWER8 microarchitectures.	Fedora 20
2.19	February 2014	SystemTap probes for malloc. GNU Indirect Function (IFUNC) support for ppc32 and ppc64. New feature test macro _DEFAULT_SOURCE to replace _SVID_SOURCE and _BSD_SOURCE. Preliminary safety documentation for all functions in the manual. ABI change in ucontext and jmp_buf for s390/s390x.	Ubuntu 14.04, eglibc 2.19 used in Debian 8 (Jessie)
2.20	September 2014	Support for file description locks	Fedora 21
2.21	February 2015	New semaphore implementation	Ubuntu 15.04, Debian experimental, Fedora 22
2.22	August 2015	Google Native Client (NaCl) for running on ARMv7-A, Unicode 7.0	Fedora 23

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: AArch64, ARM, 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. Alternative libcs are Bionic (based mostly on libc from BSD and used in Android), dietlibc, uClibc, Newlib, Klibc, and musl.

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).

Alternatives

Other C standard libraries as alternative to the GNU C Library are for instance: Bionic libc, dietlibc, EGLIBC, klibc, musl, Newlib, and uClibc.

See also

• Gnulib
• libhybris
• Linux kernel API

External links

• GNU libc homepage
• GNU libc developers' page