GNU C Library

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++. It was started in the early 1990s by the Free Software Foundation for their GNU operating system.
Released under the GNU Lesser General Public License, glibc is free software. The GNU C Library project provides the core libraries for the GNU system and GNU/Linux systems, as well as many other systems that use Linux as the kernel. These libraries provide critical APIs including ISO C11, POSIX.1-2008, BSD, OS-specific APIs and more. These APIs include such foundational facilities as open, read, write, malloc, printf, getaddrinfo, dlopen, pthread_create, crypt, login, exit and more.


The glibc project was initially written mostly by Roland McGrath, working for the Free Software Foundation in the 1980s as a teenager.
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 over the 1990s gradually became the core contributor and maintainer of glibc. Drepper held the maintainership position for many years and until 2012 accumulated 63% of all commits to the project.

Linux libc

In the early 1990s, the developers of the Linux kernel forked glibc. Their fork, "Linux libc", was maintained separately.
When the FSF released glibc 2.0 in January 1997, the kernel developers discontinued Linux libc due to glibc 2.0’s superior compliance with POSIX standards. glibc 2.0 also had better internationalisation and more in-depth translation, IPv6 capability, 64-bit data access, facilities for multithreaded applications, future version compatibility, and the code was more portable.
The last-used version of Linux libc used the internal name Following on from this, glibc 2.x on Linux uses the soname The *.so file name is often abbreviated as libc6 following the normal conventions for libraries.
According to Richard Stallman, the FSF could not merge the changes made in Linux libc into glibc due to vague authorship. 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 Richard Stallman.

Migrated to Git, a distributed VCS

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

Debian switches to EGLIBC and back

After longstanding controversies around Drepper's leadership style and external contribution acceptance, Debian switched publicly to the glibc fork EGLIBC in 2009, and back with the Debian 8.0 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.
After the change in glibc maintainership, Debian and other projects that had switched to alternatives migrated back to glibc. From the beginning of 2014, the glibc fork EGLIBC is no longer being developed since its "goals are now being addressed directly in GLIBC".
In July 2017, 30 years after he started glibc, Roland McGrath announced his departure, "declaring myself maintainer emeritus and withdrawing from direct involvement in the project. These past several months, if not the last few years, have proven that you don't need me any more".

Version history

For most systems, the version of glibc can be obtained by executing the lib file.
0.1 – 0.6October 1991 – February 1992
1.0February 1992
1.01 – 1.09.3March 1992 – December 1994
1.90 – 1.102May 1996 – January 1997
2.0January 1997
2.0.1January 1997
2.0.2February 1997
2.0.91December 1997
2.0.95July 1998
2.1February 1999
2.1.1March 1999
2.2November 2000
2.2.1January 2001
2.2.2February 2001
2.2.3March 2001
2.2.4July 2001
2.3October 2002
2.3.1October 2002
2.3.2February 2003Debian 3.1
2.3.3December 2003
2.3.4December 2004Standard for Linux Standard Base 3.0RHEL 4
2.3.5April 2005SLES 9
2.3.6November 2005Debian 4.0
2.4March 2006Standard for LSB 4.0, initial inotify supportSLES 10
2.5September 2006Full inotify supportRHEL 5
2.6May 2007
2.7October 2007Debian 5, Ubuntu 8.04
2.8April 2008
2.9November 2008
2.10May 2009
2.11October 2009SLES 11, Ubuntu 10.04, eglibc used in Debian 6
2.12May 2010RHEL 6
2.13January 2011eglibc 2.13 used in Debian 7
2.14June 2011
2.15March 2012Ubuntu 12.04 and 12.10
2.16June 2012x32 ABI support, ISO C11 compliance, SystemTap
2.17December 201264-bit ARM supportUbuntu 13.04, RHEL 7
2.18August 2013Improved C++11 support. Support for Intel TSX lock elision. Support for the Xilinx MicroBlaze and IBM POWER8 microarchitectures.Fedora 20
2.19February 2014SystemTap probes for malloc. GNU Indirect Function 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, openSUSE 13, SLES 12
2.20September 2014Support for file description locksFedora 21
2.21February 2015New semaphore implementationUbuntu 15.04, Fedora 22
2.22August 2015Support to enable Google Native Client, that originally ran on x86, running on ARMv7-A, Unicode 7.0Fedora 23
2.23February 2016Unicode 8.0Fedora 24, Ubuntu 16.04
2.24August 2016Some deprecated features have been removedFedora 25, Ubuntu 16.10 and 17.04, Debian 9
2.25February 2017The getentropy and getrandom functions, and the header file have been added.Fedora 26
2.26August 2017Improved performance, Unicode 10 supportFedora 27, Ubuntu 17.10
2.27February 2018Performance optimizations. RISC-V support.Fedora 28, Ubuntu 18.04
2.28August 2018statx, renameat2, Unicode 11.0.0Ubuntu 18.10, RHEL 8.0.0, Debian 10, Fedora 29
2.29February 2019
  • getcpu wrapper
  • build and install all locales as directories with files
  • optimized trigonomical functions
  • Transactional Lock Elision for powercp64le ABI
  • posix_spawn_file_actions_addchdir_np and posix_spawn_file_actions_addfchdir_np
  • popen and system do not run atfork handlers anymore
  • support for the C-SKY ABIV2 running on Linux
  • strftime's default formatting of a locale's alternative year; the '_' and '-' flags can now be applied to its "%EY"
Ubuntu 19.04, Fedora 30
2.30August 2019Unicode 12.1.0, the dynamic linker accepts the --preload argument to preload shared objects, the gettid function has been added on Linux, Minguo calendar support, new Japanese era added to ja_JP locale, memory allocation functions fail with total object size larger than PTRDIFF_MAX; fixedUbuntu 19.10, Fedora 31
2.31February 2020Initial C2x standard supportUbuntu 20.04, Fedora 32


glibc provides the functionality required by the Single UNIX Specification, POSIX and some of the functionality required by ISO C11, ISO C99, Berkeley Unix interfaces, the System V Interface Definition and the X/Open Portability Guide, Issue 4.2, with all extensions common to XSI 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, C-SKY, DEC Alpha, IA-64, Motorola m68k, MicroBlaze, MIPS, Nios II, PA-RISC, PowerPC, RISC-V, s390, SPARC, 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, as well as a forked-version of OpenSolaris. It is also used and named 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.

Compatibility layers

There are compatibility layers to allow programs written for other ecosystems to run on glibc interface offering systems. These include libhybris, a compatibility layer for Android's Bionic, and Wine, which can be seen as compatibility layer from Windows APIs to glibc and other native APIs available on Unix-like systems.