The GNU C Library, commonly known as glibc, is the GNU Project implementation of the C standard library. It provides a wrapper around the system calls of the Linux kernel and other kernels for application use. Despite its name, it now also directly supports C++ (and, indirectly, other programming languages). It was started in the 1980s by the Free Software Foundation (FSF) for the GNU operating system.
glibc is free software released under the GNU Lesser General Public License.
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| 2.30 || August 2019 || Unicode 12.1.0, the dynamic linker accepts the <code>--preload</code> argument to preload shared objects, the <code>gettid</code> function has been added on Linux, Minguo (Republic of China) calendar support, new Japanese era added to ja_JP locale, memory allocation functions fail with total object size larger than <code>PTRDIFF_MAX</code>; fixed
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| 2.31 || February 2020 || Initial C23 standard support
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| 2.32 || August 2020 || Unicode 13.0, 'access' attribute for better warnings in GCC 10, i.e. to "help detect buffer overflows and other out-of-bounds accesses"
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| 2.33 || February 2021 || HWCAPS
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| 2.34 || August 2021 || libpthread, libdl, libutil, libanl has been integrated into libc.
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| 2.35 || February 2022 || Unicode 14.0, C.UTF-8 locale, restartable sequences. Removed Intel MPX support.
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| 2.36 || August 2022 ||
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| 2.37 || February 2023 || Unicode 15.0
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| 2.38 || August 2023 || The strlcpy and strlcat functions added. libmvec support for ARM64.
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| 2.39 || January 2024 || The stdbit.h header has been added from ISO C2X. Support for shadow stacks on x86_64, new security features, and the removal of libcrypt.
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| 2.40 || July 2024 || Partial support for the ISO C23 standard, a new tunable for the testing of programs, improved 64-bit ARM vector support.
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| 2.41 || January 2025 || Add , , functions. Unicode 16.0
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| 2.42 || July 2025 || New math functions, support for arbitrary baud rates in the termios.h interface, SFrame-based stack tracing.
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| 2.43 || January 2026 || Unicode 17.0, more C23 support, openat2 and mseal on Linux, experimental Clang support
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thumb|Ulrich Drepper in 2007, the main author of glibc
thumb|The GNU C Library is a wrapper around the [[system calls of the Linux kernel.]]
thumb|The [[Linux kernel and GNU C Library together form the Linux API. After compilation, the binaries offer an ABI.]]
The glibc project was initially written mostly by Roland McGrath, working for the Free Software Foundation (FSF) in the summer of 1987 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 and by 1997 most commits were made by him. Drepper held the maintainership position for many years and until 2012 accumulated 63% of all commits to the project.
In May 2009, glibc was migrated to a Git repository.
In 2014, glibc suffered from an ABI breakage bug on s390.
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 anymore".
In 2021, the copyright assignment requirement to the Free Software Foundation was removed from the project.
Fork and variant<span class="anchor" id="Linux libc"></span>
In 1994, the developers of the Linux kernel forked glibc. Their fork, "Linux libc", was maintained separately until around 1998. Because the copyright attribution was insufficient, changes could not be merged back to the GNU Libc. 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 internationalization 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 (soname) . Following on from this, glibc 2.x on Linux uses the soname
In 2009, Debian and a number of derivatives switched from glibc to the variant eglibc. Eglibc was supported by a consortium consisting of Freescale, MIPS, MontaVista and Wind River. It contained changes that made it more suitable for embedded usage and had added support for architectures that were not supported by glibc, such as the PowerPC e500. The code of eglibc was merged back into glibc at version 2.20. Since 2014, eglibc is discontinued. The Yocto Project and Debian also moved back to glibc since the release of Debian Jessie.
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.
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).
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: ARM, ARC, C-SKY, DEC Alpha, IA-64, Motorola m68k, MicroBlaze, MIPS, Nios II, PA-RISC<!--"hppa"-->, PowerPC, RISC-V, s390, SPARC, and x86 (old versions support TILE). 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 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).
Secure string functions
glibc does not implement bounds-checking interfaces defined in C11 and did not implement strlcpy and strlcat until 2023 on the grounds that "in practice these functions can cause trouble, as their intended use encourages silent data truncation, adds complexity and inefficiency, and does not prevent all buffer overruns in the destinations." The FAQ pointed out that the bounds-checking interfaces were optional in the ISO standard and that snprintf was available as an alternative.