libc — overview of standard C libraries on Linux
The term "libc" is commonly used as a shorthand for the "standard C library", a library of standard functions that can be used by all C programs (and sometimes by programs in other languages). Because of some history (see below), use of the term "libc" to refer to the standard C library is somewhat ambiguous on Linux.
By far the most widely used C library on Linux is the
GNU C Library http://www.gnu.org/software/libc/ often referred
to as glibc. This
is the C library that is nowadays used in all major Linux
distributions. It is also the C library whose details are
documented in the relevant pages of the man-pages project
(primarily in Section 3 of the manual). Documentation of
glibc is also available in the glibc manual, available via
the command info
libc. Release 1.0 of glibc was made in
September 1992. (There were earlier 0.x releases.) The next
major release of glibc was 2.0, at the beginning of
1997.
The pathname /lib/libc.so.6 (or something similar) is
normally a symbolic link that points to the location of the
glibc library, and executing this pathname will cause glibc
to display various information about the version installed
on your system.
In the early to mid 1990s, there was for a while Linux libc, a fork of glibc 1.x created by Linux developers who felt that glibc development at the time was not sufficing for the needs of Linux. Often, this library was referred to (ambiguously) as just "libc". Linux libc released major versions 2, 3, 4, and 5 (as well as many minor versions of those releases). For a while, Linux libc was the standard C library in many Linux distributions.
However, notwithstanding the original motivations of the
Linux libc effort, by the time glibc 2.0 was released (in
1997), it was clearly superior to Linux libc, and all major
Linux distributions that had been using Linux libc soon
switched back to glibc. Since this switch occurred long
ago, man-pages no
longer takes care to document Linux libc details.
Nevertheless, the history is visible in vestiges of
information about Linux libc that remain in some manual
pages, in particular, references to libc4 and libc5.
There are various other less widely used C libraries for
Linux. These libraries are generally smaller than glibc,
both in terms of features and memory footprint, and often
intended for building small binaries, perhaps targeted at
development for embedded Linux systems. Among such
libraries are uClibc
http://www.uclibc.org/ dietlibc
http://www.uclibc.org/ and musl libc
http://www.musl-libc.org/ Details of these libraries
are covered by the man-pages project, where
they are known.
syscalls(2), getauxval(3), proc(5), feature_test_macros(7), man-pages(7), standards(7), vdso(7)
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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