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libc.7: New page giving brief overview of C libraries on Linux
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH LIBC 7 2009-01-13 "Linux" "Linux Programmer's Manual"
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.SH NAME
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libc \- Overview of standard C libraries on Linux
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.SH DESCRIPTION
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The term "libc" is commonly used as a shorthand for
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the "standard C library",
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a library of standard functions that can be used by all C programs
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(and sometimes by programs in other languages).
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Because of some history (see below), use of the term "libc"
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to refer to the standard C library is somewhat ambiguous on Linux.
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.SS glibc
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By far the most widely used C library on Linux is the GNU C Library
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.RI ( http://www.gnu.org/software/libc/ ),
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often referred to as
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.IR glibc .
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This is the C library that is nowadays used in all
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major Linux distributions.
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It is also the C library whose details are documented
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in the relevant pages of the
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.I man-pages
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project (primarily in Section 3 of the manual).
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Documentation of glibc is also available in the glibc manual,
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available via the command
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.IR "info libc" .
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Release 1.0 of glibc was made in September 1992.
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(There were earlier 0.x releases.)
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The next major release of glibc was 2.0, at the beginning of 1997.
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The pathname
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.I /lib/libc.so.6
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(or something similar) is normally a symbolic link that
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points to the location of the glibc library,
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and executing this pathname will cause glibc to display
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various information about the version installed on your system.
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.SS Linux libc
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In the early to mid 1990s, there was for a while
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.IR "Linux libc" ,
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a fork of glibc 1.x created by Linux developers who felt that glibc
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development at the time was not sufficing for the needs of Linux.
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Often, this library was referred to (ambiguously) as just "libc".
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Linux libc released major versions 2, 3, 4, and 5
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(as well as many minor versions of those releases).
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For a while,
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Linux libc was the standard C library in many Linux distributions.
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However, notwithstanding the original motivations of the Linux libc effort,
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by the time glibc 2.0 was released, it was clearly superior to Linux libc,
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and all major Linux distributions that had been using Linux libc
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soon switched back to glibc.
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(Since this switch occurred over a decade ago,
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.I man-pages
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no longer takes care to document Linux libc details.
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Nevertheless, the history is visible in vestiges of information
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about Linux libc that remain in some manual pages,
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in particular, references to
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.IR libc4
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and
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.IR libc5 .)
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.SS Other C libraries
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There are various other less widely used C libraries for Linux.
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These libraries are generally smaller than glibc,
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both in terms of features and memory footprint,
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and often intended for building small binaries,
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perhaps targeted at development for embedded Linux systems.
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Among such libraries are
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.I uClibc
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.RI ( http://www.uclibc.org/ )
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and
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.I dietlibc
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.RI ( http://www.fefe.de/dietlibc ).
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Details of these libraries are generally not covered by the
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.I man-pages
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project.
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.SH SEE ALSO
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.\" FIXME add SEE ALSO entries from the following pages:
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.BR syscalls (2),
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.BR feature_test_macros (7),
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.BR man-pages (7),
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.BR standards (7)
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