[thirdparty/man-pages.git] / man7 / libc.7

.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.com>
.\"
.\" %%%LICENSE_START(verbatim)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one.
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date.  The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein.  The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\" %%%LICENSE_END
.\"
.TH LIBC 7 2012-08-05 "Linux" "Linux Programmer's Manual"
.SH NAME
libc \- overview of standard C libraries on Linux
.SH DESCRIPTION
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.
.SS glibc
By far the most widely used C library on Linux is the GNU C Library
.UR http://www.gnu.org\:/software\:/libc/
.UE ,
often referred to as
.IR 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
.I man-pages
project (primarily in Section 3 of the manual).
Documentation of glibc is also available in the glibc manual,
available via the command
.IR "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
.I /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.
.SS Linux libc
In the early to mid 1990s, there was for a while
.IR "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, 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 over a decade ago,
.I 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
.IR libc4
and
.IR libc5 .)
.SS Other C libraries
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
.I uClibc
.RI ( http://www.uclibc.org/ )
and
.I dietlibc
.RI ( http://www.fefe.de/dietlibc/ ).
Details of these libraries are generally not covered by the
.I man-pages
project.
.SH SEE ALSO
.BR syscalls (2),
.BR feature_test_macros (7),
.BR man-pages (7),
.BR standards (7)
Commit	Line	Data
383354a9 MK	1	.\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
	2	.\" <mtk.manpages@gmail.com>
	3	.\"
4b72fb64	4	.\" %%%LICENSE_START(verbatim)
383354a9 MK	5	.\" Permission is granted to make and distribute verbatim copies of this
	6	.\" manual provided the copyright notice and this permission notice are
	7	.\" preserved on all copies.
	8	.\"
	9	.\" Permission is granted to copy and distribute modified versions of this
	10	.\" manual under the conditions for verbatim copying, provided that the
	11	.\" entire resulting derived work is distributed under the terms of a
	12	.\" permission notice identical to this one.
	13	.\"
	14	.\" Since the Linux kernel and libraries are constantly changing, this
	15	.\" manual page may be incorrect or out-of-date. The author(s) assume no
	16	.\" responsibility for errors or omissions, or for damages resulting from
	17	.\" the use of the information contained herein. The author(s) may not
	18	.\" have taken the same level of care in the production of this manual,
	19	.\" which is licensed free of charge, as they might when working
	20	.\" professionally.
	21	.\"
	22	.\" Formatted or processed versions of this manual, if unaccompanied by
	23	.\" the source, must acknowledge the copyright and authors of this work.
4b72fb64	24	.\" %%%LICENSE_END
383354a9	25	.\"
608bf950	26	.TH LIBC 7 2012-08-05 "Linux" "Linux Programmer's Manual"
383354a9	27	.SH NAME
f68512e9	28	libc \- overview of standard C libraries on Linux
383354a9 MK	29	.SH DESCRIPTION
	30	The term "libc" is commonly used as a shorthand for
	31	the "standard C library",
	32	a library of standard functions that can be used by all C programs
	33	(and sometimes by programs in other languages).
	34	Because of some history (see below), use of the term "libc"
	35	to refer to the standard C library is somewhat ambiguous on Linux.
	36	.SS glibc
	37	By far the most widely used C library on Linux is the GNU C Library
608bf950 SK	38	.UR http://www.gnu.org\:/software\:/libc/
608bf950 SK	39	.UE ,
383354a9 MK	40	often referred to as
	41	.IR glibc .
	42	This is the C library that is nowadays used in all
	43	major Linux distributions.
	44	It is also the C library whose details are documented
	45	in the relevant pages of the
	46	.I man-pages
	47	project (primarily in Section 3 of the manual).
	48	Documentation of glibc is also available in the glibc manual,
	49	available via the command
	50	.IR "info libc" .
	51	Release 1.0 of glibc was made in September 1992.
	52	(There were earlier 0.x releases.)
	53	The next major release of glibc was 2.0, at the beginning of 1997.
	54
	55	The pathname
	56	.I /lib/libc.so.6
	57	(or something similar) is normally a symbolic link that
	58	points to the location of the glibc library,
	59	and executing this pathname will cause glibc to display
	60	various information about the version installed on your system.
	61	.SS Linux libc
	62	In the early to mid 1990s, there was for a while
	63	.IR "Linux libc" ,
	64	a fork of glibc 1.x created by Linux developers who felt that glibc
	65	development at the time was not sufficing for the needs of Linux.
	66	Often, this library was referred to (ambiguously) as just "libc".
	67	Linux libc released major versions 2, 3, 4, and 5
	68	(as well as many minor versions of those releases).
	69	For a while,
	70	Linux libc was the standard C library in many Linux distributions.
	71	However, notwithstanding the original motivations of the Linux libc effort,
	72	by the time glibc 2.0 was released, it was clearly superior to Linux libc,
	73	and all major Linux distributions that had been using Linux libc
	74	soon switched back to glibc.
	75	(Since this switch occurred over a decade ago,
	76	.I man-pages
	77	no longer takes care to document Linux libc details.
	78	Nevertheless, the history is visible in vestiges of information
	79	about Linux libc that remain in some manual pages,
	80	in particular, references to
	81	.IR libc4
	82	and
	83	.IR libc5 .)
	84	.SS Other C libraries
	85	There are various other less widely used C libraries for Linux.
	86	These libraries are generally smaller than glibc,
	87	both in terms of features and memory footprint,
	88	and often intended for building small binaries,
	89	perhaps targeted at development for embedded Linux systems.
	90	Among such libraries are
	91	.I uClibc
	92	.RI ( http://www.uclibc.org/ )
	93	and
	94	.I dietlibc
d6dcce39	95	.RI ( http://www.fefe.de/dietlibc/ ).
383354a9 MK	96	Details of these libraries are generally not covered by the
	97	.I man-pages
	98	project.
	99	.SH SEE ALSO
383354a9 MK	100	.BR syscalls (2),
	101	.BR feature_test_macros (7),
	102	.BR man-pages (7),
	103	.BR standards (7)