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1 .\" Copyright (c) 2009 Linux Foundation, written by Michael Kerrisk
2 .\" <mtk.manpages@gmail.com>
3 .\"
4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
5 .\"
6 .TH libc 7 (date) "Linux man-pages (unreleased)"
7 .SH NAME
8 libc \- overview of standard C libraries on Linux
9 .SH DESCRIPTION
10 The term \[lq]libc\[rq] is commonly used as a shorthand for
11 the \[lq]standard C library\[rq]
12 a library of standard functions that can be used by all C programs
13 (and sometimes by programs in other languages).
14 Because of some history
15 (see below),
16 use of the term \[lq]libc\[rq]
17 to refer to the standard C library is somewhat ambiguous on Linux.
18 .SS glibc
19 By far the most widely used C library on Linux is the
20 .UR http://www.gnu.org\:/software\:/libc/
21 GNU C Library
22 .UE ,
23 often referred to as
24 .IR glibc .
25 This is the C library that is nowadays used in all
26 major Linux distributions.
27 It is also the C library whose details are documented
28 in the relevant pages of the
29 .I man-pages
30 project
31 (primarily in Section 3 of the manual).
32 Documentation of glibc is also available in the glibc manual,
33 available via the command
34 .IR "info libc" .
35 Release 1.0 of glibc was made in September 1992.
36 (There were earlier 0.x releases.)
37 The next major release of glibc was 2.0,
38 at the beginning of 1997.
39 .P
40 The pathname
41 .I /lib/libc.so.6
42 (or something similar)
43 is normally a symbolic link that
44 points to the location of the glibc library,
45 and executing this pathname will cause glibc to display
46 various information about the version installed on your system.
47 .SS Linux libc
48 In the early to mid 1990s,
49 there was for a while
50 .IR "Linux libc" ,
51 a fork of glibc 1.x created by Linux developers who felt that glibc
52 development at the time was not sufficing for the needs of Linux.
53 Often,
54 this library was referred to (ambiguously) as just \[lq]libc\[rq].
55 Linux libc released major versions 2, 3, 4, and 5,
56 as well as many minor versions of those releases.
57 Linux libc4 was the last version to use the a.out binary format,
58 and the first version to provide (primitive) shared library support.
59 Linux libc 5 was the first version to support the ELF binary format;
60 this version used the shared library soname
61 .IR libc.so.5 .
62 For a while,
63 Linux libc was the standard C library in many Linux distributions.
64 .P
65 However,
66 notwithstanding the original motivations of the Linux libc effort,
67 by the time glibc 2.0 was released
68 (in 1997),
69 it was clearly superior to Linux libc,
70 and all major Linux distributions that had been using Linux libc
71 soon switched back to glibc.
72 To avoid any confusion with Linux libc versions,
73 glibc 2.0 and later used the shared library soname
74 .IR libc.so.6 .
75 .P
76 Since the switch from Linux libc to glibc 2.0 occurred long ago,
77 .I man-pages
78 no longer takes care to document Linux libc details.
79 Nevertheless,
80 the history is visible in vestiges of information
81 about Linux libc that remain in a few manual pages,
82 in particular,
83 references to
84 .I libc4
85 and
86 .IR libc5 .
87 .SS Other C libraries
88 There are various other less widely used C libraries for Linux.
89 These libraries are generally smaller than glibc,
90 both in terms of features and memory footprint,
91 and often intended for building small binaries,
92 perhaps targeted at development for embedded Linux systems.
93 Among such libraries are
94 .UR http://www\:.uclibc\:.org/
95 .I uClibc
96 .UE ,
97 .UR http://www\:.fefe\:.de/\:dietlibc/
98 .I dietlibc
99 .UE ,
100 and
101 .UR http://www\:.musl\-libc\:.org/
102 .I "musl libc"
103 .UE .
104 Details of these libraries are covered by the
105 .I man-pages
106 project,
107 where they are known.
108 .SH SEE ALSO
109 .BR syscalls (2),
110 .BR getauxval (3),
111 .BR proc (5),
112 .BR feature_test_macros (7),
113 .BR man\-pages (7),
114 .BR standards (7),
115 .BR vdso (7)