1libc(7) Miscellaneous Information Manual libc(7)
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6 libc - overview of standard C libraries on Linux
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9 The term “libc” is commonly used as a shorthand for the “standard C li‐
10 brary” a library of standard functions that can be used by all C pro‐
11 grams (and sometimes by programs in other languages). Because of some
12 history (see below), use of the term “libc” to refer to the standard C
13 library is somewhat ambiguous on Linux.
14 glibc
16 By far the most widely used C library on Linux is the GNU C Library
17 ⟨http://www.gnu.org/software/libc/⟩, often referred to as glibc. This
18 is the C library that is nowadays used in all major Linux distribu‐
19 tions. It is also the C library whose details are documented in the
20 relevant pages of the man-pages project (primarily in Section 3 of the
21 manual). Documentation of glibc is also available in the glibc manual,
22 available via the command info libc. Release 1.0 of glibc was made in
23 September 1992. (There were earlier 0.x releases.) The next major re‐
24 lease of glibc was 2.0, at the beginning of 1997.
25 The pathname /lib/libc.so.6 (or something similar) is normally a sym‐
27 bolic link that points to the location of the glibc library, and exe‐
28 cuting this pathname will cause glibc to display various information
29 about the version installed on your system.
30 Linux libc
32 In the early to mid 1990s, there was for a while Linux libc, a fork of
33 glibc 1.x created by Linux developers who felt that glibc development
34 at the time was not sufficing for the needs of Linux. Often, this li‐
35 brary was referred to (ambiguously) as just “libc”. Linux libc re‐
36 leased major versions 2, 3, 4, and 5, as well as many minor versions of
37 those releases. Linux libc4 was the last version to use the a.out bi‐
38 nary format, and the first version to provide (primitive) shared li‐
39 brary support. Linux libc 5 was the first version to support the ELF
40 binary format; this version used the shared library soname libc.so.5.
41 For a while, Linux libc was the standard C library in many Linux dis‐
42 tributions.
43 However, notwithstanding the original motivations of the Linux libc ef‐
45 fort, by the time glibc 2.0 was released (in 1997), it was clearly su‐
46 perior to Linux libc, and all major Linux distributions that had been
47 using Linux libc soon switched back to glibc. To avoid any confusion
48 with Linux libc versions, glibc 2.0 and later used the shared library
49 soname libc.so.6.
50 Since the switch from Linux libc to glibc 2.0 occurred long ago, man-
52 pages no longer takes care to document Linux libc details. Neverthe‐
53 less, the history is visible in vestiges of information about Linux
54 libc that remain in a few manual pages, in particular, references to
55 libc4 and libc5.
56 Other C libraries
58 There are various other less widely used C libraries for Linux. These
59 libraries are generally smaller than glibc, both in terms of features
60 and memory footprint, and often intended for building small binaries,
61 perhaps targeted at development for embedded Linux systems. Among such
62 libraries are uClibc ⟨http://www.uclibc.org/⟩, dietlibc ⟨http://www
63 .fefe.de/dietlibc/⟩, and musl libc ⟨http://www.musl-libc.org/⟩. De‐
64 tails of these libraries are covered by the man-pages project, where
65 they are known.
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68 syscalls(2), getauxval(3), proc(5), feature_test_macros(7),
69 man-pages(7), standards(7), vdso(7)
70Linux man-pages 6.05 2023-02-05 libc(7)