1LIBC(7)                    Linux Programmer's Manual                   LIBC(7)


6       libc - overview of standard C libraries on Linux


9       The  term  "libc"  is  commonly used as a shorthand for the "standard C
10       library", a library of standard functions that can be  used  by  all  C
11       programs  (and  sometimes  by programs in other languages).  Because of
12       some history (see below), use of the term "libc" to refer to the  stan‐
13       dard C library is somewhat ambiguous on Linux.
15   glibc
16       By  far  the  most  widely used C library on Linux is the GNU C Library
17http://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
24       release of glibc was 2.0, at the beginning of 1997.
26       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.
31   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
35       library  was  referred  to  (ambiguously)  as  just "libc".  Linux libc
36       released major versions 2, 3, 4, and 5, as well as many minor  versions
37       of  those  releases.  Linux libc4 was the last version to use the a.out
38       binary format, and the first  version  to  provide  (primitive)  shared
39       library 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.
44       However, notwithstanding the original motivations  of  the  Linux  libc
45       effort,  by  the  time glibc 2.0 was released (in 1997), it was clearly
46       superior 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.
51       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.
57   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     uClibchttp://www.uclibc.org/⟩,     dietlibc
63http://www.fefe.de/dietlibc/⟩,         and          musl          libc
64http://www.musl-libc.org/⟩.  Details of these libraries are covered by
65       the man-pages project, where they are known.


68       syscalls(2),  getauxval(3),   proc(5),   feature_test_macros(7),   man-
69       pages(7), standards(7), vdso(7)


72       This  page  is  part of release 4.16 of the Linux man-pages project.  A
73       description of the project, information about reporting bugs,  and  the
74       latest     version     of     this    page,    can    be    found    at
75       https://www.kernel.org/doc/man-pages/.
79Linux                             2016-12-12                           LIBC(7)