libc(7) - man - phpMan

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



NAME
       libc - overview of standard C libraries on Linux

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.

   glibc
       By far the most widely used C library on Linux  is  the  GNU  C  Library  ⟨http://www.gnu.org
       /software/libc/⟩, often referred to as 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 man-pages project (primarily in Section 3 of the manual).  Documenta‐
       tion of glibc is also available in the glibc manual, available via  the  command  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 /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.

   Linux libc
       In the early to mid 1990s, there was for a while 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  re‐
       leased  major  versions  2,  3,  4,  and 5, as well as many minor versions of those releases.
       Linux libc4 was the last version to use the a.out binary format, and  the  first  version  to
       provide  (primitive)  shared  library support.  Linux libc 5 was the first version to support
       the ELF binary format; this version used the shared library soname libc.so.5.  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 (in 1997), it was clearly superior to Linux libc, and all major  Linux  dis‐
       tributions  that  had been using Linux libc soon switched back to glibc.  To avoid any confu‐
       sion with Linux libc versions, glibc 2.0 and later used the shared library soname libc.so.6.

       Since the switch from Linux libc to glibc 2.0 occurred long ago, man-pages  no  longer  takes
       care to document Linux libc details.  Nevertheless, the history is visible in vestiges of in‐
       formation about Linux libc that remain in a few manual pages, in  particular,  references  to
       libc4 and libc5.

   Other C libraries
       There  are  various other less widely used C libraries for Linux.  These libraries are gener‐
       ally 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      uClibc      ⟨http://www.uclibc.org/⟩,      dietlibc
       ⟨http://www.fefe.de/dietlibc/⟩,  and musl libc ⟨http://www.musl-libc.org/⟩.  Details of these
       libraries are covered by the man-pages project, where they are known.

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

COLOPHON
       This  page  is  part  of  release  5.10 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of this page, can be  found
       at https://www.kernel.org/doc/man-pages/.



Linux                                        2016-12-12                                      LIBC(7)