man > libc(7)

libc(7)                           Miscellaneous Information 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 ]8;;http://www.gnu.org/software/libc/\GNU C Library]8;;\,  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).  Documentation of glibc is also available in
       the glibc manual, available via the command info libc.  Release 1.0 of glibc was made in Sep‐
       tember 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  ]8;;http://www.uclibc.org/\uClibc]8;;\, ]8;;http://www.fefe.de/dietlibc/\dietlibc]8;;\, and ]8;;http://www.musl-libc.org/\musl libc]8;;\.  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)

Linux man-pages 6.7                          2023-10-31                                      libc(7)