libc

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 li-
       brary", a library of standard functions that can be used by all C  pro-
       grams  (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 distribu-
       tions.  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
       September 1992.  (There were earlier 0.x releases.)  The next major re-
       lease of glibc was 2.0, at the beginning of 1997.

       The  pathname  /lib/libc.so.6 (or something similar) is normally a sym-
       bolic link that points to the location of the glibc library,  and  exe-
       cuting  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  li-
       brary  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 bi-
       nary format, and the first version to provide  (primitive)  shared  li-
       brary  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 dis-
       tributions.

       However, notwithstanding the original motivations of the Linux libc ef-
       fort,  by the time glibc 2.0 was released (in 1997), it was clearly su-
       perior to Linux libc, and all major Linux distributions that  had  been
       using  Linux  libc soon switched back to glibc.  To avoid any confusion
       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.   Neverthe-
       less,  the  history  is  visible in vestiges of information 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 generally 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 5.05 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)