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).  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 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
   released 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 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.
   Nevertheless,  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 4.09 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/.

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