LIBC(7)                   (2016-12-12)                    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 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 Sec-
          tion 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 nor-
          mally 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 (prim-
          itive) 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.

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          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 dietlibc and musl libc 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/.

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