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libc(7) [debian man page]

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 stan-
       dard 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 rel-
       evant 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 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  develop-
       ment  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).  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, it was clearly superior to Linux libc, and all major Linux distributions that had been using Linux libc  soon	switched  back	to
       glibc.	(Since	this  switch occurred over a decade 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 some 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 fea-
       tures 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/) and dietlibc (http://www.fefe.de/dietlibc/).  Details of these libraries are gen-
       erally not covered by the man-pages project.

SEE ALSO

       syscalls(2), feature_test_macros(7), man-pages(7), standards(7)

COLOPHON

       This page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2012-08-05								   LIBC(7)

Check Out this Related Man Page

USELIB(2)						     Linux Programmer's Manual							 USELIB(2)

NAME

       uselib - load shared library

SYNOPSIS

       #include <unistd.h>

       int uselib(const char *library);

       Note: No declaration of this system call is provided in glibc headers; see NOTES.

DESCRIPTION

       The  system call uselib() serves to load a shared library to be used by the calling process.  It is given a pathname.  The address where to
       load is found in the library itself.  The library can have any recognized binary format.

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS

       In addition to all of the error codes returned by open(2) and mmap(2), the following may also be returned:

       EACCES The library specified by library does not have read or execute permission, or the caller does not have search permission for one	of
	      the directories in the path prefix.  (See also path_resolution(7).)

       ENFILE The system-wide limit on the total number of open files has been reached.

       ENOEXEC
	      The file specified by library is not an executable of a known type; for example, it does not have the correct magic numbers.

CONFORMING TO

       uselib() is Linux-specific, and should not be used in programs intended to be portable.

NOTES

       This  obsolete  system call is not supported by glibc.  No declaration is provided in glibc headers, but, through a quirk of history, glibc
       versions before 2.23 did export an ABI for this system call.  Therefore, in order to employ this system call, it was sufficient to manually
       declare the interface in your code; alternatively, you could invoke the system call using syscall(2).

       In ancient libc versions, uselib() was used to load the shared libraries with names found in an array of names in the binary.

       Since  libc 4.3.2, startup code tries to prefix these names with "/usr/lib", "/lib" and "" before giving up.  In libc 4.3.4 and later these
       names are looked for in the directories found in LD_LIBRARY_PATH, and if not found there, prefixes "/usr/lib", "/lib" and "/" are tried.

       From libc 4.4.4 on only the library "/lib/ld.so" is loaded, so that this dynamic library can load the  remaining  libraries  needed  (again
       using this call).  This is also the state of affairs in libc5.

       glibc2 does not use this call.

       Since Linux 3.15, this system call is available only when the kernel is configured with the CONFIG_USELIB option.

SEE ALSO

       ar(1), gcc(1), ld(1), ldd(1), mmap(2), open(2), dlopen(3), capabilities(7), ld.so(8)

COLOPHON

       This  page is part of release 4.15 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								    2017-09-15								 USELIB(2)
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