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/">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 http://www.uclibc.org/">uClibc,
http://www.fefe.de/dietlibc/">dietlibc,
and http://www.musl-libc.org/">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 5.09 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/.