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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
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 re-
leases.) 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 dis-
play 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 re-
leases. 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 gen-
erally smaller than glibc, both in terms of features and memory footprint, and often in-
tended 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 5.10 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/.
Linux 2016-12-12 LIBC(7)
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