LIBC(7) Linux Programmer's Manual LIBC(7)
libc - overview of standard C libraries on Linux
The term "libc" is commonly used as a shorthand for the "standard C li-
brary", a library of standard functions that can be used by all C pro-
grams (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.
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 distribu-
tions. 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 re-
lease of glibc was 2.0, at the beginning of 1997.
The pathname /lib/libc.so.6 (or something similar) is normally a sym-
bolic 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.
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 li-
brary was referred to (ambiguously) as just "libc". Linux libc re-
leased 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 bi-
nary format, and the first version to provide (primitive) shared li-
brary 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 dis-
However, notwithstanding the original motivations of the Linux libc ef-
fort, by the time glibc 2.0 was released (in 1997), it was clearly su-
perior 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
Since the switch from Linux libc to glibc 2.0 occurred long ago, man-
pages no longer takes care to document Linux libc details. Neverthe-
less, 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.
syscalls(2), getauxval(3), proc(5), feature_test_macros(7), man-
pages(7), standards(7), vdso(7)
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latest version of this page, can be found at
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