libc(7) Miscellaneous Information 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 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.
glibc
By far the most widely used C library on Linux is the ]8;;http://www.gnu.org/software/libc/\GNU C Library]8;;\, of-
ten 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 de-
tails 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. Re-
lease 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 sym-
bolic link that points to the location of the glibc library, and execut-
ing 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 re-
leases. Linux libc4 was the last version to use the a.out binary for-
mat, and the first version to provide (primitive) shared library sup-
port. Linux libc 5 was the first version to support the ELF binary for-
mat; this version used the shared library soname libc.so.5. For a
while, Linux libc was the standard C library in many Linux distribu-
tions.
However, notwithstanding the original motivations of the Linux libc ef-
fort, by the time glibc 2.0 was released (in 1997), it was clearly supe-
rior to Linux libc, and all major Linux distributions that had been us-
ing 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. 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 ]8;;http://www.uclibc.org/\uClibc]8;;\, ]8;;http://www.fefe.de/dietlibc/\dietlibc]8;;\, and ]8;;http://www.musl-libc.org/\musl libc]8;;\. Details of these li-
braries 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)
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