Content: * Define the term "standard C library". * Say who's responsible for standardizing it. * Move material describing structure glibc from intro(3) to here and recast in more detail. * Update example filespec for libc.so.6. Style: * Set `TH` page title in lowercase, since the migration is underway. * Say "GNU/Linux distributions" instead of "Linux distributions". * Tighten wording. Markup: * Use typographer's quotation marks instead of '"' for quotation. * Hyperlink "the GNU C Library" correctly. * Use `P` instead of `PP` paragraphing macro. * Add hyphenation breaks to URLs and the new unwieldy ISO WG identifier. --- man7/libc.7 | 157 ++++++++++++++++++++++++++++++++-------------------- 1 file changed, 98 insertions(+), 59 deletions(-) diff --git a/man7/libc.7 b/man7/libc.7 index 12c79dc11..f5cda54ef 100644 --- a/man7/libc.7 +++ b/man7/libc.7 @@ -3,95 +3,134 @@ .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" -.TH LIBC 7 (date) "Linux man-pages (unreleased)" +.TH libc 7 (date) "Linux man-pages (unreleased)" .SH NAME libc \- overview of standard C libraries on Linux .SH 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. +The term \(lqlibc\(rq is commonly used as a shorthand for +the +.IR "standard C library" , +a collection of functions, +data types, +constants, +and global variables \" like errno +defined by ISO/IEC JTC1/\:SC22/\:WG14 and POSIX.1 +(the Austin Group) +and used by practically all programs written in C. +.I libc +refers to any library that implements a significant portion of the +published standard interface. .SS glibc -By far the most widely used C library on Linux is the GNU C Library +The standard libc most popularly used with the Linux kernel is .UR http://www.gnu.org\:/software\:/libc/ +the GNU C Library .UE , -often referred to as +widely called .IR 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 +This implementation is nowadays used +in all major GNU/Linux distributions. +Its details are documented in the relevant pages of the +Linux .I man-pages -project (primarily in Section 3 of the manual). -Documentation of glibc is also available in the glibc manual, -available via the command -.IR "info libc" . -Release 1.0 of glibc was made in September 1992. +project, +primarily in section 3 of the manual. +glibc also offers a manual of its own in Texinfo format, +browsable at the command line with +.RI \(lq "info libc" \(rq. +.P +glibc is organized into three +.I dynamic shared objects +(DSOs): +.I libc +itself, +.I libm +for mathematical functions, +and +.I librt +for real-time extensions +(historically POSIX.1b). +.P +Version 1.0 of glibc was released in September 1992. (There were earlier 0.x releases.) -The next major release of glibc was 2.0, at the beginning of 1997. -.PP -The pathname -.I /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. +The next major release of glibc was 2.0 +at the beginning of 1997. +.P +The file +.IR /lib/libc.so.6 , +.IR /lib/x86_64\-linux\-gnu/libc.so.6 , +or similar +is normally a symbolic link to the glibc library. +Execute it to display information about the version installed on your +system. .SS Linux libc -In the early to mid 1990s, there was for a while +In the early to mid-1990s, .IR "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". +a fork of glibc\~1, +was maintained by Linux developers +who felt that glibc development at the time +did not meet the Linux user community's needs. +Often, +this library was referred to, +simply and ambiguously, +as \(lqlibc\(rq. 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 +along with many minor updates. +Linux libc\~4 was the last to use the +object file format called \(lqa.out\(rq, +and the first on Linux to provide (primitive) shared library support. +Linux libc\~5 was the first on Linux to support ELF object code; +it employed the +.I soname +(shared object name) .IR libc.so.5 . For a while, -Linux libc was the standard C library in many Linux distributions. -.PP -However, notwithstanding the original motivations of the Linux libc effort, -by the time glibc 2.0 was released (in 1997), +Linux libc was the standard C library in many GNU/Linux distributions. +.P +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. -To avoid any confusion with Linux libc versions, -glibc 2.0 and later used the shared library soname -.IR libc.so.6 . -.PP +and all major distributions that had been using Linux libc +soon switched (back) to glibc. +To avoid confusion with Linux libc versioning, +glibc 2.0 and later use the soname +.I libc.so.6 +on Linux systems to indicate their status as successors +to Linux libc\~5. +.P Since the switch from Linux libc to glibc 2.0 occurred long ago, .I 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 +Nevertheless, +vestiges of this history linger in comments +about Linux libc in a few manual pages\(em\ +in particular, +references to .I libc4 and .IR libc5 . .SS 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. +Other, +less widely used, +C libraries for Linux exist. +They are generally smaller than glibc +in terms of features and memory footprint, +and are often intended for building small binaries, +such as those targetting embedded systems. Among such libraries are -.UR http://www.uclibc.org/ +.UR http://www\:.uclibc\:.org/ .I uClibc .UE , -.UR http://www.fefe.de/dietlibc/ -.I dietlibc +.UR http://www\:.fefe\:.de/\:dietlibc/ +.I \%diet\%libc .UE , and -.UR http://www.musl\-libc.org/ -.I "musl libc" +.UR http://www\:.musl\-libc\:.org/ +.I musl libc .UE . -Details of these libraries are covered by the +Details of these are offered by .I man-pages -project, where they are known. +where known. .SH SEE ALSO .BR syscalls (2), .BR getauxval (3), -- 2.30.2
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