Usage
The UNIX Programmer's Manual was first published on November 3, 1971. However, online man pages were not available until the release of the 7th Edition in 1979. At the time, the availability of online documentation through the manual page system was regarded as a great advance. To this day, virtually every Unix command line application comes with its man page, and many Unix users perceive a lack of man pages as a sign of low quality; indeed, some projects, such as Debian, go out of their way to write man pages for programs lacking one. Few alternatives to man have enjoyed much popularity, with the possible exception of the GNU project's "info" system, an early and simple hypertext system.
However, the format of a single page for each application, the lack of classification within the sections and the relatively unsophisticated formatting facilities have motivated the development of alternative documentation systems, such as the previously mentioned info system.
Most Unix GUI applications (particularly those built using the GNOME and KDE development environments) now provide end-user documentation in HTML and include embedded HTML viewers for reading the help within the application.
Usually the man pages are written in English. Translations into other languages can be also available on the system.
The default format of the man pages is troff, with either the macro package man (appearance oriented) or mdoc (semantic oriented). This makes it possible to typeset a man page to PostScript, PDF and various other formats for viewing or printing (although most users still prefer the default terminal interface).

History
The manual is generally split into eight numbered sections, organized as follows (on BSD Unix and Linux):
Unix System V uses a similar numbering scheme, except section 4 is file formats, section 5 is miscellany and section 7 is special files.
On some systems some of the following sections are available:
The sections are further subdivided by means of a suffix letter, such that section 3C is for C library calls, 3M is for the math library, and so on. A consequence of this is that section 8 (system administration commands) is sometimes relegated to the 1M subsection of the main commands section. Some subsection suffixes have a general meaning across sections:
The manual pages are stored as nroff source files. Most versions of man cache the formatted versions of the last several pages viewed.
To see options you can use with command man, enter the command man man.

Layout

List of Unix programs
List of Plan 9 applications
Info (Unix)
RTFM