On Unix, the main form of on-line documentation was the manual page or man page. In the GNU operating system, we aim to replace man pages with better-organized manuals that you can browse with Info (see Misc Help). This process is not finished, so it is still useful to read manual pages.
You can read the man page for an operating system command, library function, or system call, with the M-x man command. This prompts for a topic, with completion (see Completion), and runs the man program to format the corresponding man page. If the system permits, it runs man asynchronously, so that you can keep on editing while the page is being formatted. The result goes in a buffer named *Man topic*. These buffers use a special major mode, Man mode, that facilitates scrolling and jumping to other manual pages. For details, type C-h m while in a Man mode buffer.
Each man page belongs to one of ten or more sections, each
named by a digit or by a digit and a letter. Sometimes there are man
pages with the same name in different sections. To read a man page
from a specific section, type ‘topic(section)’ or
‘section topic’ when M-x manual-entry prompts
for the topic. For example, the man page for the C library function
chmod is in section 2, but there is a shell command of the same
name, whose man page is in section 1; to view the former, type
M-x manual-entry <RET> chmod(2) <RET>.
If you do not specify a section, M-x man normally displays
only the first man page found. On some systems, the
program accepts a ‘-a’ command-line option, which tells it to
display all the man pages for the specified topic. To make use of
this, change the value of the variable
‘"-a"’. Then, in the Man mode buffer, you can type M-n and
M-p to switch between man pages in different sections. The mode
line shows how many manual pages are available.
An alternative way of reading manual pages is the M-x woman command. Unlike M-x man, it does not run any external programs to format and display the man pages; the formatting is done by Emacs, so it works on systems such as MS-Windows where the man program may be unavailable. It prompts for a man page, and displays it in a buffer named *WoMan section topic.
M-x woman computes the completion list for manpages the first time you invoke the command. With a numeric argument, it recomputes this list; this is useful if you add or delete manual pages.
If you type a name of a manual page and M-x woman finds that several manual pages by the same name exist in different sections, it pops up a window with possible candidates asking you to choose one of them.
For more information about setting up and using M-x woman, see the WoMan Info manual, which is distributed with Emacs.