Most popular manual format and reader.
POSIX 7: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/man.html
man man
The main format read by man is troff, which has a GNU implementation called groff. It comes from Unix AT&T days. troff is human readable.
The usual extension for troff are digits from 1 to 8 which represent the page it belongs to.
Open a given troff file:
man ./gcc.1
The ./ is mandatory: if there are no slashes on the argument, man searches in a search path, which is the most common use case.
POSIX 7 specifies only the option -k and nothing about pages, those are Linux concepts.
The manual is organized into 7 pages.
When you install a new page, the developers decide where to put the documentation.
Every page has an intro section which says what it is about:
man 2 intro
man 3 intro
As in the case of the intro, you can distinguish ambiguities by giving the page number.
write system call:
man 2 write
write shell command:
man 1 write
List all entries of a page:
man -k . | grep '(8)'
User commands (executables in path).
This is normally the largest section.
man 1 passwd
System calls: C interface.
Those are not actual system calls, but portable low level system interfaces, many of which directly wrap a system call.
Most of the POSIX C library is here.
POSIX write function:
man 2 write
Library C functions.
Higher level functions than section 2.
Contains for example:
- some POSIX APIs like
pthreadis - X11 APIs
Special files such as device files:
man 4 zero
man 4 random
man 4 mouse
File formats specifications.
Examples:
/etc/passwd file syntax:
man 5 passwd
ELF executable format:
man 5 elf
Games.
Standards.
Contains standards summaries such as:
man unicode
man url
man X
System administration
Commands that mostly only root can do.
Their binaries are typically under /usr/sbin/.
Examples:
man 8 adduser
man 8 grub-install
man 8 mount
Kernel routines. Linux extension. Generated with make mandocs on the kernel.
Exact search on title. Shows only first page found match:
man intro
Show each match in succession and asks if you want to continue to the next on each quit:
man -a intro
Without that option, shows only one page then quits.
Summary:
man -k password
Entire text:
man -K password
May be slow:
Whatever you were searching search with ERE now.
Regex on title:
man --regex 'a.c'
Regex on entire manual:
man --regex -K 'a.c'
Same
apropos password
List all manual pages pages whose summaries match '.' regex: (any character):
man -k .
https://www.kernel.org/doc/man-pages/
Project that maintains many Linux related manpages and also some non Linux specific entries.
Most distros to come with those manpages installed.
It is not a part of the kernel tree, and does not seem to be mentioned in the LSB.
Show man short description of ls.
whatis ls
Get the man search path:
manpath
Sample output:
#/usr/local/man:/usr/local/share/man:/usr/share/man
Languages man:
ls /usr/share/man
Section 1 pages in English:
ls /usr/share/man/man1 | less
There is one single and drastic advantage to it: clickable references to other manpages
Ubuntu default documentation front-end. Also does other formats.
yelp man:ls