1 man
2 info
3 apropos
4 whatis
5 makewhatis
[edit] man
man displays the manual page for the specified command
A useful option is:
-k TEXT search manual page titles and synopsis lines for TEXT
Examples:
To display the manual page for the chown command:
$ man chown
man has different sections.
section 1 is user commands
section 2 is system calls (used by programs to communicate
with the kernel)
section 3 is library reference (for programming in C)
section 4 is device drivers
section 5 is configuration files and other file formats
section 6 is games
section 7 is miscellaneous (for example, "ascii" map
and C "operator" precedence)
section 8 is system commands (like user commands, but
mostly for root)
A section number can be specified before the page name. For example, man chmod normally shows the user command "chmod". To see the system call "chmod":
$ man 2 chmod
To search the man pages for "newsgroups",
$ man -k newsgroups
actsync
(8) - synchronize newsgroupsoups
newsgroups
(1) - a program to list unsubscribed newsgroups
If this does not work you may have to run the makewhatis command.
[edit] info
info is an advanced man command that is sometimes available.
It displays the improved manual pages in Info format for specified command.
Examples:
To display the manual page for the grep command:
$ info grep
To find occurrence of 'grep' in all info manual pages:
$ info --apropos grep
"(autoconf-2.13)Examining Declarations" -- EGREP_CPP
"(autoconf-2.13)Examining Declarations" -- EGREP_HEADER
"(autoconf-2.13)Old Macro Names" -- HEADER_EGREP
...
Some copies of info lack the "-w" option.
To see the physical location of 'grep' info manual page:
$ info -w grep
/usr/share/info/grep.info.gz
To view a file a info page:
$ info -f ./some_cmd.info.gz
[edit] apropos
apropos searches the manual page short descriptions for a specified keyword
On many systems this is exactly the same as the -k option of the man command.
Examples:
$ apropos newsgroups
active
(5) - list of active Usenet newsgroups
newsgroups
(1) - a program to list unsubscribed newsgroups
[edit] whatis
whatis displays short man page descriptions. Unlike
Examples:
$ whatis info
info (1)
- read Info documents
info (5)
- readable online documentation
$ whatis chmod
chmod (1) - change file modes
chmod, fchmod (2) - change mode of file
[edit] makewhatis
makewhatis creates the database for the whatis, appropos, and man -k commands. This is commonly run automatically by your system however sometimes you need to run this manually.
Examples:
# makewhatis
$ sudo makewhatis
