Guide to Unix/Commands/Getting Help
man displays the manual page for the specified command
A useful option is:
$ man -k TEXT
This searches manual page titles and synopsis lines for TEXT
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.
info is an advanced man command that is sometimes available. It displays the improved manual pages in Info format for specified command.
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
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.
$ apropos newsgroups active (5) - list of active Usenet newsgroups newsgroups (1) - a program to list unsubscribed newsgroups
whatis displays short man page descriptions. Unlike
$ 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
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.
$ sudo makewhatis