The man command is used to format and display the man pages. The man pages are a user manual that is by default built into most Linux distributions (i.e., versions) and most other Unix-like operating systems during installation. They provide extensive documentation about commands and other aspects of the system, including configuration files, system calls, library routines and the kernel (i.e., the core of the operating system). A configuration file is a type of simple database that contains data that tells a program or operating system how to behave. A system call is a request made via a software interrupt (i.e., a signal to the kernel initiated by software) by an active process for a service performed by the kernel. A library routine is a subprogram that is used by programmers to simplify the development of software. The man pages are tailored to the particular operating system, and version thereof, on which they are installed. This is beneficial because there can be slight differences in commands and other items according to the particular system. The descriptions are rather terse, and they can seem somewhat cryptic to new users. However, users typically find them to be increasingly useful as they become more familiar with them and gain experience in the use of Unix-like operating systems. The man command itself is extremely easy to use. Its basic syntax is
man is most commonly used without any options and with only one keyword. The keyword is the exact name of the command or other item for which information is desired. For example, the following provides information about the ls command (which is used to list the contents of any specified directory):
As another example, the following displays the man page about the man pages:
man automatically sends its output through a pager, usually the program less. A pager is a program that causes the output of any program to be displayed one screenful at a time, rather than having a large amount of text scroll down the screen at high (and generally unreadable) speed. less writes a colon at the bottom of the screen to indicate the end of the on-screen page. The user can move to the next page by pushing the space bar and can return to the previous page by pressing the b key. Pressing the q exits the man pages and returns the user to the shell program. Each man page is a self-contained article that is divided into a number of sections, the headers for which are labeled with upper case letters. The sections for commands are typically something like NAME, SYNOPSIS, DESCRIPTION, OPTIONS, AUTHOR, BUGS, COPYRIGHT, HISTORY and SEE ALSO, although there may be some differences according to the particular command. Some of these might be broken down into subsections, particularly OPTIONS in the case of a command that has numerous options. Also, the man pages as a whole are organized into sections, each containing pages about a specific category of topics as shown below. The section to which an article belongs is indicted in parenthesis in the top line, before the NAME header. 1. executable programs or shell commands Some topic names will have multiple articles, depending on context. For instance, there are two articles for mount, one corresponding to its use as a command in system management (i.e., to logically attach partition or other devices to the main filesystem) and the other for use in the C programming language. Generally, the most commonly used topic is displayed by default, and there are references to any other topics with the same name in the SEE ALSO section at the bottom of the final on-screen page. The syntax to specify an article from a particular section is:
Thus, for example, the following would display the article about mount from Section 2 instead of from the default Section 8:
The -w and -W options tell man to not actually display the man pages, but to provide the location(s) of the file(s) that would be formatted or displayed. If no arguments (i.e., input files) are provided, a list of directories that is searched by man for man pages is returned. The -f option produces the same output as the whatis command. whatis provides very brief descriptions of commands from a database that is automatically created from the first line of the NAME section of each relevant man page. The -h option displays a terse summary of man‘s syntax and options. A simpler version of a man page, i.e., without backspaces and underscores, can be obtained by piping (i.e., transferring) its output to the col command used with its -b option. Thus, for example, the following would write such a version of the man page about the pstree command (which shows the processes currently on the system in a tree diagram) to a text file called pstree.txt (and create a file with this name if it did not already exist):
Unix-like operating systems often also have an additional built-in manual referred to as the Info documents, the content of which is largely identical to that of the man pages. These documents can be accessed with the info command. Although the man pages are usually viewed in a console (i.e., all-text mode) or terminal window (i.e., a text-mode window in a GUI), they can also be viewed in the Konquerer web browser, which is included with many Linux distributions. Some users might find that this provides enhanced usability, including the ability to scroll up and down an entire article regardless of its length and greater ease of changing font sizes. Any man article can be displayed in Konquerer by typing man followed by a colon and the name of the program. Thus, for example, the following would tell Konquerer to display the man page for pstree:
The Linux Information Project (LINFO) is providing an on-line alternative to the man pages with its series of articles about commonly used commands and other aspects of Linux. One major difference is that the LINFO articles are designed to be useful to users of all levels, including absolute beginners. In particular, emphasis is placed on the most useful options for commands and specific examples are often provided. An index, along with brief descriptions, of such articles about commands that have been provided to date is Index of Linux Commands.
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