Conventions Used in This Book

This book follows certain typographical conventions:


Italic is used to indicate URLs, filenames, directories, commands, options, system components (such as usernames), and to highlight comments in examples.

Constant Width

Used to show the contents of files or the output from commands.

Constant Width Bold

Used in examples and tables to show commands or other text that should be typed literally by the user.

Constant Width Italic

Used to show arguments and variables that should be replaced with user-supplied values.

#, $

Used in some examples as the root shell prompt (#) and as the user prompt ($) under the Bourne or Bash shell.


Indicates a tip, suggestion, or general note.


Indicates a warning or caution.

A final word about syntax: in many cases, the space between an option and its argument can be omitted. In other cases, the spacing (or lack of spacing) must be followed strictly. For example, -wn (no intervening space) might be interpreted differently from -w n. It’s important to notice the spacing used in option syntax.

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