This heading explains the working of tasks or instructions that you have just completed.

You will also find some other learning aids in the book, including:

These are short multiple choice questions intended to help you test your own understanding.

These set practical challenges and give you ideas for experimenting with what you have learned.

You will also find a number of styles of text that distinguish between different kinds of information. Here are some examples of these styles, and an explanation of their meaning.

Code words in text are shown as follows: "We can include other contexts through the use of the include directive."

A block of code is set as follows:

/usr/bin/rrdtool graph -
--imgformat=PNG
--start=-86400
--end=-300

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

   $temp = array(
        "ntop_header" => array(
                "friendly_name" => "NTop",
         "method" => "spacer",
         ),

Any command-line input or output is written as follows:

perl create_rrdfile_linux.pl test.rrd

New terms and important words are shown in bold. Words that you see on the screen, in menus or dialog boxes, for example, appear in the text like this: "Go back to the device overview page by clicking on the Devices link under the Management menu".