\chapter*{Preface}
\addcontentsline{toc}{chapter}{Preface}

\section*{Meaning of typographic changes and symbols}

Table \ref{tab:pre_typog} describes the type changes and symbols used in this book.

\begin{table}[h]
\centering
\begin{tabular}{+l^l^l}
\hline
\rowstyle{\bfseries}
Typeface or Symbol & Meaning & Example \\
\hline
 \execout{AaBbCc123} &  The names of commands, & Edit your \execout{.bashrc} \\
 &  files, and directories; & Use \execout{ls -a} to list all files. \\
 & on-screen computer output & \execout{host\$ You have mail!}. \\
 \exec{AaBbCc123} & What you type, contrasted & \execout{host\$} \exec{su} \\
 & with on-screen computer & \\
 & output & \\
 \execsub{AaBbCc123} & Command line placeholder: & To delete a file, type  \\
 & replace with a real name & \execout{rm} \execsub{filename} \\
 & or value & \\
 \hline
\end{tabular}
\caption{Typographic Conventions}
\label{tab:pre_typog}
\end{table}
