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<H1></H1>



<UL>

	<LI><A HREF="#Heading1">- 8 -</A>

	<UL>

		<LI><A HREF="#Heading2">File System</A>

		<UL>

			<LI><A HREF="#Heading3">Files: An Overview</A>

			<UL>

				<LI><A HREF="#Heading4">Common Types of Files</A>

				<LI><A HREF="#Heading5">Filenames</A>

			</UL>

			<LI><A HREF="#Heading6">Directories: An Overview</A>

			<UL>

				<LI><A HREF="#Heading7">Parent Directories and Subdirectories</A>

				<LI><A HREF="#Heading8">The Root Directory</A>

				<LI><A HREF="#Heading9">How Directories Are Named</A>

				<LI><A HREF="#Heading10">The Home Directory</A>

			</UL>

			<LI><A HREF="#Heading11">WARNING</A>

			<LI><A HREF="#Heading12">Navigating the Linux File System</A>

			<UL>

				<LI><A HREF="#Heading13">The pwd Command: Where Am I?</A>

				<LI><A HREF="#Heading14">Absolute and Relative Filenames</A>

				<LI><A HREF="#Heading15">Going Places: The cd Command</A>

				<LI><A HREF="#Heading16">Theres No Place Like Home</A>

			</UL>

			<LI><A HREF="#Heading17">TIP</A>

			<LI><A HREF="#Heading18">Creating and Deleting Files</A>

			<LI><A HREF="#Heading19">WARNING</A>

			<UL>

				<LI><A HREF="#Heading20">cat: That Useful Feline</A>

			</UL>

			<LI><A HREF="#Heading21">NOTE</A>

			<UL>

				<LI><A HREF="#Heading22">Creating Directories</A>

			</UL>

			<LI><A HREF="#Heading23">TIP</A>

			<UL>

				<LI><A HREF="#Heading24">Moving and Copying Files</A>

			</UL>

			<LI><A HREF="#Heading25">WARNING</A>

			<UL>

				<LI><A HREF="#Heading26">Moving and Copying with Wildcards</A>

			</UL>

			<LI><A HREF="#Heading27">NOTE</A>

			<UL>

				<LI><A HREF="#Heading28">Moving Directories</A>

			</UL>

			<LI><A HREF="#Heading29">NOTE</A>

			<LI><A HREF="#Heading30">Removing Files and Directories</A>

			<LI><A HREF="#Heading31">WARNING</A>

			<UL>

				<LI><A HREF="#Heading32">Removing Directories</A>

			</UL>

			<LI><A HREF="#Heading33">TIP</A>

			<LI><A HREF="#Heading34">WARNING</A>

			<LI><A HREF="#Heading35">File Permissions and Ownership</A>

			<UL>

				<LI><A HREF="#Heading36">File and Directory Ownership</A>

				<LI><A HREF="#Heading37">File Permissions</A>

			</UL>

			<LI><A HREF="#Heading38">TIP</A>

			<LI><A HREF="#Heading39">NOTE</A>

			<LI><A HREF="#Heading40">WARNING</A>

			<UL>

				<LI><A HREF="#Heading41">Changing File Permissions</A>

				<LI><A HREF="#Heading42">Changing Directory Permissions</A>

			</UL>

			<LI><A HREF="#Heading43">WARNING</A>

			<LI><A HREF="#Heading44">Miscellaneous File Commands</A>

			<UL>

				<LI><A HREF="#Heading45">Fear of Compression: The Zipless File</A>

				<LI><A HREF="#Heading46">How to tar Without Feathering</A>

			</UL>

			<LI><A HREF="#Heading47">WARNING</A>

			<LI><A HREF="#Heading48">NOTE</A>

			<LI><A HREF="#Heading49">Important Directories in the Linux File System</A>

			<UL>

				<LI><A HREF="#Heading50">/</A>

				<LI><A HREF="#Heading51">/home</A>

				<LI><A HREF="#Heading52">/bin</A>

				<LI><A HREF="#Heading53">/usr</A>

				<LI><A HREF="#Heading54">/usr/bin</A>

				<LI><A HREF="#Heading55">/usr/spool</A>

				<LI><A HREF="#Heading56">/dev</A>

				<LI><A HREF="#Heading57">/usr/sbin</A>

				<LI><A HREF="#Heading58">/sbin</A>

				<LI><A HREF="#Heading59">/etc</A>

			</UL>

			<LI><A HREF="#Heading60">Summary</A>

		</UL>

	</UL>

</UL>



<P>

<HR SIZE="4">



<H2 ALIGN="CENTER"><A NAME="Heading1<FONT COLOR="#000077">- 8 -</FONT></H2>

<H2 ALIGN="CENTER"><A NAME="Heading2<FONT COLOR="#000077">File System</FONT></H2>

<P><I>by Ed Treijs</I></P>



<P>IN THIS CHAPTER</P>



<UL>

	<LI>Files: An Overview 116

	<P>

	<LI>Directories: An Overview 117

	<P>

	<LI>Navigating the Linux File System 119

	<P>

	<LI>Creating and Deleting Files 122

	<P>

	<LI>Removing Files and Directories 127

	<P>

	<LI>File Permissions and Ownership 130

	<P>

	<LI>Miscellaneous File Commands 134

	<P>

	<LI>Important Directories in the Linux File System 135

</UL>



<P><BR>

In this chapter, you learn about



<UL>

	<LI>Files: what they are, types of files, filenames

	<P>

	<LI>Directories: what they are, parent directories and subdirectories, directory

	names, your home directory

	<P>

	<LI>Absolute and relative file and directory names

	<P>

	<LI>Moving between directories using the <TT>cd</TT> command

	<P>

	<LI>Using the <TT>cat</TT> command to create a new file

	<P>

	<LI>Creating directories

	<P>

	<LI>Moving and copying files

	<P>

	<LI>Removing files and directories

	<P>

	<LI>File and directory ownership, using <TT>chown</TT> and <TT>chgrp</TT> to change

	ownership

	<P>

	<LI>File and directory permissions, using <TT>chmod</TT> to change permissions

	<P>

	<LI>Using the <TT>gunzip</TT> command to uncompress <TT>.gz</TT> files compressed

	by <TT>gzip</TT>

	<P>

	<LI>The <TT>tar</TT> command

	<P>

	<LI>The standard Linux directories and directory structure

</UL>



<P>To understand how Linux works, and to use the system beyond a superficial level,

you must be familiar with the Linux notion of files and the file system into which

they are organized.

<H3 ALIGN="CENTER"><A NAME="Heading3<FONT COLOR="#000077">Files: An Overview</FONT></H3>

<P>The most basic concept of a file, and one you may already be familiar with from

other computer systems, defines a file as a distinct chunk of information that is

found on your hard drive. Distinct means that there can be many different files,

each with its own particular contents. To keep files from getting confused with each

other, every file must have a unique identity. In Linux, you identify each file by

its name and location. In each location or directory, there can be only one file

by a particular name. So, for instance, if you create a file called <TT>novel</TT>,

and you get a second great idea, you will either have to call it something different,

such as <TT>novel2</TT>, or put it in a different place, to keep from overwriting

the contents already in your original <TT>novel</TT>.

<H4 ALIGN="CENTER"><A NAME="Heading4<FONT COLOR="#000077">Common Types of Files</FONT></H4>

<P>Files can contain various types of information. The following three types will

become the most familiar to you:



<UL>

	<LI>User data: Information that you create and update. The very simplest user data

	is plain text or numbers. You learn to create these simple files later in this chapter.

	More complicated user data files might have to be interpreted by another program

	to make sense. For instance, a spreadsheet file looks like gibberish if you look

	at it directly. To work with a spreadsheet, you have to start up the spreadsheet

	program and read in the spreadsheet file.

	<P>

	<LI>System data: Information, often in plain text form, that is read and used by

	the Linux system--to keep track of which users are allowed on the system, for instance.

	As a system administrator, you are responsible for changing system data files. For

	instance, when you create a new user, you modify the file <TT>/etc/passwd</TT>, which

	contains the user information. Ordinary users of the system are usually not concerned

	with system data files, except for their private startup files.

	<P>

	<LI>Executable files: These files contain instructions that your computer can perform.

	This set of instructions is often called a program. When you tell the computer to

	perform them, you're telling it to execute the instructions given to it. To human

	eyes, executable files contain meaningless gibberish--obviously your computer doesn't

	think the way you do! Creating or modifying executable files takes special tools.

	You learn how to use these programming tools in Part V, &quot;Linux for Programmers.&quot;

</UL>



<H4 ALIGN="CENTER"><A NAME="Heading5<FONT COLOR="#000077">Filenames</FONT></H4>

<P>Linux allows filenames to be up to 256 characters long. These characters can be

lower- and uppercase letters, numbers, and other characters, usually the dash (-),

the underscore (_), and the dot (.).</P>

<P>They can't include reserved metacharacters such as the asterisk, question mark,

backslash, and space, because these all have meaning to the shell. We met some metacharacters

when we discussed wildcards in the previous chapter. Other metacharacters will be

introduced in the Linux shell chapters.

<H3 ALIGN="CENTER"><A NAME="Heading6<FONT COLOR="#000077">Directories: An Overview</FONT></H3>

<P>Linux, like many other computer systems, organizes files in directories. You can

think of directories as file folders and their contents as the files. However, there

is one absolutely crucial difference between the Linux file system and an office

filing system. In the office, file folders usually don't contain other file folders.

In Linux, file folders can contain other file folders. In fact, there is no Linux

&quot;filing cabinet&quot;--just a huge file folder that holds some files and other

folders. These folders contain files and possibly other folders in turn, and so on.

<H4 ALIGN="CENTER"><A NAME="Heading7<FONT COLOR="#000077">Parent Directories

and Subdirectories</FONT></H4>

<P>Imagine a scenario in which you have a directory, A, that contains another directory,

B. Directory B is then a subdirectory of directory A, and directory A is the parent

directory of directory B. You will see these terms often, both in this book and elsewhere.

<H4 ALIGN="CENTER"><A NAME="Heading8<FONT COLOR="#000077">The Root Directory</FONT></H4>

<P>In Linux, the directory that holds all the other directories is called the root

directory. This is the ultimate parent directory; every other directory is some level

of subdirectory.</P>

<P>From the root directory, the whole structure of directory upon directory springs

and grows like some electronic elm. This is called a tree structure because, from

the single root directory, directories and subdirectories branch off like tree limbs.

<H4 ALIGN="CENTER"><A NAME="Heading9<FONT COLOR="#000077">How Directories Are

Named</FONT></H4>

<P>Directories are named just like files, and they can contain upper- and lowercase

letters, numbers, and characters such as <TT>-</TT>, <TT>.</TT>, and <TT>_</TT>.</P>

<P>The slash (<TT>/</TT>) character is used to show files or directories within other

directories. For instance, <TT>usr/bin</TT> means that <TT>bin</TT> is found in the

<TT>usr</TT> directory. Note that you can't tell, from this example, whether <TT>bin</TT>

is a file or a directory, although you know that <TT>usr</TT> must be a directory

because it holds another item--namely, <TT>bin</TT>. When you see <TT>usr/bin/grep</TT>,

you know that both <TT>usr</TT> and <TT>bin</TT> must be directories, but again,

you can't be sure about <TT>grep</TT>. The <TT>ls</TT> program shows directories

with a following /--for example, <TT>fido/</TT>. This notation implies that you could

have, for instance, <TT>fido/file</TT>; therefore, <TT>fido</TT> must be a directory.</P>

<P>The root directory is shown simply by the symbol <TT>/</TT> rather than mentioned

by name. It's very easy to tell when <TT>/</TT> is used to separate directories and

when it's used to signify the root directory. If <TT>/</TT> has no name before it,

it stands for the root directory. For example, <TT>/usr</TT> means that the <TT>usr</TT>

subdirectory is found in the root directory, and <TT>/usr/bin</TT> means that <TT>bin</TT>

is found in the <TT>usr</TT> directory and that <TT>usr</TT> is a subdirectory of

the root directory. Remember, by definition the root directory can't be a subdirectory.

<H4 ALIGN="CENTER"><A NAME="Heading10<FONT COLOR="#000077">The Home Directory</FONT></H4>

<P>Linux provides each user with his or her own directory, called the home directory.

Within this home directory, users can store their own files and create subdirectories.

Users generally have complete control over what's found in their home directories.

Because there are usually no Linux system files or files belonging to other users

in your home directory, you can create, name, move, and delete files and directories

as you see fit.



<DL>