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<?xml version="1.0" encoding="iso-8859-1"?>
<!--
     The FreeBSD Documentation Project

     $FreeBSD$
-->
<chapter xmlns="http://docbook.org/ns/docbook"
  xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
  xml:id="basics">
  <!--
  <chapterinfo>
    <authorgroup>
      <author>
	<firstname>Chris</firstname>
	<surname>Shumway</surname>
	<contrib>Rewritten by in Mar 2000</contrib>
      </author>
    </authorgroup>
  </chapterinfo>
  -->
  <title>&os; Basics</title>

  <sect1 xml:id="basics-synopsis">
    <title>Synopsis</title>

    <para>This chapter covers the basic commands and functionality of
      the &os; operating system.  Much of this material is relevant
      for any &unix;-like operating system.  New &os; users are
      encouraged to read through this chapter carefully.</para>

    <para>After reading this chapter, you will know:</para>

    <itemizedlist>
      <listitem>
	<para>How to use and configure virtual consoles.</para>
      </listitem>

      <listitem>
	<para>How to create and manage users and groups on
	  &os;.</para>
      </listitem>

      <listitem>
	<para>How &unix; file permissions and &os; file flags
	  work.</para>
      </listitem>

      <listitem>
	<para>The default &os; file system layout.</para>
      </listitem>

      <listitem>
	<para>The &os; disk organization.</para>
      </listitem>

      <listitem>
	<para>How to mount and unmount file systems.</para>
      </listitem>

      <listitem>
	<para>What processes, daemons, and signals are.</para>
      </listitem>

      <listitem>
	<para>What a shell is, and how to change the default login
	  environment.</para>
      </listitem>

      <listitem>
	<para>How to use basic text editors.</para>
      </listitem>

      <listitem>
	<para>What devices and device nodes are.</para>
      </listitem>

      <listitem>
	<para>How to read manual pages for more information.</para>
      </listitem>
    </itemizedlist>
  </sect1>

  <sect1 xml:id="consoles">
    <title>Virtual Consoles and Terminals</title>

    <indexterm>
      <primary>virtual consoles</primary>
    </indexterm>
    <indexterm>
      <primary>terminals</primary>
    </indexterm>
    <indexterm>
      <primary>console</primary>
    </indexterm>

    <para>Unless &os; has been configured to automatically start a
      graphical environment during startup, the system will boot
      into a command line login prompt, as seen in this
      example:</para>

    <screen>FreeBSD/amd64 (pc3.example.org) (ttyv0)

login:</screen>

    <para>The first line contains some information about the system.
      The <literal>amd64</literal> indicates that the system in this
      example is running a 64-bit version of &os;.  The hostname is
      <systemitem>pc3.example.org</systemitem>, and
      <filename>ttyv0</filename> indicates that this is the
      <quote>system console</quote>.  The second line is the login
      prompt.</para>

    <para>Since &os; is a multiuser system, it needs some way to
      distinguish between different users.  This is accomplished by
      requiring every user to log into the system before gaining
      access to the programs on the system.  Every user has a
      unique name <quote>username</quote> and a personal
      <quote>password</quote>.</para>

    <para>To log into the system console, type the username that
      was configured during system installation, as described in
      <xref linkend="bsdinstall-addusers"/>, and press
      <keycap>Enter</keycap>.  Then enter the password associated
      with the username and press <keycap>Enter</keycap>.  The
      password is <emphasis>not echoed</emphasis> for security
      reasons.</para>

    <para>Once the correct password is input, the message of the
      day (<acronym>MOTD</acronym>) will be displayed followed
      by a command prompt.  Depending upon the shell that was
      selected when the user was created, this prompt will be a
      <literal>#</literal>, <literal>$</literal>, or
      <literal>%</literal> character.  The prompt indicates that
      the user is now logged into the &os; system console and ready
      to try the available commands.</para>

    <sect2 xml:id="consoles-virtual">
      <title>Virtual Consoles</title>

      <para>While the system console can be used to interact with
	the system, a user working from the command line at the
	keyboard of a &os; system will typically instead log into a
	virtual console.  This is because system messages are
	configured by default to display on the system console.
	These messages will appear over the command or file that the
	user is working on, making it difficult to concentrate on
	the work at hand.</para>

      <para>By default, &os; is configured to provide several virtual
	consoles for inputting commands.  Each virtual console has
	its own login prompt and shell and it is easy to switch
	between virtual consoles.  This essentially provides the
	command line equivalent of having several windows open at the
	same time in a graphical environment.</para>

      <para>The key combinations
	<keycombo><keycap>Alt</keycap><keycap>F1</keycap></keycombo>
	through
	<keycombo><keycap>Alt</keycap><keycap>F8</keycap></keycombo>
	have been reserved by &os; for switching between virtual
	consoles.  Use
	<keycombo><keycap>Alt</keycap><keycap>F1</keycap></keycombo>
	to switch to the system console
	(<filename>ttyv0</filename>),
	<keycombo><keycap>Alt</keycap><keycap>F2</keycap></keycombo>
	to access the first virtual console
	(<filename>ttyv1</filename>),
	<keycombo><keycap>Alt</keycap><keycap>F3</keycap></keycombo>
	to access the second virtual console
	(<filename>ttyv2</filename>), and so on.
	When using <application>&xorg;</application> as a graphical
	console, the combination becomes <keycombo>
	  <keycap>Ctrl</keycap><keycap>Alt</keycap><keycap>F1</keycap>
	</keycombo> to return to a text-based virtual console.</para>

      <para>When switching from one console to the next, &os;
	manages the screen output.  The result is an illusion of
	having multiple virtual screens and keyboards that can be used
	to type commands for &os; to run.  The programs that are
	launched in one virtual console do not stop running when
	the user switches to a different virtual console.</para>

      <para>Refer to &man.kbdcontrol.1;, &man.vidcontrol.1;,
	&man.atkbd.4;, &man.syscons.4;, and &man.vt.4; for a more
	technical description of the &os; console and its keyboard
	drivers.</para>

      <para>In &os;, the number of available virtual consoles is
	configured in this section of
	<filename>/etc/ttys</filename>:</para>

      <programlisting># name    getty                         type  status comments
#
ttyv0   "/usr/libexec/getty Pc"         xterm   on  secure
# Virtual terminals
ttyv1   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv2   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv3   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv4   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv5   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv6   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv7   "/usr/libexec/getty Pc"         xterm   on  secure
ttyv8   "/usr/X11R6/bin/xdm -nodaemon"  xterm   off secure</programlisting>


      <para>To disable a virtual console, put a comment symbol
	(<literal>#</literal>) at the beginning of the line
	representing that virtual console.  For example, to reduce the
	number of available virtual consoles from eight to four, put a
	<literal>#</literal> in front of the last four lines
	representing virtual consoles <filename>ttyv5</filename>
	through <filename>ttyv8</filename>.
	<emphasis>Do not</emphasis> comment out the line for the
	system console <filename>ttyv0</filename>.  Note that the last
	virtual console (<filename>ttyv8</filename>) is used to access
	the graphical environment if <application>&xorg;</application>
	has been installed and configured as described in
	<xref linkend="x11"/>.</para>

      <para>For a detailed description of every column in this file
	and the available options for the virtual consoles, refer to
	&man.ttys.5;.</para>
    </sect2>

    <sect2 xml:id="consoles-singleuser">
      <title>Single User Mode</title>

      <para>The &os; boot menu provides an option labelled as
	<quote>Boot Single User</quote>.  If this option is selected,
	the system will boot into a special mode known as
	<quote>single user mode</quote>.  This mode is typically used
	to repair a system that will not boot or to reset the
	<systemitem class="username">root</systemitem> password when
	it is not known.  While in single user mode, networking and
	other virtual consoles are not available.  However, full
	<systemitem class="username">root</systemitem> access to the
	system is available, and by default, the
	<systemitem class="username">root</systemitem> password is not
	needed.  For these reasons, physical access to the keyboard is
	needed to boot into this mode and determining who has physical
	access to the keyboard is something to consider when securing
	a &os; system.</para>

      <para>The settings which control single user mode are found in
	this section of <filename>/etc/ttys</filename>:</para>

      <programlisting># name  getty                           type  status  comments
#
# If console is marked "insecure", then init will ask for the root password
# when going to single-user mode.
console none                            unknown  off  secure</programlisting>

      <para>By default, the status is set to
	<literal>secure</literal>.  This assumes that who has physical
	access to the keyboard is either not important or it is
	controlled by a physical security policy.  If this setting is
	changed to <literal>insecure</literal>, the assumption is that
	the environment itself is insecure because anyone can access
	the keyboard.  When this line is changed to
	<literal>insecure</literal>, &os; will prompt for the
	<systemitem class="username">root</systemitem> password when a
	user selects to boot into single user mode.</para>

      <note>
	<para><emphasis>Be careful when changing this setting to
	    <literal>insecure</literal></emphasis>!  If the
	  <systemitem class="username">root</systemitem> password is
	  forgotten, booting into single user mode is still possible,
	  but may be difficult for someone who is not familiar with
	  the &os; booting process.</para>
      </note>
    </sect2>

    <sect2 xml:id="consoles-vidcontrol">
      <title>Changing Console Video Modes</title>

      <para>The &os; console default video mode may be adjusted to
	1024x768, 1280x1024, or any other size supported by the
	graphics chip and monitor.  To use a different video mode
	load the <literal>VESA</literal> module:</para>

      <screen>&prompt.root; <userinput>kldload vesa</userinput></screen>

      <para>To determine which video modes are supported by the
	hardware, use &man.vidcontrol.1;.  To get a list of supported
	video modes issue the following:</para>

      <screen>&prompt.root; <userinput>vidcontrol -i mode</userinput></screen>

      <para>The output of this command lists the video modes that are
	supported by the hardware.  To select a new video mode,
	specify the mode using &man.vidcontrol.1; as the
	<systemitem class="username">root</systemitem> user:</para>

      <screen>&prompt.root; <userinput>vidcontrol MODE_279</userinput></screen>

      <para>If the new video mode is acceptable, it can be permanently
	set on boot by adding it to
	<filename>/etc/rc.conf</filename>:</para>

      <programlisting>allscreens_flags="MODE_279"</programlisting>
    </sect2>
  </sect1>

    <!--
  <chapterinfo>
    <authorgroup>
      <author>
	<firstname>Neil</firstname>
	<surname>Blakey-Milner</surname>
	<contrib>Contributed by in Feb 2000</contrib>
      </author>
    </authorgroup>
  </chapterinfo>
  -->

  <sect1 xml:id="users-synopsis">
    <title>Users and Basic Account Management</title>

    <para>&os; allows multiple users to use the computer at the same
      time.  While only one user can sit in front of the screen and
      use the keyboard at any one time, any number of users can log
      in to the system through the network.  To use the system, each
      user should have their own user account.</para>

    <para>This chapter describes:</para>

    <itemizedlist>
      <listitem>
	<para>The different types of user accounts on a
	  &os; system.</para>
      </listitem>

      <listitem>
	<para>How to add, remove, and modify user accounts.</para>
      </listitem>

      <listitem>
	<para>How to set limits to control the
	  resources that users and
	  groups are allowed to access.</para>
      </listitem>

      <listitem>
	<para>How to create groups and add users as members of a
	  group.</para>
      </listitem>
    </itemizedlist>

    <sect2 xml:id="users-introduction">
      <title>Account Types</title>

      <para>Since all access to the &os; system is achieved using
	accounts and all processes are run by users, user and account
	management is important.</para>

      <para>There are three main types of accounts: system accounts,
	user accounts, and the superuser account.</para>

      <sect3 xml:id="users-system">
	<title>System Accounts</title>

	<indexterm>
	  <primary>accounts</primary>
	  <secondary>system</secondary>
	</indexterm>

	<para>System accounts are used to run services such as DNS,
	  mail, and web servers.  The reason for this is security; if
	  all services ran as the superuser, they could act without
	  restriction.</para>

	<indexterm>
	  <primary>accounts</primary>
	  <secondary><systemitem
	      class="username">daemon</systemitem></secondary>
	</indexterm>
	<indexterm>
	  <primary>accounts</primary>
	  <secondary><systemitem
	      class="username">operator</systemitem></secondary>
	</indexterm>

	<para>Examples of system accounts are
	  <systemitem class="username">daemon</systemitem>,
	  <systemitem class="username">operator</systemitem>,
	  <systemitem class="username">bind</systemitem>,
	  <systemitem class="username">news</systemitem>, and
	  <systemitem class="username">www</systemitem>.</para>

	<warning>
	  <para>Care must be taken when using the operator group, as
	    unintended superuser-like access privileges may be
	    granted, including but not limited to shutdown, reboot,
	    and access to all items in <filename>/dev</filename>
	    in the group.</para>
	</warning>

	<indexterm>
	  <primary>accounts</primary>
	  <secondary><systemitem
	      class="username">nobody</systemitem></secondary>
	</indexterm>

	<para><systemitem class="username">nobody</systemitem> is the
	  generic unprivileged system account.  However, the more
	  services that use
	  <systemitem class="username">nobody</systemitem>, the more
	  files and processes that user will become associated with,
	  and hence the more privileged that user becomes.</para>
      </sect3>

      <sect3 xml:id="users-user">
	<title>User Accounts</title>

	<indexterm>
	  <primary>accounts</primary>
	  <secondary>user</secondary>
	</indexterm>

	<para>User accounts are assigned to real people and are used
	  to log in and use the system.  Every person accessing the
	  system should have a unique user account.  This allows the
	  administrator to find out who is doing what and prevents
	  users from clobbering the settings of other users.</para>

	<para>Each user can set up their own environment to
	  accommodate their use of the system, by configuring their
	  default shell, editor, key bindings, and language
	  settings.</para>

	<para>Every user account on a &os; system has certain
	  information associated with it:</para>

	<variablelist>
	  <varlistentry>
	    <term>User name</term>

	    <listitem>
	      <para>The user name is typed at the
		<prompt>login:</prompt> prompt.  Each user must have
		a unique user name.  There are a number of rules for
		creating valid user names which are documented in
		&man.passwd.5;.  It is recommended to use user names
		that consist of eight or fewer, all lower case
		characters in order to maintain backwards
		compatibility with applications.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>Password</term>

	    <listitem>
	      <para>Each account has an associated password.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>User ID (<acronym>UID</acronym>)</term>

	    <listitem>
	      <para>The User ID (<acronym>UID</acronym>) is a number
		used to uniquely identify the user to the &os; system.
		Commands that allow a user name to be specified will
		first convert it to the <acronym>UID</acronym>.  It is
		recommended to use a UID less than 65535, since higher
		values may cause compatibility issues with some
		software.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>Group ID (<acronym>GID</acronym>)</term>

	    <listitem>
	      <para>The Group ID (<acronym>GID</acronym>) is a number
		used to uniquely identify the primary group that the
		user belongs to.  Groups are a mechanism for
		controlling access to resources based on a user's
		<acronym>GID</acronym> rather than their
		<acronym>UID</acronym>.  This can significantly reduce
		the size of some configuration files and allows users
		to be members of more than one group.  It is
		recommended to use a GID of 65535 or lower as higher
		GIDs may break some software.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>Login class</term>

	    <listitem>
	      <para>Login classes are an extension to the group
		mechanism that provide additional flexibility when
		tailoring the system to different users.  Login
		classes are discussed further in
		<xref linkend="users-limiting"/>.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>Password change time</term>

	    <listitem>
	      <para>By default, passwords do not expire.  However,
		password expiration can be enabled on a per-user
		basis, forcing some or all users to change their
		passwords after a certain amount of time has
		elapsed.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>Account expiration time</term>

	    <listitem>
	      <para>By default, &os; does not expire accounts.  When
		creating accounts that need a limited lifespan, such
		as student accounts in a school, specify the account
		expiry date using &man.pw.8;.  After the expiry time
		has elapsed, the account cannot be used to log in to
		the system, although the account's directories and
		files will remain.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>User's full name</term>

	    <listitem>
	      <para>The user name uniquely identifies the account to
		&os;, but does not necessarily reflect the user's real
		name.  Similar to a comment, this information can
		contain spaces, uppercase characters, and be more
		than 8 characters long.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>Home directory</term>

	    <listitem>
	      <para>The home directory is the full path to a directory
		on the system.  This is the user's starting directory
		when the user logs in.  A common convention is to put
		all user home directories under <filename
		  ><replaceable>/home/username</replaceable></filename>
		or <filename
		  ><replaceable>/usr/home/username</replaceable></filename>.
		Each user stores their personal files and
		subdirectories in their own home directory.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>User shell</term>

	    <listitem>
	      <para>The shell provides the user's default environment
		for interacting with the system.  There are many
		different kinds of shells and experienced users will
		have their own preferences, which can be reflected in
		their account settings.</para>
	    </listitem>
	  </varlistentry>
	</variablelist>
      </sect3>

      <sect3 xml:id="users-superuser">
	<title>The Superuser Account</title>

	<indexterm>
	  <primary>accounts</primary>
	  <secondary>superuser (root)</secondary>
	</indexterm>

	<para>The superuser account, usually called
	  <systemitem class="username">root</systemitem>, is used to
	  manage the system with no limitations on privileges.  For
	  this reason, it should not be used for day-to-day tasks like
	  sending and receiving mail, general exploration of the
	  system, or programming.</para>

	<para>The superuser, unlike other user accounts, can operate
	  without limits, and misuse of the superuser account may
	  result in spectacular disasters.  User accounts are unable
	  to destroy the operating system by mistake, so it is
	  recommended to login as a user account and to only become
	  the superuser when a command requires extra
	  privilege.</para>

	<para>Always double and triple-check any commands issued as
	  the superuser, since an extra space or missing character can
	  mean irreparable data loss.</para>

	<para>There are several ways to gain superuser privilege.
	  While one can log in as
	  <systemitem class="username">root</systemitem>, this is
	  highly discouraged.</para>

	<para>Instead, use &man.su.1; to become the superuser.  If
	  <literal>-</literal> is specified when running this command,
	  the user will also inherit the root user's environment.  The
	  user running this command must be in the
	  <systemitem class="groupname">wheel</systemitem> group or
	  else the command will fail.  The user must also know the
	  password for the
	  <systemitem class="username">root</systemitem> user
	  account.</para>

	<para>In this example, the user only becomes superuser in
	  order to run <command>make install</command> as this step
	  requires superuser privilege.  Once the command completes,
	  the user types <command>exit</command> to leave the
	  superuser account and return to the privilege of their user
	  account.</para>

	<example>
	  <title>Install a Program As the Superuser</title>

	  <screen>&prompt.user; <userinput>configure</userinput>
&prompt.user; <userinput>make</userinput>
&prompt.user; <userinput>su -</userinput>
Password:
&prompt.root; <userinput>make install</userinput>
&prompt.root; <userinput>exit</userinput>
&prompt.user;</screen>
	</example>

	<para>The built-in &man.su.1; framework works well for single
	  systems or small networks with just one system
	  administrator.  An alternative is to install the
	  <package>security/sudo</package> package or port.  This
	  software provides activity logging and allows the
	  administrator to configure which users can run which
	  commands as the superuser.</para>
      </sect3>
    </sect2>

    <sect2 xml:id="users-modifying">
      <title>Managing Accounts</title>

      <indexterm>
	<primary>accounts</primary>
	<secondary>modifying</secondary>
      </indexterm>

      <para>&os; provides a variety of different commands to manage
	user accounts.  The most common commands are summarized in
	<xref linkend="users-modifying-utilities"/>, followed by some
	examples of their usage.  See the manual page for each utility
	for more details and usage examples.</para>

      <table frame="none" pgwide="1"
	xml:id="users-modifying-utilities">
	<title>Utilities for Managing User Accounts</title>

	<tgroup cols="2">
	  <colspec colwidth="1*"/>
	  <colspec colwidth="2*"/>

	  <thead>
	    <row>
	      <entry>Command</entry>
	      <entry>Summary</entry>
	    </row>
	  </thead>
	  <tbody>
	    <row>
	      <entry>&man.adduser.8;</entry>
	      <entry>The recommended command-line application for
		adding new users.</entry>
	    </row>

	    <row>
	      <entry>&man.rmuser.8;</entry>
	      <entry>The recommended command-line application for
		removing users.</entry>
	    </row>

	    <row>
	      <entry>&man.chpass.1;</entry>
	      <entry>A flexible tool for changing user database
		information.</entry>
	    </row>

	    <row>
	      <entry>&man.passwd.1;</entry>
	      <entry>The command-line tool to change user
		passwords.</entry>
	    </row>

	    <row>
	      <entry>&man.pw.8;</entry>
	      <entry>A powerful and flexible tool for modifying all
		aspects of user accounts.</entry>
	    </row>
	  </tbody>
	</tgroup>
      </table>

      <sect3 xml:id="users-adduser">
	<title><command>adduser</command></title>

	<indexterm>
	  <primary>accounts</primary>
	  <secondary>adding</secondary>
	</indexterm>
	<indexterm>
	  <primary><command>adduser</command></primary>
	</indexterm>
	<indexterm>
	  <primary><filename>/usr/share/skel</filename></primary>
	</indexterm>
	<indexterm>
	  <primary>skeleton directory</primary>
	</indexterm>

	<para>The recommended program for adding new users is
	  &man.adduser.8;.  When a new user is added, this program
	  automatically updates <filename>/etc/passwd</filename> and
	  <filename>/etc/group</filename>.  It also creates a home
	  directory for the new user, copies in the default
	  configuration files from
	  <filename>/usr/share/skel</filename>, and can optionally
	  mail the new user a welcome message.  This utility must be
	  run as the superuser.</para>

	<para>The &man.adduser.8; utility is interactive and walks
	  through the steps for creating a new user account.  As seen
	  in <xref linkend="users-modifying-adduser"/>, either input
	  the required information or press <keycap>Return</keycap>
	  to accept the default value shown in square brackets.
	  In this example, the user has been invited into the
	  <systemitem class="groupname">wheel</systemitem> group,
	  allowing them to become the superuser with &man.su.1;.
	  When finished, the utility will prompt to either
	  create another user or to exit.</para>

	<example xml:id="users-modifying-adduser">
	  <title>Adding a User on &os;</title>

	  <screen>&prompt.root; <userinput>adduser</userinput>
Username: <userinput>jru</userinput>
Full name: <userinput>J. Random User</userinput>
Uid (Leave empty for default):
Login group [jru]:
Login group is jru. Invite jru into other groups? []: <userinput>wheel</userinput>
Login class [default]:
Shell (sh csh tcsh zsh nologin) [sh]: <userinput>zsh</userinput>
Home directory [/home/jru]:
Home directory permissions (Leave empty for default):
Use password-based authentication? [yes]:
Use an empty password? (yes/no) [no]:
Use a random password? (yes/no) [no]:
Enter password:
Enter password again:
Lock out the account after creation? [no]:
Username   : jru
Password   : ****
Full Name  : J. Random User
Uid        : 1001
Class      :
Groups     : jru wheel
Home       : /home/jru
Shell      : /usr/local/bin/zsh
Locked     : no
OK? (yes/no): <userinput>yes</userinput>
adduser: INFO: Successfully added (jru) to the user database.
Add another user? (yes/no): <userinput>no</userinput>
Goodbye!
&prompt.root;</screen>
	</example>

	<note>
	  <para>Since the password is not echoed when typed, be
	    careful to not mistype the password when creating the user
	    account.</para>
	</note>
      </sect3>

      <sect3 xml:id="users-rmuser">
	<title><command>rmuser</command></title>

	<indexterm>
	  <primary><command>rmuser</command></primary>
	</indexterm>
	<indexterm>
	  <primary>accounts</primary>
	  <secondary>removing</secondary>
	</indexterm>

	<para>To completely remove a user from the system, run
	  &man.rmuser.8; as the superuser.  This command performs the
	  following steps:</para>

	<procedure>
	  <step>
	    <para>Removes the user's &man.crontab.1; entry, if one
	      exists.</para>
	  </step>

	  <step>
	    <para>Removes any &man.at.1; jobs belonging to the
	      user.</para>
	  </step>

	  <step>
	    <para>Kills all processes owned by the user.</para>
	  </step>

	  <step>
	    <para>Removes the user from the system's local password
	      file.</para>
	  </step>

	  <step>
	    <para>Optionally removes the user's home directory, if it
	      is owned by the user.</para>
	  </step>

	  <step>
	    <para>Removes the incoming mail files belonging to the
	      user from <filename>/var/mail</filename>.</para>
	  </step>

	  <step>
	    <para>Removes all files owned by the user from temporary
	      file storage areas such as
	      <filename>/tmp</filename>.</para>
	  </step>

	  <step>
	    <para>Finally, removes the username from all groups to
	      which it belongs in <filename>/etc/group</filename>.  If
	      a group becomes empty and the group name is the same as
	      the username, the group is removed.  This complements
	      the per-user unique groups created by
	      &man.adduser.8;.</para>
	  </step>
	</procedure>

	<para>&man.rmuser.8; cannot be used to remove superuser
	  accounts since that is almost always an indication of
	  massive destruction.</para>

	<para>By default, an interactive mode is used, as shown
	  in the following example.</para>

	<example>
	  <title><command>rmuser</command> Interactive Account
	    Removal</title>

	  <screen>&prompt.root; <userinput>rmuser jru</userinput>
Matching password entry:
jru:*:1001:1001::0:0:J. Random User:/home/jru:/usr/local/bin/zsh
Is this the entry you wish to remove? <userinput>y</userinput>
Remove user's home directory (/home/jru)? <userinput>y</userinput>
Removing user (jru): mailspool home passwd.
&prompt.root;</screen>
	</example>
      </sect3>

      <sect3 xml:id="users-chpass">
	<title><command>chpass</command></title>

	<indexterm>
	  <primary><command>chpass</command></primary>
	</indexterm>

	<para>Any user can use &man.chpass.1; to change their default
	  shell and personal information associated with their user
	  account.  The superuser can use this utility to change
	  additional account information for any user.</para>

	<para>When passed no options, aside from an optional username,
	  &man.chpass.1; displays an editor containing user
	  information.  When the user exits from the editor, the user
	  database is updated with the new information.</para>

	<note>
	  <para>This utility will prompt for the user's password when
	    exiting the editor, unless the utility is run as the
	    superuser.</para>
	</note>

	<para>In <xref linkend="users-modifying-chpass-su"/>, the
	  superuser has typed <command>chpass jru</command> and is
	  now viewing the fields that can be changed for this user.
	  If <systemitem class="username">jru</systemitem> runs this
	  command instead, only the last six fields will be displayed
	  and available for editing.  This is shown in
	  <xref linkend="users-modifying-chpass-ru"/>.</para>

	<example xml:id="users-modifying-chpass-su">
	  <title>Using <command>chpass</command> as
	    Superuser</title>

	  <screen>#Changing user database information for jru.
Login: jru
Password: *
Uid [#]: 1001
Gid [# or name]: 1001
Change [month day year]:
Expire [month day year]:
Class:
Home directory: /home/jru
Shell: /usr/local/bin/zsh
Full Name: J. Random User
Office Location:
Office Phone:
Home Phone:
Other information:</screen>
	</example>

	<example xml:id="users-modifying-chpass-ru">
	  <title>Using <command>chpass</command> as Regular
	    User</title>

	  <screen>#Changing user database information for jru.
Shell: /usr/local/bin/zsh
Full Name: J. Random User
Office Location:
Office Phone:
Home Phone:
Other information:</screen>
	</example>

	<note>
	  <para>The commands &man.chfn.1; and &man.chsh.1; are links
	    to &man.chpass.1;, as are &man.ypchpass.1;,
	    &man.ypchfn.1;, and &man.ypchsh.1;.  Since
	    <acronym>NIS</acronym> support is automatic, specifying
	    the <literal>yp</literal> before the command is not
	    necessary.  How to configure NIS is covered in <xref
	      linkend="network-servers"/>.</para>
	</note>
      </sect3>

      <sect3 xml:id="users-passwd">
	<title><command>passwd</command></title>

	<indexterm>
	  <primary><command>passwd</command></primary>
	</indexterm>
	<indexterm>
	  <primary>accounts</primary>
	  <secondary>changing password</secondary>
	</indexterm>

	<para>Any user can easily change their password using
	  &man.passwd.1;.  To prevent accidental or unauthorized
	  changes, this command will prompt for the user's original
	  password before a new password can be set:</para>

	<example>
	  <title>Changing Your Password</title>

	  <screen>&prompt.user; <userinput>passwd</userinput>
Changing local password for jru.
Old password:
New password:
Retype new password:
passwd: updating the database...
passwd: done</screen>
	</example>

	<para>The superuser can change any user's password by
	  specifying the username when running &man.passwd.1;.  When
	  this utility is run as the superuser, it will not prompt for
	  the user's current password.  This allows the password to be
	  changed when a user cannot remember the original
	  password.</para>

	<example>
	  <title>Changing Another User's Password as the
	    Superuser</title>

	  <screen>&prompt.root; <userinput>passwd jru</userinput>
Changing local password for jru.
New password:
Retype new password:
passwd: updating the database...
passwd: done</screen>
	</example>

	<note>
	  <para>As with &man.chpass.1;, &man.yppasswd.1; is a link to
	    &man.passwd.1;, so <acronym>NIS</acronym> works with
	    either command.</para>
	</note>
      </sect3>

      <sect3 xml:id="users-pw">
	<title><command>pw</command></title>

	<indexterm>
	  <primary><command>pw</command></primary>
	</indexterm>

	<para>The &man.pw.8; utility can create, remove,
	  modify, and display users and groups.  It functions as a
	  front end to the system user and group files.  &man.pw.8;
	  has a very powerful set of command line options that make it
	  suitable for use in shell scripts, but new users may find it
	  more complicated than the other commands presented in this
	  section.</para>
      </sect3>
    </sect2>

    <sect2 xml:id="users-groups">
      <title>Managing Groups</title>

      <indexterm>
	<primary>groups</primary>
      </indexterm>
      <indexterm>
	<primary><filename>/etc/groups</filename></primary>
      </indexterm>
      <indexterm>
	<primary>accounts</primary>
	<secondary>groups</secondary>
      </indexterm>

      <para>A group is a list of users.  A group is identified by its
	group name and <acronym>GID</acronym>.  In &os;, the kernel
	uses the <acronym>UID</acronym> of a process, and the list of
	groups it belongs to, to determine what the process is allowed
	to do.  Most of the time, the <acronym>GID</acronym> of a user
	or process usually means the first group in the list.</para>

      <para>The group name to <acronym>GID</acronym> mapping is listed
	in <filename>/etc/group</filename>.  This is a plain text file
	with four colon-delimited fields.  The first field is the
	group name, the second is the encrypted password, the third
	the <acronym>GID</acronym>, and the fourth the comma-delimited
	list of members.  For a more complete description of the
	syntax, refer to &man.group.5;.</para>

      <para>The superuser can modify <filename>/etc/group</filename>
	using a text editor.  Alternatively, &man.pw.8; can be used to
	add and edit groups.  For example, to add a group called
	<systemitem class="groupname">teamtwo</systemitem> and then
	confirm that it exists:</para>

      <example>
	<title>Adding a Group Using &man.pw.8;</title>

	<screen>&prompt.root; <userinput>pw groupadd teamtwo</userinput>
&prompt.root; <userinput>pw groupshow teamtwo</userinput>
teamtwo:*:1100:</screen>
      </example>

      <para>In this example, <literal>1100</literal> is the
	<acronym>GID</acronym> of
	<systemitem class="groupname">teamtwo</systemitem>.  Right
	now, <systemitem class="groupname">teamtwo</systemitem> has no
	members.  This command will add
	<systemitem class="username">jru</systemitem> as a member of
	<systemitem class="groupname">teamtwo</systemitem>.</para>

      <example>
	<title>Adding User Accounts to a New Group Using
	  &man.pw.8;</title>

	<screen>&prompt.root; <userinput>pw groupmod teamtwo -M jru</userinput>
&prompt.root; <userinput>pw groupshow teamtwo</userinput>
teamtwo:*:1100:jru</screen>
      </example>

      <para>The argument to <option>-M</option> is a comma-delimited
	list of users to be added to a new (empty) group or to replace
	the members of an existing group.  To the user, this group
	membership is different from (and in addition to) the user's
	primary group listed in the password file.  This means that
	the user will not show up as a member when using
	<option>groupshow</option> with &man.pw.8;, but will show up
	when the information is queried via &man.id.1; or a similar
	tool.  When &man.pw.8; is used to add a user to a group, it
	only manipulates <filename>/etc/group</filename> and does not
	attempt to read additional data from
	<filename>/etc/passwd</filename>.</para>

      <example>
	<title>Adding a New Member to a Group Using &man.pw.8;</title>

	<screen>&prompt.root; <userinput>pw groupmod teamtwo -m db</userinput>
&prompt.root; <userinput>pw groupshow teamtwo</userinput>
teamtwo:*:1100:jru,db</screen>
      </example>

      <para>In this example, the argument to <option>-m</option> is a
	comma-delimited list of users who are to be added to the
	group.  Unlike the previous example, these users are appended
	to the group and do not replace existing users in the
	group.</para>

      <example>
	<title>Using &man.id.1; to Determine Group Membership</title>

	<screen>&prompt.user; <userinput>id jru</userinput>
uid=1001(jru) gid=1001(jru) groups=1001(jru), 1100(teamtwo)</screen>
      </example>

      <para>In this example,
	<systemitem class="username">jru</systemitem> is a member of
	the groups <systemitem class="groupname">jru</systemitem> and
	<systemitem class="groupname">teamtwo</systemitem>.</para>

      <para>For more information about this command and the format of
	<filename>/etc/group</filename>, refer to &man.pw.8; and
	&man.group.5;.</para>
    </sect2>
  </sect1>

  <sect1 xml:id="permissions">
    <title>Permissions</title>

    <indexterm>
      <primary>UNIX</primary>
    </indexterm>

    <para>In &os;, every file and directory has an associated set of
      permissions and several utilities are available for viewing
      and modifying these permissions.  Understanding how permissions
      work is necessary to make sure that users are able to access
      the files that they need and are unable to improperly access
      the files used by the operating system or owned by other
      users.</para>

    <para>This section discusses the traditional &unix; permissions
      used in &os;.  For finer grained file system access control,
      refer to <xref linkend="fs-acl"/>.</para>

    <para>In &unix;, basic permissions are assigned using
      three types of access: read, write, and execute.  These access
      types are used to determine file access to the file's owner,
      group, and others (everyone else).  The read, write, and execute
      permissions can be represented as the letters
      <literal>r</literal>, <literal>w</literal>, and
      <literal>x</literal>.  They can also be represented as binary
      numbers as each permission is either on or off
      (<literal>0</literal>).  When represented as a number, the
      order is always read as <literal>rwx</literal>, where
      <literal>r</literal> has an on value of <literal>4</literal>,
      <literal>w</literal> has an on value of <literal>2</literal>
      and <literal>x</literal> has an on value of
      <literal>1</literal>.</para>

    <para>Table 4.1 summarizes the possible numeric and alphabetic
      possibilities.  When reading the <quote>Directory
	Listing</quote> column, a <literal>-</literal> is used to
      represent a permission that is set to off.</para>

    <indexterm>
      <primary>permissions</primary>
    </indexterm>
    <indexterm>
      <primary>file permissions</primary>
    </indexterm>

    <table frame="none" pgwide="1">
      <title>&unix; Permissions</title>

      <tgroup cols="3">
	<thead>
	  <row>
	    <entry>Value</entry>
	    <entry>Permission</entry>
	    <entry>Directory Listing</entry>
	  </row>
	</thead>

	<tbody>
	  <row>
	    <entry>0</entry>
	    <entry>No read, no write, no execute</entry>
	    <entry><literal>---</literal></entry>
	  </row>

	  <row>
	    <entry>1</entry>
	    <entry>No read, no write, execute</entry>
	    <entry><literal>--x</literal></entry>
	  </row>

	  <row>
	    <entry>2</entry>
	    <entry>No read, write, no execute</entry>
	    <entry><literal>-w-</literal></entry>
	  </row>

	  <row>
	    <entry>3</entry>
	    <entry>No read, write, execute</entry>
	    <entry><literal>-wx</literal></entry>
	  </row>

	  <row>
	    <entry>4</entry>
	    <entry>Read, no write, no execute</entry>
	    <entry><literal>r--</literal></entry>
	  </row>

	  <row>
	    <entry>5</entry>
	    <entry>Read, no write, execute</entry>
	    <entry><literal>r-x</literal></entry>
	  </row>

	  <row>
	    <entry>6</entry>
	    <entry>Read, write, no execute</entry>
	    <entry><literal>rw-</literal></entry>
	  </row>

	  <row>
	    <entry>7</entry>
	    <entry>Read, write, execute</entry>
	    <entry><literal>rwx</literal></entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <indexterm>
      <primary>&man.ls.1;</primary>
    </indexterm>
    <indexterm>
      <primary>directories</primary>
    </indexterm>

    <para>Use the <option>-l</option> argument to &man.ls.1; to view a
      long directory listing that includes a column of information
      about a file's permissions for the owner, group, and everyone
      else.  For example, an <command>ls -l</command> in an arbitrary
      directory may show:</para>

    <screen>&prompt.user; <userinput>ls -l</userinput>
total 530
-rw-r--r--  1 root  wheel     512 Sep  5 12:31 myfile
-rw-r--r--  1 root  wheel     512 Sep  5 12:31 otherfile
-rw-r--r--  1 root  wheel    7680 Sep  5 12:31 email.txt</screen>

    <para>The first (leftmost) character in the first column indicates
      whether this file is a regular file, a directory, a special
      character device, a socket, or any other special pseudo-file
      device.  In this example, the <literal>-</literal> indicates a
      regular file.  The next three characters, <literal>rw-</literal>
      in this example, give the permissions for the owner of the file.
      The next three characters, <literal>r--</literal>, give the
      permissions for the group that the file belongs to.  The final
      three characters, <literal>r--</literal>, give the permissions
      for the rest of the world.  A dash means that the permission is
      turned off.  In this example, the permissions are set so the
      owner can read and write to the file, the group can read the
      file, and the rest of the world can only read the file.
      According to the table above, the permissions for this file
      would be <literal>644</literal>, where each digit represents the
      three parts of the file's permission.</para>

    <para>How does the system control permissions on devices? &os;
      treats most hardware devices as a file that programs can open,
      read, and write data to.  These special device files are
      stored in <filename>/dev/</filename>.</para>

    <para>Directories are also treated as files.  They have read,
      write, and execute permissions.  The executable bit for a
      directory has a slightly different meaning than that of files.
      When a directory is marked executable, it means it is possible
      to change into that directory using &man.cd.1;.  This also
      means that it is possible to access the files within that
      directory, subject to the permissions on the files
      themselves.</para>

    <para>In order to perform a directory listing, the read permission
      must be set on the directory.  In order to delete a file that
      one knows the name of, it is necessary to have write
      <emphasis>and</emphasis> execute permissions to the directory
      containing the file.</para>

    <para>There are more permission bits, but they are primarily used
      in special circumstances such as setuid binaries and sticky
      directories.  For more information on file permissions and how
      to set them, refer to &man.chmod.1;.</para>

    <sect2>
      <info>
	<title>Symbolic Permissions</title>

	<authorgroup>
	  <author>
	    <personname>
	      <firstname>Tom</firstname>
	      <surname>Rhodes</surname>
	    </personname>
	    <contrib>Contributed by </contrib>
	  </author>
	</authorgroup>
      </info>

      <indexterm>
	<primary>permissions</primary>
	<secondary>symbolic</secondary>
      </indexterm>

      <para>Symbolic permissions use characters instead of octal
	values to assign permissions to files or directories.
	Symbolic permissions use the syntax of (who) (action)
	(permissions), where the following values are
	available:</para>

      <informaltable frame="none" pgwide="1">
	<tgroup cols="3">
	  <thead>
	    <row>
	      <entry>Option</entry>
	      <entry>Letter</entry>
	      <entry>Represents</entry>
	    </row>
	  </thead>

	  <tbody>
	    <row>
	      <entry>(who)</entry>
	      <entry>u</entry>
	      <entry>User</entry>
	    </row>

	    <row>
	      <entry>(who)</entry>
	      <entry>g</entry>
	      <entry>Group owner</entry>
	    </row>

	    <row>
	      <entry>(who)</entry>
	      <entry>o</entry>
	      <entry>Other</entry>
	    </row>

	    <row>
	      <entry>(who)</entry>
	      <entry>a</entry>
	      <entry>All (<quote>world</quote>)</entry>
	    </row>

	    <row>
	      <entry>(action)</entry>
	      <entry>+</entry>
	      <entry>Adding permissions</entry>
	    </row>

	    <row>
	      <entry>(action)</entry>
	      <entry>-</entry>
	      <entry>Removing permissions</entry>
	    </row>

	    <row>
	      <entry>(action)</entry>
	      <entry>=</entry>
	      <entry>Explicitly set permissions</entry>
	    </row>

	    <row>
	      <entry>(permissions)</entry>
	      <entry>r</entry>
	      <entry>Read</entry>
	    </row>

	    <row>
	      <entry>(permissions)</entry>
	      <entry>w</entry>
	      <entry>Write</entry>
	    </row>

	    <row>
	      <entry>(permissions)</entry>
	      <entry>x</entry>
	      <entry>Execute</entry>
	    </row>

	    <row>
	      <entry>(permissions)</entry>
	      <entry>t</entry>
	      <entry>Sticky bit</entry>
	    </row>

	    <row>
	      <entry>(permissions)</entry>
	      <entry>s</entry>
	      <entry>Set UID or GID</entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable>

      <para>These values are used with &man.chmod.1;, but with
	letters instead of numbers.  For example, the following
	command would block other users from accessing
	<replaceable>FILE</replaceable>:</para>

      <screen>&prompt.user; <userinput>chmod go= FILE</userinput></screen>

      <para>A comma separated list can be provided when more than one
	set of changes to a file must be made.  For example, the
	following command removes the group and
	<quote>world</quote> write permission on
	<replaceable>FILE</replaceable>, and adds the execute
	permissions for everyone:</para>

      <screen>&prompt.user; <userinput>chmod go-w,a+x <replaceable>FILE</replaceable></userinput></screen>

<!--
      <para>Most users will not notice this, but it should be pointed
	out that using the octal method will only set or assign
	permissions to a file; it does not add or delete them.</para>
-->
    </sect2>

    <sect2>
      <info>
	<title>&os; File Flags</title>

	<authorgroup>
	  <author>
	    <personname>
	      <firstname>Tom</firstname>
	      <surname>Rhodes</surname>
	    </personname>
	    <contrib>Contributed by </contrib>
	  </author>
	</authorgroup>
      </info>

      <para>In addition to file permissions, &os; supports the use of
	<quote>file flags</quote>.  These flags add an additional
	level of security and control over files, but not directories.
	With file flags, even
	<systemitem class="username">root</systemitem> can be
	prevented from removing or altering files.</para>

      <para>File flags are modified using &man.chflags.1;.  For
	example, to enable the system undeletable flag on the file
	<filename>file1</filename>, issue the following
	command:</para>

      <screen>&prompt.root; <userinput>chflags sunlink file1</userinput></screen>

      <para>To disable the system undeletable flag, put a
	<quote>no</quote> in front of the
	<option>sunlink</option>:</para>

      <screen>&prompt.root; <userinput>chflags nosunlink file1</userinput></screen>

      <para>To view the flags of a file, use <option>-lo</option> with
	&man.ls.1;:</para>

      <screen>&prompt.root; <userinput>ls -lo file1</userinput></screen>

      <programlisting>-rw-r--r--  1 trhodes  trhodes  sunlnk 0 Mar  1 05:54 file1</programlisting>

      <para>Several file flags may only be added or removed by the
	<systemitem class="username">root</systemitem> user.  In other
	cases, the file owner may set its file flags.  Refer to
	&man.chflags.1; and &man.chflags.2; for more
	information.</para>
    </sect2>

    <sect2>
      <info>
	<title>The <literal>setuid</literal>,
	  <literal>setgid</literal>, and <literal>sticky</literal>
	  Permissions</title>

	<authorgroup>
	  <author>
	    <personname>
	      <firstname>Tom</firstname>
	      <surname>Rhodes</surname>
	    </personname>
	    <contrib>Contributed by </contrib>
	  </author>
	</authorgroup>
      </info>

      <para>Other than the permissions already discussed, there are
	three other specific settings that all administrators should
	know about.  They are the <literal>setuid</literal>,
	<literal>setgid</literal>, and <literal>sticky</literal>
	permissions.</para>

      <para>These settings are important for some &unix; operations
	as they provide functionality not normally granted to normal
	users.  To understand them, the difference between the real
	user ID and effective user ID must be noted.</para>

      <para>The real user ID is the <acronym>UID</acronym> who owns
	or starts the process.  The effective <acronym>UID</acronym>
	is the user ID the process runs as.  As an example,
	&man.passwd.1; runs with the real user ID when a user changes
	their password.  However, in order to update the password
	database, the command runs as the effective ID of the
	<systemitem class="username">root</systemitem> user.  This
	allows users to change their passwords without seeing a
	<errorname>Permission Denied</errorname> error.</para>

      <para>The setuid permission may be set by prefixing a permission
	set with the number four (4) as shown in the following
	example:</para>

      <screen>&prompt.root; <userinput>chmod 4755 suidexample.sh</userinput></screen>

      <para>The permissions on
	<filename><replaceable>suidexample.sh</replaceable></filename>
	now look like the following:</para>

      <programlisting>-rwsr-xr-x   1 trhodes  trhodes    63 Aug 29 06:36 suidexample.sh</programlisting>

      <para>Note that a <literal>s</literal> is now part of the
	permission set designated for the file owner, replacing the
	executable bit.  This allows utilities which need elevated
	permissions, such as &man.passwd.1;.</para>

      <note>
	<para>The <literal>nosuid</literal> &man.mount.8; option will
	  cause such binaries to silently fail without alerting
	  the user.  That option is not completely reliable as a
	  <literal>nosuid</literal> wrapper may be able to circumvent
	  it.</para>
      </note>

      <para>To view this in real time, open two terminals.  On
	one, type <command>passwd</command> as a normal user.
	While it waits for a new password, check the process
	table and look at the user information for
	&man.passwd.1;:</para>

      <para>In terminal A:</para>

      <screen>Changing local password for trhodes
Old Password:</screen>

      <para>In terminal B:</para>

      <screen>&prompt.root; <userinput>ps aux | grep passwd</userinput></screen>

      <screen>trhodes  5232  0.0  0.2  3420  1608   0  R+    2:10AM   0:00.00 grep passwd
root     5211  0.0  0.2  3620  1724   2  I+    2:09AM   0:00.01 passwd</screen>

      <para>Although &man.passwd.1; is run as a normal user, it is
	using the effective <acronym>UID</acronym> of
	<systemitem class="username">root</systemitem>.</para>

      <para>The <literal>setgid</literal> permission performs the
	same function as the <literal>setuid</literal> permission;
	except that it alters the group settings.  When an application
	or utility executes with this setting, it will be granted the
	permissions based on the group that owns the file, not the
	user who started the process.</para>

      <para>To set the <literal>setgid</literal> permission on a
	file, provide &man.chmod.1; with a leading two (2):</para>

      <screen>&prompt.root; <userinput>chmod 2755 sgidexample.sh</userinput></screen>

      <para>In the following listing, notice that the
	<literal>s</literal> is now in the field designated for the
	group permission settings:</para>

      <screen>-rwxr-sr-x   1 trhodes  trhodes    44 Aug 31 01:49 sgidexample.sh</screen>

      <note>
	<para>In these examples, even though the shell script in
	  question is an executable file, it will not run with
	  a different <acronym>EUID</acronym> or effective user ID.
	  This is because shell scripts may not access the
	  &man.setuid.2; system calls.</para>
      </note>

      <para>The <literal>setuid</literal> and
	<literal>setgid</literal> permission bits may lower system
	security, by allowing for elevated permissions.  The third
	special permission, the <literal>sticky bit</literal>, can
	strengthen the security of a system.</para>

      <para>When the <literal>sticky bit</literal> is set on a
	directory, it allows file deletion only by the file owner.
	This is useful to prevent file deletion in public directories,
	such as <filename>/tmp</filename>, by users
	who do not own the file.  To utilize this permission, prefix
	the permission set with a one (1):</para>

      <screen>&prompt.root; <userinput>chmod 1777 /tmp</userinput></screen>

      <para>The <literal>sticky bit</literal> permission will display
	as a <literal>t</literal> at the very end of the permission
	set:</para>

      <screen>&prompt.root; <userinput>ls -al / | grep tmp</userinput></screen>

      <screen>drwxrwxrwt  10 root  wheel         512 Aug 31 01:49 tmp</screen>

    </sect2>
  </sect1>

  <sect1 xml:id="dirstructure">
    <title>Directory Structure</title>

    <indexterm>
      <primary>directory hierarchy</primary>
    </indexterm>

    <para>The &os; directory hierarchy is fundamental to obtaining
      an overall understanding of the system.  The most important
      directory is root or, <quote>/</quote>.  This directory is the
      first one mounted at boot time and it contains the base system
      necessary to prepare the operating system for multi-user
      operation.  The root directory also contains mount points for
      other file systems that are mounted during the transition to
      multi-user operation.</para>

    <para>A mount point is a directory where additional file systems
      can be grafted onto a parent file system (usually the root file
      system).  This is further described in
      <xref linkend="disk-organization"/>.  Standard mount points
      include <filename>/usr/</filename>, <filename>/var/</filename>,
      <filename>/tmp/</filename>, <filename>/mnt/</filename>, and
      <filename>/cdrom/</filename>.  These directories are usually
      referenced to entries in <filename>/etc/fstab</filename>.  This
      file is a table of various file systems and mount points and is
      read by the system.  Most of the file systems in
      <filename>/etc/fstab</filename> are mounted automatically at
      boot time from the script &man.rc.8; unless their entry includes
      <option>noauto</option>.  Details can be found in
      <xref linkend="disks-fstab"/>.</para>

    <para>A complete description of the file system hierarchy is
      available in &man.hier.7;.  The following table provides a brief
      overview of the most common directories.</para>

    <para>
      <informaltable frame="none" pgwide="1">
	<tgroup cols="2">
	  <thead>
	    <row>
	      <entry>Directory</entry>
	      <entry>Description</entry>
	    </row>
	  </thead>
	  <tbody valign="top">
	    <row>
	      <entry><filename>/</filename></entry>
	      <entry>Root directory of the file system.</entry>
	    </row>

	    <row>
	      <entry><filename>/bin/</filename></entry>
	      <entry>User utilities fundamental to both single-user
		and multi-user environments.</entry>
	    </row>

	    <row>
	      <entry><filename>/boot/</filename></entry>
	      <entry>Programs and configuration files used during
		operating system bootstrap.</entry>
	    </row>

	    <row>
	      <entry><filename>/boot/defaults/</filename></entry>
	      <entry>Default boot configuration files.  Refer to
		&man.loader.conf.5; for details.</entry>
	    </row>

	    <row>
	      <entry><filename>/dev/</filename></entry>
	      <entry>Device nodes.  Refer to &man.intro.4; for
		details.</entry>
	    </row>

	    <row>
	      <entry><filename>/etc/</filename></entry>
	      <entry>System configuration files and scripts.</entry>
	    </row>

	    <row>
	      <entry><filename>/etc/defaults/</filename></entry>
	      <entry>Default system configuration files.  Refer to
		&man.rc.8; for details.</entry>
	    </row>

	    <row>
	      <entry><filename>/etc/mail/</filename></entry>
	      <entry>Configuration files for mail transport agents
		such as &man.sendmail.8;.</entry>
	    </row>

	    <row>
	      <entry><filename>/etc/periodic/</filename></entry>
	      <entry>Scripts that run daily, weekly, and monthly,
		via &man.cron.8;.  Refer to &man.periodic.8; for
		details.</entry>
	    </row>

	    <row>
	      <entry><filename>/etc/ppp/</filename></entry>
	      <entry>&man.ppp.8; configuration files.</entry>
	    </row>

	    <row>
	      <entry><filename>/mnt/</filename></entry>
	      <entry>Empty directory commonly used by system
		administrators as a temporary mount point.</entry>
	    </row>

	    <row>
	      <entry><filename>/proc/</filename></entry>
	      <entry>Process file system.  Refer to &man.procfs.5;,
		&man.mount.procfs.8; for details.</entry>
	    </row>

	    <row>
	      <entry><filename>/rescue/</filename></entry>
	      <entry>Statically linked programs for emergency
		recovery as described in &man.rescue.8;.</entry>
	    </row>

	    <row>
	      <entry><filename>/root/</filename></entry>
	      <entry>Home directory for the
		<systemitem class="username">root</systemitem>
		account.</entry>
	    </row>

	    <row>
	      <entry><filename>/sbin/</filename></entry>
	      <entry>System programs and administration utilities
		fundamental to both single-user and multi-user
		environments.</entry>
	    </row>

	    <row>
	      <entry><filename>/tmp/</filename></entry>
	      <entry>Temporary files which are usually
		<emphasis>not</emphasis> preserved across a system
		reboot.  A memory-based file system is often mounted
		at <filename>/tmp</filename>.  This can be automated
		using the tmpmfs-related variables of &man.rc.conf.5;
		or with an entry in <filename>/etc/fstab</filename>;
		refer to &man.mdmfs.8; for details.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/</filename></entry>
	      <entry>The majority of user utilities and
		applications.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/bin/</filename></entry>
	      <entry>Common utilities, programming tools, and
		applications.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/include/</filename></entry>
	      <entry>Standard C include files.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/lib/</filename></entry>
	      <entry>Archive libraries.</entry>
	    </row>


	    <row>
	      <entry><filename>/usr/libdata/</filename></entry>
	      <entry>Miscellaneous utility data files.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/libexec/</filename></entry>
	      <entry>System daemons and system utilities executed
		by other programs.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/local/</filename></entry>
	      <entry>Local executables and libraries.  Also used as
		the default destination for the &os; ports framework.
		Within
		<filename>/usr/local</filename>, the
		general layout sketched out by &man.hier.7; for
		<filename>/usr</filename> should be
		used.  Exceptions are the man directory, which is
		directly under <filename
		  >/usr/local</filename> rather than
		under <filename
		  >/usr/local/share</filename>, and
		the ports documentation is in <filename
		  >share/doc/<replaceable>port</replaceable></filename>.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/obj/</filename></entry>
	      <entry>Architecture-specific target tree produced by
		building the <filename>/usr/src</filename>
		tree.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/ports/</filename></entry>
	      <entry>The &os; Ports Collection (optional).</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/sbin/</filename></entry>
	      <entry>System daemons and system utilities executed
		by users.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/share/</filename></entry>
	      <entry>Architecture-independent files.</entry>
	    </row>

	    <row>
	      <entry><filename>/usr/src/</filename></entry>
	      <entry>BSD and/or local source files.</entry>
	    </row>

	    <row>
	      <entry><filename>/var/</filename></entry>
	      <entry>Multi-purpose log, temporary, transient, and
		spool files.  A memory-based file system is sometimes
		mounted at
		<filename>/var</filename>.  This can
		be automated using the varmfs-related variables in
		&man.rc.conf.5; or with an entry in
		<filename>/etc/fstab</filename>; refer to
		&man.mdmfs.8; for details.</entry>
	    </row>

	    <row>
	      <entry><filename>/var/log/</filename></entry>
	      <entry>Miscellaneous system log files.</entry>
	    </row>

	    <row>
	      <entry><filename>/var/mail/</filename></entry>
	      <entry>User mailbox files.</entry>
	    </row>

	    <row>
	      <entry><filename>/var/spool/</filename></entry>
	      <entry>Miscellaneous printer and mail system spooling
		directories.</entry>
	    </row>

	    <row>
	      <entry><filename>/var/tmp/</filename></entry>
	      <entry>Temporary files which are usually preserved
		across a system reboot, unless
		<filename>/var</filename> is a
		memory-based file system.</entry>
	    </row>

	    <row>
	      <entry><filename>/var/yp/</filename></entry>
	      <entry>NIS maps.</entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable></para>
  </sect1>

  <sect1 xml:id="disk-organization">
    <title>Disk Organization</title>

    <para>The smallest unit of organization that &os; uses to find
      files is the filename.  Filenames are case-sensitive, which
      means that <filename>readme.txt</filename> and
      <filename>README.TXT</filename> are two separate files.  &os;
      does not use the extension of a file to determine whether the
      file is a program, document, or some other form of data.</para>

    <para>Files are stored in directories.  A directory may contain no
      files, or it may contain many hundreds of files.  A directory
      can also contain other directories, allowing a hierarchy of
      directories within one another in order to organize
      data.</para>

    <para>Files and directories are referenced by giving the file or
      directory name, followed by a forward slash,
      <literal>/</literal>, followed by any other directory names that
      are necessary.  For example, if the directory
      <filename>foo</filename> contains a directory
      <filename>bar</filename> which contains the
      file <filename>readme.txt</filename>, the full name, or
      <firstterm>path</firstterm>, to the file is
      <filename>foo/bar/readme.txt</filename>.  Note that this is
      different from &windows; which uses <literal>\</literal> to
      separate file and directory names.  &os; does not use drive
      letters, or other drive names in the path.  For example, one
      would not type <filename>c:\foo\bar\readme.txt</filename> on
      &os;.</para>

    <para>Directories and files are stored in a file system.  Each
      file system contains exactly one directory at the very top
      level, called the <firstterm>root directory</firstterm> for that
      file system.  This root directory can contain other directories.
      One file system is designated the
      <firstterm>root file system</firstterm> or <literal>/</literal>.
      Every other file system is <firstterm>mounted</firstterm> under
      the root file system.  No matter how many disks are on the &os;
      system, every directory appears to be part of the same
      disk.</para>

    <para>Consider three file systems, called <literal>A</literal>,
      <literal>B</literal>, and <literal>C</literal>.  Each file
      system has one root directory, which contains two other
      directories, called <literal>A1</literal>, <literal>A2</literal>
      (and likewise <literal>B1</literal>, <literal>B2</literal> and
      <literal>C1</literal>, <literal>C2</literal>).</para>

    <para>Call <literal>A</literal> the root file system.  If
      &man.ls.1; is used to view the contents of this directory,
      it will show two subdirectories, <literal>A1</literal> and
      <literal>A2</literal>.  The directory tree looks like
      this:</para>

    <mediaobject>
      <imageobject>
	<imagedata fileref="basics/example-dir1"/>
      </imageobject>

      <textobject>
	<literallayout class="monospaced"> /
 |
 +--- A1
 |
 `--- A2</literallayout>
      </textobject>
    </mediaobject>

    <para>A file system must be mounted on to a directory in another
      file system.  When mounting file system <literal>B</literal>
      on to the directory <literal>A1</literal>, the root directory
      of <literal>B</literal> replaces <literal>A1</literal>, and
      the directories in <literal>B</literal> appear
      accordingly:</para>

    <mediaobject>
      <imageobject>
	<imagedata fileref="basics/example-dir2"/>
      </imageobject>

      <textobject>
	<literallayout class="monospaced"> /
 |
 +--- A1
 |     |
 |     +--- B1
 |     |
 |     `--- B2
 |
 `--- A2</literallayout>
      </textobject>
    </mediaobject>

    <para>Any files that are in the <literal>B1</literal> or
      <literal>B2</literal> directories can be reached with the path
      <filename>/A1/B1</filename> or
      <filename>/A1/B2</filename> as necessary.  Any
      files that were in <filename>/A1</filename>
      have been temporarily hidden.  They will reappear if
      <literal>B</literal> is <firstterm>unmounted</firstterm> from
      <literal>A</literal>.</para>

    <para>If <literal>B</literal> had been mounted on
      <literal>A2</literal> then the diagram would look like
      this:</para>

    <mediaobject>
      <imageobject>
	<imagedata fileref="basics/example-dir3"/>
      </imageobject>

      <textobject>
	<literallayout class="monospaced"> /
 |
 +--- A1
 |
 `--- A2
       |
       +--- B1
       |
       `--- B2</literallayout>
      </textobject>
    </mediaobject>

    <para>and the paths would be
      <filename>/A2/B1</filename> and
      <filename>/A2/B2</filename>
      respectively.</para>

    <para>File systems can be mounted on top of one another.
      Continuing the last example, the <literal>C</literal> file
      system could be mounted on top of the <literal>B1</literal>
      directory in the <literal>B</literal> file system, leading to
      this arrangement:</para>

    <mediaobject>
      <imageobject>
	<imagedata fileref="basics/example-dir4"/>
      </imageobject>

      <textobject>
	<literallayout class="monospaced"> /
 |
 +--- A1
 |
 `--- A2
       |
       +--- B1
       |     |
       |     +--- C1
       |     |
       |     `--- C2
       |
       `--- B2</literallayout>
      </textobject>
    </mediaobject>

    <para>Or <literal>C</literal> could be mounted directly on to the
      <literal>A</literal> file system, under the
      <literal>A1</literal> directory:</para>

    <mediaobject>
      <imageobject>
	<imagedata fileref="basics/example-dir5"/>
      </imageobject>

      <textobject>
	<literallayout class="monospaced"> /
 |
 +--- A1
 |     |
 |     +--- C1
 |     |
 |     `--- C2
 |
 `--- A2
       |
       +--- B1
       |
       `--- B2</literallayout>
      </textobject>
    </mediaobject>

    <para>It is entirely possible to have one large root file system,
      and not need to create any others.  There are some drawbacks to
      this approach, and one advantage.</para>

    <itemizedlist>
      <title>Benefits of Multiple File Systems</title>

      <listitem>
	<para>Different file systems can have different
	  <firstterm>mount options</firstterm>.  For example, the root
	  file system can be mounted read-only, making it impossible
	  for users to inadvertently delete or edit a critical file.
	  Separating user-writable file systems, such as
	  <filename>/home</filename>, from other
	  file systems allows them to be mounted
	  <firstterm>nosuid</firstterm>.  This option prevents the
	  <firstterm>suid</firstterm>/<firstterm>guid</firstterm> bits
	  on executables stored on the file system from taking effect,
	  possibly improving security.</para>
      </listitem>

      <listitem>
	<para>&os; automatically optimizes the layout of files on a
	  file system, depending on how the file system is being used.
	  So a file system that contains many small files that are
	  written frequently will have a different optimization to one
	  that contains fewer, larger files.  By having one big file
	  system this optimization breaks down.</para>
      </listitem>

      <listitem>
	<para>&os;'s file systems are robust if power is lost.
	  However, a power loss at a critical point could still damage
	  the structure of the file system.  By splitting data over
	  multiple file systems it is more likely that the system will
	  still come up, making it easier to restore from backup as
	  necessary.</para>
      </listitem>
    </itemizedlist>

    <itemizedlist>
      <title>Benefit of a Single File System</title>

      <listitem>
	<para>File systems are a fixed size.  If you create a file
	  system when you install &os; and give it a specific size,
	  you may later discover that you need to make the partition
	  bigger.  This is not easily accomplished without backing up,
	  recreating the file system with the new size, and then
	  restoring the backed up data.</para>

	<important>
	  <para>&os; features the &man.growfs.8; command, which makes
	    it possible to increase the size of file system on the
	    fly, removing this limitation.</para>
	</important>
      </listitem>
    </itemizedlist>

    <para>File systems are contained in partitions.  This does not
      have the same meaning as the common usage of the term partition
      (for example, &ms-dos; partition), because of &os;'s &unix;
      heritage.  Each partition is identified by a letter from
      <literal>a</literal> through to <literal>h</literal>.  Each
      partition can contain only one file system, which means that
      file systems are often described by either their typical mount
      point in the file system hierarchy, or the letter of the
      partition they are contained in.</para>

    <para>&os; also uses disk space for
      <firstterm>swap space</firstterm> to provide
      <firstterm>virtual memory</firstterm>.  This allows your
      computer to behave as though it has much more memory than it
      actually does.  When &os; runs out of memory, it moves some of
      the data that is not currently being used to the swap space, and
      moves it back in (moving something else out) when it needs
      it.</para>

    <para>Some partitions have certain conventions associated with
      them.</para>

    <informaltable frame="none" pgwide="1">
      <tgroup cols="2">
	<colspec colwidth="1*"/>
	<colspec colwidth="5*"/>

	<thead>
	  <row>
	    <entry>Partition</entry>
	    <entry>Convention</entry>
	  </row>
	</thead>

	<tbody valign="top">
	  <row>
	    <entry><literal>a</literal></entry>
	    <entry>Normally contains the root file system.</entry>
	  </row>

	  <row>
	    <entry><literal>b</literal></entry>
	    <entry>Normally contains swap space.</entry>
	  </row>

	  <row>
	    <entry><literal>c</literal></entry>
	    <entry>Normally the same size as the enclosing slice.
	      This allows utilities that need to work on the entire
	      slice, such as a bad block scanner, to work on the
	      <literal>c</literal> partition.  A file system would not
	      normally be created on this partition.</entry>
	  </row>

	  <row>
	    <entry><literal>d</literal></entry>
	    <entry>Partition <literal>d</literal> used to have a
	      special meaning associated with it, although that is now
	      gone and <literal>d</literal> may work as any normal
	      partition.</entry>
	  </row>
	</tbody>
      </tgroup>
    </informaltable>

    <para>Disks in &os; are divided into slices, referred to in
      &windows; as partitions, which are numbered from 1 to 4.  These
      are then divided into partitions, which contain file systems,
      and are labeled using letters.</para>

    <indexterm>
      <primary>slices</primary>
    </indexterm>
    <indexterm>
      <primary>partitions</primary>
    </indexterm>
    <indexterm>
      <primary>dangerously dedicated</primary>
    </indexterm>

    <para>Slice numbers follow the device name, prefixed with an
      <literal>s</literal>, starting at 1.  So
      <quote>da0<emphasis>s1</emphasis></quote> is the first slice on
      the first SCSI drive.  There can only be four physical slices on
      a disk, but there can be logical slices inside physical slices
      of the appropriate type.  These extended slices are numbered
      starting at 5, so <quote>ada0<emphasis>s5</emphasis></quote> is
      the first extended slice on the first SATA disk.  These devices
      are used by file systems that expect to occupy a slice.</para>

    <para>Slices, <quote>dangerously dedicated</quote> physical
      drives, and other drives contain
      <firstterm>partitions</firstterm>, which are represented as
      letters from <literal>a</literal> to <literal>h</literal>.  This
      letter is appended to the device name, so
      <quote>da0<emphasis>a</emphasis></quote> is the
      <literal>a</literal> partition on the first
      <literal>da</literal> drive, which is
      <quote>dangerously dedicated</quote>.
      <quote>ada1s3<emphasis>e</emphasis></quote> is the fifth
      partition in the third slice of the second SATA disk
      drive.</para>

    <para>Finally, each disk on the system is identified.  A disk name
      starts with a code that indicates the type of disk, and then a
      number, indicating which disk it is.  Unlike slices, disk
      numbering starts at 0.  Common codes are listed in
      <xref linkend="disks-naming"/>.</para>

    <para>When referring to a partition, include the disk name,
      <literal>s</literal>, the slice number, and then the partition
      letter.  Examples are shown in
      <xref linkend="basics-disk-slice-part"/>.</para>

    <para><xref linkend="basics-concept-disk-model"/> shows a
      conceptual model of a disk layout.</para>

    <para>When installing &os;, configure the disk slices, create
      partitions within the slice to be used for &os;, create a file
      system or swap space in each partition, and decide where each
      file system will be mounted.</para>

    <table frame="none" pgwide="1" xml:id="disks-naming">
      <title>Disk Device Names</title>

      <tgroup cols="2">
	<colspec colwidth="1*"/>
	<colspec colwidth="5*"/>

	<thead>
	  <row>
	    <entry>Drive Type</entry>
	    <entry>Drive Device Name</entry>
	  </row>
	</thead>

	<tbody>
	  <row>
	    <entry><acronym>SATA</acronym> and <acronym>IDE</acronym>
	      hard drives</entry>
	    <entry><literal>ada</literal> or
	      <literal>ad</literal></entry>
	  </row>

	  <row>
	    <entry><acronym>SCSI</acronym> hard drives and
	      <acronym>USB</acronym> storage devices</entry>
	    <entry><literal>da</literal></entry>
	  </row>

	  <row>
	    <entry><acronym>SATA</acronym> and <acronym>IDE</acronym>
	      <acronym>CD-ROM</acronym> drives</entry>
	    <entry><literal>cd</literal> or
	      <literal>acd</literal></entry>
	  </row>

	  <row>
	    <entry><acronym>SCSI</acronym> <acronym>CD-ROM</acronym>
	      drives</entry>
	    <entry><literal>cd</literal></entry>
	  </row>

	  <row>
	    <entry>Floppy drives</entry>
	    <entry><literal>fd</literal></entry>
	  </row>

	  <row>
	    <entry>Assorted non-standard <acronym>CD-ROM</acronym>
	      drives</entry>
	    <entry><literal>mcd</literal> for Mitsumi
	      <acronym>CD-ROM</acronym> and <literal>scd</literal> for
	      Sony <acronym>CD-ROM</acronym> devices</entry>
	  </row>

	  <row>
	    <entry><acronym>SCSI</acronym> tape drives</entry>
	    <entry><literal>sa</literal></entry>
	  </row>

	  <row>
	    <entry><acronym>IDE</acronym> tape drives</entry>
	    <entry><literal>ast</literal></entry>
	  </row>

	  <row>
	    <entry>RAID drives</entry>
	    <entry>Examples include <literal>aacd</literal> for
	      &adaptec; AdvancedRAID, <literal>mlxd</literal> and
	      <literal>mlyd</literal> for &mylex;,
	      <literal>amrd</literal> for AMI &megaraid;,
	      <literal>idad</literal> for Compaq Smart RAID,
	      <literal>twed</literal> for &tm.3ware; RAID.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <example xml:id="basics-disk-slice-part">
      <title>Sample Disk, Slice, and Partition Names</title>

      <informaltable frame="none" pgwide="1">
	<tgroup cols="2">
	  <colspec colwidth="1*"/>
	  <colspec colwidth="5*"/>

	  <thead>
	    <row>
	      <entry>Name</entry>
	      <entry>Meaning</entry>
	    </row>
	  </thead>

	  <tbody>
	    <row>
	      <entry><literal>ada0s1a</literal></entry>
	      <entry>The first partition (<literal>a</literal>) on the
		first slice (<literal>s1</literal>) on the first
		<acronym>SATA</acronym>
		disk (<literal>ada0</literal>).</entry>
	    </row>

	    <row>
	      <entry><literal>da1s2e</literal></entry>
	      <entry>The fifth partition (<literal>e</literal>) on the
		second slice (<literal>s2</literal>) on the second
		SCSI disk (<literal>da1</literal>).</entry>
	    </row>
	  </tbody>
	</tgroup>
      </informaltable>
    </example>

    <example xml:id="basics-concept-disk-model">
      <title>Conceptual Model of a Disk</title>

      <para>This diagram shows &os;'s view of the first
	<acronym>SATA</acronym> disk attached to the system.  Assume
	that the disk is 250&nbsp;GB in size, and contains an
	80&nbsp;GB slice and a 170&nbsp;GB slice (&ms-dos;
	partitions).  The first slice contains a &windows;
	<acronym>NTFS</acronym> file system, <filename>C:</filename>,
	and the second slice contains a &os; installation.  This
	example &os; installation has four data partitions and a swap
	partition.</para>

      <para>The four partitions each hold a file system.  Partition
	<literal>a</literal> is used for the root file system,
	<literal>d</literal> for <filename>/var/</filename>,
	<literal>e</literal> for <filename>/tmp/</filename>, and
	<literal>f</literal> for <filename>/usr/</filename>.
	Partition letter <literal>c</literal> refers to the entire
	slice, and so is not used for ordinary partitions.</para>

      <mediaobject>
	<imageobject>
	  <imagedata fileref="basics/disk-layout"/>
	</imageobject>
      </mediaobject>
    </example>
  </sect1>

  <sect1 xml:id="mount-unmount">
    <title>Mounting and Unmounting File Systems</title>

    <para>The file system is best visualized as a tree, rooted, as it
      were, at <filename>/</filename>.
      <filename>/dev</filename>,
      <filename>/usr</filename>, and the other
      directories in the root directory are branches, which may have
      their own branches, such as
      <filename>/usr/local</filename>, and so
      on.</para>

    <indexterm>
      <primary>root file system</primary>
    </indexterm>

    <para>There are various reasons to house some of these
      directories on separate file systems.
      <filename>/var</filename> contains the
      directories <filename>log/</filename>,
      <filename>spool/</filename>, and various types
      of temporary files, and as such, may get filled up.  Filling up
      the root file system is not a good idea, so splitting
      <filename>/var</filename> from
      <filename>/</filename> is often
      favorable.</para>

    <para>Another common reason to contain certain directory trees on
      other file systems is if they are to be housed on separate
      physical disks, or are separate virtual disks, such as Network
      File System mounts, described in <xref linkend="network-nfs"/>,
      or CDROM drives.</para>

    <sect2 xml:id="disks-fstab">
      <title>The <filename>fstab</filename> File</title>

      <indexterm>
	<primary>file systems</primary>
	<secondary>mounted with fstab</secondary>
      </indexterm>

      <para>During the boot process (<xref linkend="boot"/>), file
	systems listed in <filename>/etc/fstab</filename> are
	automatically mounted except for the entries containing
	<option>noauto</option>.  This file contains entries in the
	following format:</para>

      <programlisting><replaceable>device</replaceable>       <replaceable>/mount-point</replaceable> <replaceable>fstype</replaceable>     <replaceable>options</replaceable>      <replaceable>dumpfreq</replaceable>     <replaceable>passno</replaceable></programlisting>

      <variablelist>
	<varlistentry>
	  <term><literal>device</literal></term>
	  <listitem>
	    <para>An existing device name as explained in
	      <xref linkend="disks-naming"/>.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><literal>mount-point</literal></term>

	  <listitem>
	    <para>An existing directory on which to mount the file
	      system.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><literal>fstype</literal></term>

	  <listitem>
	    <para>The file system type to pass to &man.mount.8;.  The
	      default &os; file system is
	      <literal>ufs</literal>.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><literal>options</literal></term>

	  <listitem>
	    <para>Either <option>rw</option> for read-write file
	      systems, or <option>ro</option> for read-only file
	      systems, followed by any other options that may be
	      needed.  A common option is <option>noauto</option> for
	      file systems not normally mounted during the boot
	      sequence.  Other options are listed in
	      &man.mount.8;.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><literal>dumpfreq</literal></term>

	  <listitem>
	    <para>Used by &man.dump.8; to determine which file systems
	      require dumping.  If the field is missing, a value of
	      zero is assumed.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><literal>passno</literal></term>

	  <listitem>
	    <para>Determines the order in which file systems should be
	      checked.  File systems that should be skipped should
	      have their <literal>passno</literal> set to zero.  The
	      root file system needs to be checked before everything
	      else and should have its <literal>passno</literal> set
	      to one.  The other file systems should be set to
	      values greater than one.  If more than one file system
	      has the same <literal>passno</literal>, &man.fsck.8;
	      will attempt to check file systems in parallel if
	      possible.</para>
	  </listitem>
	</varlistentry>
      </variablelist>

      <para>Refer to &man.fstab.5; for more information on the format
	of <filename>/etc/fstab</filename> and its options.</para>
    </sect2>

    <sect2 xml:id="disks-mount">
      <title>Using &man.mount.8;</title>

      <indexterm>
	<primary>file systems</primary>
	<secondary>mounting</secondary>
      </indexterm>

      <para>File systems are mounted using &man.mount.8;.  The most
	basic syntax is as follows:</para>

      <informalexample>
	<screen>&prompt.root; <userinput>mount <replaceable>device</replaceable> <replaceable>mountpoint</replaceable></userinput></screen>
      </informalexample>

      <para>This command provides many options which are described in
	&man.mount.8;, The most commonly used options include:</para>

      <variablelist>
	<title>Mount Options</title>

	<varlistentry>
	  <term><option>-a</option></term>

	  <listitem>
	    <para>Mount all the file systems listed in
	      <filename>/etc/fstab</filename>, except those marked as
	      <quote>noauto</quote>, excluded by the
	      <option>-t</option> flag, or those that are already
	      mounted.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-d</option></term>

	  <listitem>

	    <para>Do everything except for the actual mount system
	      call.  This option is useful in conjunction with the
	      <option>-v</option> flag to determine what &man.mount.8;
	      is actually trying to do.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-f</option></term>

	  <listitem>
	    <para>Force the mount of an unclean file system
	      (dangerous), or the revocation of write access when
	      downgrading a file system's mount status from read-write
	      to read-only.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-r</option></term>

	  <listitem>
	    <para>Mount the file system read-only.  This is identical
	      to using <option>-o ro</option>.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-t</option>
	    <replaceable>fstype</replaceable></term>

	  <listitem>
	    <para>Mount the specified file system type or mount only
	      file systems of the given type, if <option>-a</option>
	      is included.  <quote>ufs</quote> is the default file
	      system type.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-u</option></term>

	  <listitem>
	    <para>Update mount options on the file system.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-v</option></term>

	  <listitem>
	    <para>Be verbose.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-w</option></term>

	  <listitem>
	    <para>Mount the file system read-write.</para>
	  </listitem>
	</varlistentry>
      </variablelist>

      <para>The following options can be passed to <option>-o</option>
	as a comma-separated list:</para>

      <variablelist>
	<varlistentry>
	  <term>nosuid</term>

	  <listitem>
	    <para>Do not interpret setuid or setgid flags on the
	      file system.  This is also a useful security
	      option.</para>
	  </listitem>
	</varlistentry>
      </variablelist>
    </sect2>

    <sect2 xml:id="disks-umount">
      <title>Using &man.umount.8;</title>

      <indexterm>
	<primary>file systems</primary>
	<secondary>unmounting</secondary>
      </indexterm>

      <para>To unmount a file system use &man.umount.8;.  This command
	takes one parameter which can be a mountpoint, device name,
	<option>-a</option> or <option>-A</option>.</para>

      <para>All forms take <option>-f</option> to force unmounting,
	and <option>-v</option> for verbosity.  Be warned that
	<option>-f</option> is not generally a good idea as it might
	crash the computer or damage data on the file system.</para>

      <para>To unmount all mounted file systems, or just the file
	system types listed after <option>-t</option>, use
	<option>-a</option> or <option>-A</option>.  Note that
	<option>-A</option> does not attempt to unmount the root file
	system.</para>
    </sect2>
  </sect1>

  <sect1 xml:id="basics-processes">
    <title>Processes and Daemons</title>

    <para>&os; is a multi-tasking operating system.  Each program
      running at any one time is called a
      <firstterm>process</firstterm>.  Every running command starts
      at least one new process and there are a number of system
      processes that are run by &os;.</para>

    <para>Each process is uniquely identified by a number called a
      <firstterm>process ID</firstterm> (<acronym>PID</acronym>).
      Similar to files, each process has one owner and group, and
      the owner and group permissions are used to determine which
      files and devices the process can open.  Most processes also
      have a parent process that started them.  For example, the
      shell is a process, and any command started in the shell is a
      process which has the shell as its parent process.  The
      exception is a special process called &man.init.8; which is
      always the first process to start at boot time and which always
      has a <acronym>PID</acronym> of <literal>1</literal>.</para>

    <para>Some programs are not designed to be run with continuous
      user input and disconnect from the terminal at the first
      opportunity.  For example, a web server responds to web
      requests, rather than user input.  Mail servers are another
      example of this type of application.  These types of programs
      are known as <firstterm>daemons</firstterm>.  The term daemon
      comes from Greek mythology and represents an entity that is
      neither good nor evil, and which invisibly performs useful
      tasks.  This is why the BSD mascot is the cheerful-looking
      daemon with sneakers and a pitchfork.</para>

    <para>There is a convention to name programs that normally run as
      daemons with a trailing <quote>d</quote>.  For example,
      <application>BIND</application> is the Berkeley Internet Name
      Domain, but the actual program that executes is
      <command>named</command>.  The
      <application>Apache</application> web server program is
      <command>httpd</command> and the line printer spooling daemon
      is <command>lpd</command>.  This is only a naming convention.
      For example, the main mail daemon for the
      <application>Sendmail</application> application is
      <command>sendmail</command>, and not
      <literal>maild</literal>.</para>

    <sect2>
      <title>Viewing Processes</title>

      <para>To see the processes running on the system, use &man.ps.1;
	or &man.top.1;.   To display a static list of the currently
	running processes, their <acronym>PID</acronym>s, how much
	memory they are using, and the command they were started with,
	use &man.ps.1;.  To display all the running processes and
	update the display every few seconds in order to interactively
	see what the computer is doing, use &man.top.1;.</para>

      <para>By default, &man.ps.1; only shows the commands that are
	running and owned by the user.  For example:</para>

      <screen>&prompt.user; <userinput>ps</userinput>
 PID TT  STAT    TIME COMMAND
8203  0  Ss   0:00.59 /bin/csh
8895  0  R+   0:00.00 ps</screen>

      <para>The output from &man.ps.1; is organized into a number of
	columns.  The <literal>PID</literal> column displays the
	process ID.  <acronym>PID</acronym>s are assigned starting at
	1, go up to 99999, then wrap around back to the beginning.
	However, a <acronym>PID</acronym> is not reassigned if it is
	already in use.  The <literal>TT</literal> column shows the
	tty the program is running on and <literal>STAT</literal>
	shows the program's state.  <literal>TIME</literal> is the
	amount of time the program has been running on the CPU.  This
	is usually not the elapsed time since the program was started,
	as most programs spend a lot of time waiting for things to
	happen before they need to spend time on the CPU.  Finally,
	<literal>COMMAND</literal> is the command that was used to
	start the program.</para>

      <para>A number of different options are available to change the
	information that is displayed.  One of the most useful sets is
	<literal>auxww</literal>, where  <option>a</option> displays
	information about all the running processes of all users,
	<option>u</option> displays the username and memory usage of
	the process' owner, <option>x</option> displays
	information about daemon processes, and <option>ww</option>
	causes &man.ps.1; to display the full command line for each
	process, rather than truncating it once it gets too long to
	fit on the screen.</para>

      <para>The output from &man.top.1; is similar:</para>

      <screen>&prompt.user; <userinput>top</userinput>
last pid:  9609;  load averages:  0.56,  0.45,  0.36              up 0+00:20:03  10:21:46
107 processes: 2 running, 104 sleeping, 1 zombie
CPU:  6.2% user,  0.1% nice,  8.2% system,  0.4% interrupt, 85.1% idle
Mem: 541M Active, 450M Inact, 1333M Wired, 4064K Cache, 1498M Free
ARC: 992M Total, 377M MFU, 589M MRU, 250K Anon, 5280K Header, 21M Other
Swap: 2048M Total, 2048M Free

  PID USERNAME    THR PRI NICE   SIZE    RES STATE   C   TIME   WCPU COMMAND
  557 root          1 -21  r31   136M 42296K select  0   2:20  9.96% Xorg
 8198 dru           2  52    0   449M 82736K select  3   0:08  5.96% kdeinit4
 8311 dru          27  30    0  1150M   187M uwait   1   1:37  0.98% firefox
  431 root          1  20    0 14268K  1728K select  0   0:06  0.98% moused
 9551 dru           1  21    0 16600K  2660K CPU3    3   0:01  0.98% top
 2357 dru           4  37    0   718M   141M select  0   0:21  0.00% kdeinit4
 8705 dru           4  35    0   480M    98M select  2   0:20  0.00% kdeinit4
 8076 dru           6  20    0   552M   113M uwait   0   0:12  0.00% soffice.bin
 2623 root          1  30   10 12088K  1636K select  3   0:09  0.00% powerd
 2338 dru           1  20    0   440M 84532K select  1   0:06  0.00% kwin
 1427 dru           5  22    0   605M 86412K select  1   0:05  0.00% kdeinit4</screen>

      <para>The output is split into two sections.  The header (the
	first five or six lines) shows the <acronym>PID</acronym> of
	the last process to run, the system load averages (which are a
	measure of how busy the system is), the system uptime (time
	since the last reboot) and the current time.  The other
	figures in the header relate to how many processes are
	running, how much memory and swap space has been used, and how
	much time the system is spending in different CPU states.  If
	the <acronym>ZFS</acronym> file system module has been loaded,
	an <literal>ARC</literal> line indicates how much data was
	read from the memory cache instead of from disk.</para>

      <para>Below the header is a series of columns containing similar
	information to the output from &man.ps.1;, such as the
	<acronym>PID</acronym>, username, amount of CPU time, and the
	command that started the process.  By default, &man.top.1;
	also displays the amount of memory space taken by the process.
	This is split into two columns: one for total size and one for
	resident size.  Total size is how much memory the application
	has needed and the resident size is how much it is actually
	using now.</para>

      <para>&man.top.1; automatically updates the display every two
	seconds.  A different interval can be specified with
	<option>-s</option>.</para>
    </sect2>

    <sect2 xml:id="basics-daemons">
      <title>Killing Processes</title>

      <para>One way to communicate with any running process or daemon
	is to send a <firstterm>signal</firstterm> using &man.kill.1;.
	There are a number of different signals; some have a specific
	meaning while others are described in the application's
	documentation.  A user can only send a signal to a process
	they own and sending a signal to someone else's process will
	result in a permission denied error.  The exception is the
	<systemitem class="username">root</systemitem> user, who can
	send signals to anyone's processes.</para>

      <para>The operating system can also send a signal to a process.
	If an application is badly written and tries to access memory
	that it is not supposed to, &os; will send the process the
	<quote>Segmentation Violation</quote> signal
	(<literal>SIGSEGV</literal>).  If an application has been
	written to use the &man.alarm.3; system call to be alerted
	after a period of time has elapsed, it will be sent the
	<quote>Alarm</quote> signal
	(<literal>SIGALRM</literal>).</para>

      <para>Two signals can be used to stop a process:
	<literal>SIGTERM</literal> and <literal>SIGKILL</literal>.
	<literal>SIGTERM</literal> is the polite way to kill a process
	as the process can read the signal, close any log files it may
	have open, and attempt to finish what it is doing before
	shutting down.  In some cases, a process may ignore
	<literal>SIGTERM</literal> if it is in the middle of some task
	that cannot be interrupted.</para>

      <para><literal>SIGKILL</literal> cannot be ignored by a
	process.  Sending a <literal>SIGKILL</literal> to a
	process will usually stop that process there and then.
	<footnote><para>There are a few tasks that cannot be
	    interrupted.  For example, if the process is trying to
	    read from a file that is on another computer on the
	    network, and the other computer is unavailable, the
	    process is said to be <quote>uninterruptible</quote>.
	    Eventually the process will time out, typically after two
	    minutes.  As soon as this time out occurs the process will
	    be killed.</para></footnote>.</para>

      <para>Other commonly used signals are <literal>SIGHUP</literal>,
	<literal>SIGUSR1</literal>, and <literal>SIGUSR2</literal>.
	Since these are general purpose signals, different
	applications will respond differently.</para>

      <para>For example, after changing a web server's configuration
	file, the web server needs to be told to re-read its
	configuration.  Restarting <command>httpd</command> would
	result in a brief outage period on the web server.  Instead,
	send the daemon the <literal>SIGHUP</literal> signal.  Be
	aware that different daemons will have different behavior, so
	refer to the documentation for the daemon to determine if
	<literal>SIGHUP</literal> will achieve the desired
	results.</para>

      <procedure>
	<title>Sending a Signal to a Process</title>

	<para>This example shows how to send a signal to
	  &man.inetd.8;.  The &man.inetd.8; configuration file is
	  <filename>/etc/inetd.conf</filename>, and &man.inetd.8; will
	  re-read this configuration file when it is sent a
	  <literal>SIGHUP</literal>.</para>

	<step>
	  <para>Find the <acronym>PID</acronym> of the process to send
	    the signal to using &man.pgrep.1;.  In this example, the
	    <acronym>PID</acronym> for &man.inetd.8; is 198:</para>

	  <screen>&prompt.user; <userinput>pgrep -l inetd</userinput>
198  inetd -wW</screen>

	</step>

	<step>
	  <para>Use &man.kill.1; to send the signal.  As
	    &man.inetd.8; is owned by
	    <systemitem class="username">root</systemitem>, use
	    &man.su.1; to become
	    <systemitem class="username">root</systemitem>
	    first.</para>

	  <screen>&prompt.user; <userinput>su</userinput>
<prompt>Password:</prompt>
&prompt.root; <userinput>/bin/kill -s HUP 198</userinput></screen>

	  <para>Like most &unix; commands, &man.kill.1; will not print
	    any output if it is successful.  If a signal is sent to a
	    process not owned by that user, the message
	    <errorname>kill: <replaceable>PID</replaceable>: Operation
	      not permitted</errorname> will be displayed.  Mistyping
	    the <acronym>PID</acronym> will either send the signal to
	    the wrong process, which could have negative results, or
	    will send the signal to a <acronym>PID</acronym> that is
	    not currently in use, resulting in the error
	    <errorname>kill: <replaceable>PID</replaceable>: No such
	      process</errorname>.</para>

	  <note>
	    <title>Why Use <command>/bin/kill</command>?</title>

	    <para>Many shells provide <command>kill</command> as a
	      built in command, meaning that the shell will send the
	      signal directly, rather than running
	      <filename>/bin/kill</filename>.  Be aware that different
	      shells have a different syntax for specifying the name
	      of the signal to send.  Rather than try to learn all of
	      them, it can be simpler to specify
	      <command>/bin/kill</command>.</para>
	  </note>
	</step>
      </procedure>

      <para>When sending other signals, substitute
	<literal>TERM</literal> or <literal>KILL</literal> with the
	name of the signal.</para>

      <important>
	<para>Killing a random process on the system is a bad idea.
	  In particular, &man.init.8;, <acronym>PID</acronym> 1, is
	  special.  Running <command>/bin/kill -s KILL 1</command> is
	  a quick, and unrecommended, way to shutdown the system.
	  <emphasis>Always</emphasis> double check the arguments to
	  &man.kill.1; <emphasis>before</emphasis> pressing
	  <keycap>Return</keycap>.</para>
      </important>
    </sect2>
  </sect1>

  <sect1 xml:id="shells">
    <title>Shells</title>

    <indexterm>
      <primary>shells</primary>
    </indexterm>
    <indexterm>
      <primary>command line</primary>
    </indexterm>

    <para>A <firstterm>shell</firstterm> provides a command line
      interface for interacting with the operating system.  A shell
      receives commands from the input channel and executes them.
      Many shells provide built in functions to help with everyday
      tasks such as file management, file globbing, command line
      editing, command macros, and environment variables.  &os; comes
      with several shells, including the Bourne shell (&man.sh.1;) and
      the extended C shell (&man.tcsh.1;).  Other shells are available
      from the &os; Ports Collection, such as
      <command>zsh</command> and <command>bash</command>.</para>

    <para>The shell that is used is really a matter of taste.  A C
      programmer might feel more comfortable with a C-like shell such
      as &man.tcsh.1;.  A &linux; user might prefer
      <command>bash</command>.  Each shell has unique properties that
      may or may not work with a user's preferred working environment,
      which is why there is a choice of which shell to use.</para>

    <para>One common shell feature is filename completion.  After a
      user types the first few letters of a command or filename and
      presses <keycap>Tab</keycap>, the shell completes the rest of
      the command or filename.  Consider two files called
      <filename>foobar</filename> and <filename>football</filename>.
      To delete <filename>foobar</filename>, the user might type
      <command>rm foo</command> and press <keycap>Tab</keycap> to
      complete the filename.</para>

    <para>But the shell only shows <command>rm foo</command>.  It was
      unable to complete the filename because both
      <filename>foobar</filename> and <filename>football</filename>
      start with <literal>foo</literal>.  Some shells sound a beep or
      show all the choices if more than one name matches.  The user
      must then type more characters to identify the desired filename.
      Typing a <literal>t</literal> and pressing <keycap>Tab</keycap>
      again is enough to let the shell determine which filename is
      desired and fill in the rest.</para>

    <indexterm>
      <primary>environment variables</primary>
    </indexterm>

    <para>Another feature of the shell is the use of environment
      variables.  Environment variables are a variable/key pair stored
      in the shell's environment.  This environment can be read by any
      program invoked by the shell, and thus contains a lot of program
      configuration.  <xref linkend="shell-env-vars"/> provides a list
      of common environment variables and their meanings.  Note that
      the names of environment variables are always in
      uppercase.</para>

    <table xml:id="shell-env-vars" frame="none" pgwide="1">
      <title>Common Environment Variables</title>

      <tgroup cols="2">
	<thead>
	  <row>
	    <entry>Variable</entry>
	    <entry>Description</entry>
	  </row>
	</thead>

	<tbody>
	  <row>
	    <entry><envar>USER</envar></entry>
	    <entry>Current logged in user's name.</entry>
	  </row>

	  <row>
	    <entry><envar>PATH</envar></entry>
	    <entry>Colon-separated list of directories to search for
	      binaries.</entry>
	  </row>

	  <row>
	    <entry><envar>DISPLAY</envar></entry>
	    <entry>Network name of the
	      <application>&xorg;</application>
	      display to connect to, if available.</entry>
	  </row>

	  <row>
	    <entry><envar>SHELL</envar></entry>
	    <entry>The current shell.</entry>
	  </row>

	  <row>
	    <entry><envar>TERM</envar></entry>

	    <entry>The name of the user's type of terminal.  Used to
	      determine the capabilities of the terminal.</entry>
	  </row>

	  <row>
	    <entry><envar>TERMCAP</envar></entry>

	    <entry>Database entry of the terminal escape codes to
	      perform various terminal functions.</entry>
	  </row>

	  <row>
	    <entry><envar>OSTYPE</envar></entry>
	    <entry>Type of operating system.</entry>
	  </row>

	  <row>
	    <entry><envar>MACHTYPE</envar></entry>
	    <entry>The system's CPU architecture.</entry>
	  </row>

	  <row>
	    <entry><envar>EDITOR</envar></entry>
	    <entry>The user's preferred text editor.</entry>
	  </row>

	  <row>
	    <entry><envar>PAGER</envar></entry>
	    <entry>The user's preferred utility for viewing text one
	      page at a time.</entry>
	  </row>

	  <row>
	    <entry><envar>MANPATH</envar></entry>
	    <entry>Colon-separated list of directories to search for
	      manual pages.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <indexterm>
      <primary>Bourne shells</primary>
    </indexterm>

    <para>How to set an environment variable differs between shells.
      In &man.tcsh.1; and &man.csh.1;, use
      <command>setenv</command> to set environment variables.  In
      &man.sh.1; and <command>bash</command>, use
      <command>export</command> to set the current environment
      variables.  This example sets the default <envar>EDITOR</envar>
      to <filename>/usr/local/bin/emacs</filename> for the
      &man.tcsh.1; shell:</para>

    <screen>&prompt.user; <userinput>setenv EDITOR /usr/local/bin/emacs</userinput></screen>

    <para>The equivalent command for <command>bash</command>
      would be:</para>

    <screen>&prompt.user; <userinput>export EDITOR="/usr/local/bin/emacs"</userinput></screen>

    <para>To expand an environment variable in order to see its
      current setting, type a <literal>$</literal> character in front
      of its name on the command line.  For example,
      <command>echo $TERM</command> displays the current
      <envar>$TERM</envar> setting.</para>

    <para>Shells treat special characters, known as meta-characters,
      as special representations of data.  The most common
      meta-character is <literal>*</literal>, which represents any
      number of characters in a filename.  Meta-characters can be used
      to perform filename globbing.  For example, <command>echo
	*</command> is equivalent to <command>ls</command> because
      the shell takes all the files that match <literal>*</literal>
      and <command>echo</command> lists them on the command
      line.</para>

    <para>To prevent the shell from interpreting a special character,
      escape it from the shell by starting it with a backslash
      (<literal>\</literal>).  For example, <command>echo
	$TERM</command> prints the terminal setting whereas
      <command>echo \$TERM</command> literally prints the string
      <literal>$TERM</literal>.</para>

    <sect2 xml:id="changing-shells">
      <title>Changing the Shell</title>

      <para>The easiest way to permanently change the default shell is
	to use <command>chsh</command>.  Running this command will
	open the editor that is configured in the
	<envar>EDITOR</envar> environment variable, which by default
	is set to &man.vi.1;.  Change the <literal>Shell:</literal>
	line to the full path of the new shell.</para>

      <para>Alternately, use <command>chsh -s</command> which will set
	the specified shell without opening an editor.  For example,
	to change the shell to <command>bash</command>:</para>

      <screen>&prompt.user; <userinput>chsh -s /usr/local/bin/bash</userinput></screen>

      <note>
	<para>The new shell <emphasis>must</emphasis> be present in
	  <filename>/etc/shells</filename>.  If the shell was
	  installed from the &os; Ports Collection as described in
	  <xref linkend="ports"/>, it should be automatically added
	  to this file.  If it is missing, add it using this command,
	  replacing the path with the path of the shell:</para>

	<screen>&prompt.root; <userinput>echo <replaceable>/usr/local/bin/bash</replaceable> &gt;&gt; /etc/shells</userinput></screen>

	<para>Then, rerun &man.chsh.1;.</para>
      </note>
    </sect2>

    <sect2>
      <info>
	<title>Advanced Shell Techniques</title>

	<authorgroup>
	  <author>
	    <personname>
	      <firstname>Tom</firstname>
	      <surname>Rhodes</surname>
	    </personname>
	    <contrib>Written by </contrib>
	  </author>
	</authorgroup>
      </info>

      <para>The &unix; shell is not just a command interpreter, it
	acts as a powerful tool which allows users to execute
	commands, redirect their output, redirect their input and
	chain commands together to improve the final command output.
	When this functionality is mixed with built in commands, the
	user is provided with an environment that can maximize
	efficiency.</para>

      <para>Shell redirection is the action of sending the output or
	the input of a command into another command or into a file.
	To capture the output of the &man.ls.1; command, for example,
	into a file, redirect the output:</para>

      <screen>&prompt.user; <userinput>ls &gt; directory_listing.txt</userinput></screen>

      <para>The directory contents will now be listed in
	<filename>directory_listing.txt</filename>.  Some commands can
	be used to read input, such as &man.sort.1;.  To sort this
	listing, redirect the input:</para>

      <screen>&prompt.user; <userinput>sort &lt; directory_listing.txt</userinput></screen>

      <para>The input will be sorted and placed on the screen.  To
	redirect that input into another file, one could redirect the
	output of &man.sort.1; by mixing the direction:</para>

      <screen>&prompt.user; <userinput>sort &lt; directory_listing.txt &gt; sorted.txt</userinput></screen>

      <para>In all of the previous examples, the commands are
	performing redirection using file descriptors.  Every &unix;
	system has file descriptors, which include standard input
	(stdin), standard output (stdout), and standard error
	(stderr).  Each one has a purpose, where input could be a
	keyboard or a mouse, something that provides input.  Output
	could be a screen or paper in a printer.  And error would be
	anything that is used for diagnostic or error messages.  All
	three are considered <acronym>I/O</acronym> based file
	descriptors and sometimes considered streams.</para>

      <para>Through the use of these descriptors, the shell allows
	output and input to be passed around through various commands
	and redirected to or from a file.  Another method of
	redirection is the pipe operator.</para>

      <para>The &unix; pipe operator, <quote>|</quote> allows the
	output of one command to be directly passed or directed to
	another program.  Basically, a pipe allows the standard
	output of a command to be passed as standard input to another
	command, for example:</para>

      <screen>&prompt.user; <userinput>cat directory_listing.txt | sort | less</userinput></screen>

      <para>In that example, the contents of
	<filename>directory_listing.txt</filename> will be sorted and
	the output passed to &man.less.1;.  This allows the user to
	scroll through the output at their own pace and prevent it
	from scrolling off the screen.</para>
    </sect2>
  </sect1>

  <sect1 xml:id="editors">
    <title>Text Editors</title>

    <indexterm>
      <primary>text editors</primary>
    </indexterm>
    <indexterm>
      <primary>editors</primary>
    </indexterm>

    <para>Most &os; configuration is done by editing text files, so
      it is a good idea to become familiar with a
      text editor.  &os; comes with a few as part of the base system,
      and many more are available in the Ports Collection.</para>

    <indexterm>
      <primary><command>ee</command></primary>
    </indexterm>
    <indexterm>
      <primary>editors</primary>
      <secondary>&man.ee.1;</secondary>
    </indexterm>

    <para>A simple editor to learn is &man.ee.1;, which stands for
      easy editor.  To start this editor, type <command>ee
	<replaceable>filename</replaceable></command> where
      <replaceable>filename</replaceable> is the name of the file to
      be edited.  Once inside the editor, all of the commands for
      manipulating the editor's functions are listed at the top of the
      display.  The caret (<literal>^</literal>) represents
      <keycap>Ctrl</keycap>, so <literal>^e</literal> expands to
      <keycombo action="simul">
	<keycap>Ctrl</keycap>
	<keycap>e</keycap>
      </keycombo>.  To leave &man.ee.1;, press <keycap>Esc</keycap>,
      then choose the <quote>leave editor</quote> option from the main
      menu.  The editor will prompt to save any changes if the file
      has been modified.</para>

    <indexterm>
      <primary><command>vi</command></primary>
    </indexterm>
    <indexterm>
      <primary>editors</primary>
    </indexterm>
    <indexterm>
      <primary><command>emacs</command></primary>
    </indexterm>

    <para>&os; also comes with more powerful text editors, such as
      &man.vi.1;, as part of the base system.  Other editors, like
      <package>editors/emacs</package> and
      <package>editors/vim</package>, are part of the
      &os; Ports Collection.  These editors offer more functionality
      at the expense of being more complicated to learn.  Learning a
      more powerful editor such as <application>vim</application> or
      <application>Emacs</application> can save more time in the long
      run.</para>

    <para>Many applications which modify files or require typed input
      will automatically open a text editor.  To change the default
      editor, set the <envar>EDITOR</envar> environment
      variable as described in <xref linkend="shells"/>.</para>
  </sect1>

  <sect1 xml:id="basics-devices">
    <title>Devices and Device Nodes</title>

    <para>A device is a term used mostly for hardware-related
      activities in a system, including disks, printers, graphics
      cards, and keyboards.  When &os; boots, the majority of the boot
      messages refer to devices being detected.  A copy of the boot
      messages are saved to
      <filename>/var/run/dmesg.boot</filename>.</para>

    <para>Each device has a device name and number.  For example,
      <filename>ada0</filename> is the first SATA hard drive,
      while <filename>kbd0</filename> represents the
      keyboard.</para>

    <para>Most devices in &os; must be accessed through special
      files called device nodes, which are located in
      <filename>/dev</filename>.</para>
  </sect1>

  <sect1 xml:id="basics-more-information">
    <title>Manual Pages</title>

    <indexterm>
      <primary>manual pages</primary>
    </indexterm>

    <para>The most comprehensive documentation on &os; is in the form
      of manual pages.  Nearly every program on the system comes with
      a short reference manual explaining the basic operation and
      available arguments.  These manuals can be viewed using
      <command>man</command>:</para>

    <screen>&prompt.user; <userinput>man <replaceable>command</replaceable></userinput></screen>

    <para>where <replaceable>command</replaceable> is the name of the
      command to learn about.  For example, to learn more about
      &man.ls.1;, type:</para>

    <screen>&prompt.user; <userinput>man ls</userinput></screen>

    <para>Manual pages are divided into sections which represent the
      type of topic.  In &os;, the following sections are
      available:</para>

    <orderedlist>
      <listitem>
	<para>User commands.</para>
      </listitem>

      <listitem>
	<para>System calls and error numbers.</para>
      </listitem>

      <listitem>
	<para>Functions in the C libraries.</para>
      </listitem>

      <listitem>
	<para>Device drivers.</para>
      </listitem>

      <listitem>
	<para>File formats.</para>
      </listitem>

      <listitem>
	<para>Games and other diversions.</para>
      </listitem>

      <listitem>
	<para>Miscellaneous information.</para>
      </listitem>

      <listitem>
	<para>System maintenance and operation commands.</para>
      </listitem>

      <listitem>
	<para>System kernel interfaces.</para>
      </listitem>
    </orderedlist>

    <para>In some cases, the same topic may appear in more than one
      section of the online manual.  For example, there is a
      <command>chmod</command> user command and a
      <function>chmod()</function> system call.  To tell &man.man.1;
      which section to display, specify the section number:</para>

    <screen>&prompt.user; <userinput>man 1 chmod</userinput></screen>

    <para>This will display the manual page for the user command
      &man.chmod.1;.  References to a particular section of the
      online manual are traditionally placed in parenthesis in
      written documentation, so &man.chmod.1; refers to the user
      command and &man.chmod.2; refers to the system call.</para>

    <para>If the name of the manual page is unknown, use <command>man
	-k</command> to search for keywords in the manual page
      descriptions:</para>

    <screen>&prompt.user; <userinput>man -k <replaceable>mail</replaceable></userinput></screen>

    <para>This command displays a list of commands that have the
      keyword <quote>mail</quote> in their descriptions.  This is
      equivalent to using &man.apropos.1;.</para>

    <para>To read the descriptions for all of the commands in
      <filename>/usr/bin</filename>, type:</para>

    <screen>&prompt.user; <userinput>cd /usr/bin</userinput>
&prompt.user; <userinput>man -f * | more</userinput></screen>

    <para>or</para>

    <screen>&prompt.user; <userinput>cd /usr/bin</userinput>
&prompt.user; <userinput>whatis * |more</userinput></screen>

    <sect2 xml:id="basics-info">
      <title>GNU Info Files</title>

      <indexterm>
	<primary>Free Software Foundation</primary>
      </indexterm>

      <para>&os; includes several applications and utilities produced
	by the Free Software Foundation (FSF).  In addition to manual
	pages, these programs may include hypertext documents called
	<literal>info</literal> files.  These can be viewed using
	&man.info.1; or, if <package>editors/emacs</package> is
	installed, the info mode of
	<application>emacs</application>.</para>

      <para>To use &man.info.1;, type:</para>

      <screen>&prompt.user; <userinput>info</userinput></screen>

      <para>For a brief introduction, type <literal>h</literal>.  For
	a quick command reference, type <literal>?</literal>.</para>
    </sect2>
  </sect1>
</chapter>