path: root/en_US.ISO8859-1/books/handbook/boot/chapter.xml

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

     $FreeBSD$
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<chapter xmlns="http://docbook.org/ns/docbook"
  xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
  xml:id="boot">

  <title>The &os; Booting Process</title>

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

    <indexterm><primary>booting</primary></indexterm>
    <indexterm><primary>bootstrap</primary></indexterm>

    <para>The process of starting a computer and loading the operating
      system is referred to as <quote>the bootstrap process</quote>,
      or <quote>booting</quote>.  &os;'s boot process provides a great
      deal of flexibility in customizing what happens when the system
      starts, including the ability to select from different operating
      systems installed on the same computer, different versions of
      the same operating system, or a different installed
      kernel.</para>

    <para>This chapter details the configuration options that can be
      set.  It demonstrates how to customize the &os; boot process,
      including everything that happens until the &os; kernel has
      started, probed for devices, and started &man.init.8;.  This
      occurs when the text color of the boot messages changes from
      bright white to grey.</para>

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

    <itemizedlist>
      <listitem>
	<para>The components of the &os; bootstrap system and how they
	  interact.</para>
      </listitem>

      <listitem>
	<para>The options that can be passed to the components in the
	  &os; bootstrap in order to control the boot process.</para>
      </listitem>

      <listitem>
	<para>How to configure a customized boot splash screen.</para>
      </listitem>

      <listitem>
	<para>The basics of setting device hints.</para>
      </listitem>

      <listitem>
	<para>How to boot into single- and multi-user mode and how to
	  properly shut down a &os; system.</para>
      </listitem>
    </itemizedlist>

    <note>
      <para>This chapter only describes the boot process for &os;
	running on x86 and amd64 systems.</para>
    </note>
  </sect1>

  <sect1 xml:id="boot-introduction">
    <title>&os; Boot Process</title>

    <para>Turning on a computer and starting the operating system
      poses an interesting dilemma.  By definition, the computer does
      not know how to do anything until the operating system is
      started.  This includes running programs from the disk.  If the
      computer can not run a program from the disk without the
      operating system, and the operating system programs are on the
      disk, how is the operating system started?</para>

    <para>This problem parallels one in the book <citetitle>The
	Adventures of Baron Munchausen</citetitle>.  A character had
      fallen part way down a manhole, and pulled himself out by
      grabbing his bootstraps and lifting.  In the early days of
      computing, the term <firstterm>bootstrap</firstterm> was applied
      to the mechanism used to load the operating system.  It has
      since become shortened to <quote>booting</quote>.</para>

    <indexterm><primary><acronym>BIOS</acronym></primary></indexterm>

    <indexterm><primary>Basic Input/Output
	System</primary><see><acronym>BIOS</acronym></see></indexterm>

    <para>On x86 hardware, the Basic Input/Output System
      (<acronym>BIOS</acronym>) is responsible for loading the
      operating system.  The <acronym>BIOS</acronym> looks on the hard
      disk for the Master Boot Record (<acronym>MBR</acronym>), which
      must be located in a specific place on the disk.  The
      <acronym>BIOS</acronym> has enough knowledge to load and run the
      <acronym>MBR</acronym>, and assumes that the
      <acronym>MBR</acronym> can then carry out the rest of the tasks
      involved in loading the operating system, possibly with the help
      of the <acronym>BIOS</acronym>.</para>

    <note>
      <para>&os; provides for booting from both the older
	<acronym>MBR</acronym> standard, and the newer GUID Partition
	Table (<acronym>GPT</acronym>).  <acronym>GPT</acronym>
	partitioning is often found on computers with the Unified
	Extensible Firmware Interface (<acronym>UEFI</acronym>).
	However, &os; can boot from <acronym>GPT</acronym> partitions
	even on machines with only a legacy <acronym>BIOS</acronym>
	with &man.gptboot.8;.  Work is under way to provide direct
	<acronym>UEFI</acronym> booting.</para>
    </note>

    <indexterm><primary>Master Boot Record
	(<acronym>MBR</acronym>)</primary></indexterm>

    <indexterm><primary>Boot Manager</primary></indexterm>

    <indexterm><primary>Boot Loader</primary></indexterm>

    <para>The code within the <acronym>MBR</acronym> is typically
      referred to as a <emphasis>boot manager</emphasis>, especially
      when it interacts with the user.  The boot manager usually has
      more code in the first track of the disk or within the file
      system.  Examples of boot managers include the standard &os;
      boot manager <application>boot0</application>, also called
      <application>Boot Easy</application>, and
      <application>Grub</application>, which is used by many &linux;
      distributions.</para>

    <para>If only one operating system is installed, the
      <acronym>MBR</acronym> searches for the first bootable (active)
      slice on the disk, and then runs the code on that slice to load
      the remainder of the operating system.  When multiple operating
      systems are present, a different boot manager can be installed
      to display a list of operating systems so the user
      can select one to boot.</para>

    <para>The remainder of the &os; bootstrap system is divided into
      three stages.  The first stage knows just enough to get the
      computer into a specific state and run the second stage.  The
      second stage can do a little bit more, before running the third
      stage.  The third stage finishes the task of loading the
      operating system.  The work is split into three stages because
      the <acronym>MBR</acronym> puts limits on the size of the
      programs that can be run at stages one and two.  Chaining the
      tasks together allows &os; to provide a more flexible
      loader.</para>

    <indexterm><primary>kernel</primary></indexterm>
    <indexterm><primary>&man.init.8;</primary></indexterm>

    <para>The kernel is then started and begins to probe for devices
      and initialize them for use.  Once the kernel boot process is
      finished, the kernel passes control to the user process
      &man.init.8;, which makes sure the disks are in a usable state,
      starts the user-level resource configuration which mounts file
      systems, sets up network cards to communicate on the network,
      and starts the processes which have been configured to run at
      startup.</para>

    <para>This section describes these stages in more detail and
      demonstrates how to interact with the &os; boot process.</para>

    <sect2 xml:id="boot-boot0">
      <title>The Boot Manager</title>

      <indexterm><primary>Boot Manager</primary></indexterm>

      <indexterm><primary>Master Boot Record
	(<acronym>MBR</acronym>)</primary></indexterm>

      <para>The boot manager code in the <acronym>MBR</acronym> is
	sometimes referred to as <emphasis>stage zero</emphasis> of
	the boot process.  By default, &os; uses the
	<application>boot0</application> boot manager.</para>

      <para>The <acronym>MBR</acronym> installed by the &os; installer
	is based on <filename>/boot/boot0</filename>.  The size and
	capability of <application>boot0</application> is restricted
	to 446 bytes due to the slice table and
	<literal>0x55AA</literal> identifier at the end of the
	<acronym>MBR</acronym>.  If <application>boot0</application>
	and multiple operating systems are installed, a message
	similar to this example will be displayed at boot time:</para>

      <example xml:id="boot-boot0-example">
	<title><filename>boot0</filename> Screenshot</title>

	<screen>F1 Win
F2 FreeBSD

Default: F2</screen>
      </example>

      <para>Other operating systems will overwrite an existing
	<acronym>MBR</acronym> if they are installed after &os;.  If
	this happens, or to replace the existing
	<acronym>MBR</acronym> with the &os; <acronym>MBR</acronym>,
	use the following command:</para>

      <screen>&prompt.root; <userinput>fdisk -B -b /boot/boot0 <replaceable>device</replaceable></userinput></screen>

      <para>where <replaceable>device</replaceable> is the boot disk,
	such as <filename>ad0</filename> for the first
	<acronym>IDE</acronym> disk, <filename>ad2</filename> for the
	first <acronym>IDE</acronym> disk on a second
	<acronym>IDE</acronym> controller, or <filename>da0</filename>
	for the first <acronym>SCSI</acronym> disk.  To create a
	custom configuration of the <acronym>MBR</acronym>, refer to
	&man.boot0cfg.8;.</para>
    </sect2>

    <sect2 xml:id="boot-boot1">
      <title>Stage One and Stage Two</title>

      <para>Conceptually, the first and second stages are part of the
	same program on the same area of the disk.  Due to space
	constraints, they have been split into two, but are always
	installed together.  They are copied from the combined
	<filename>/boot/boot</filename> by the &os; installer or
	<command>bsdlabel</command>.</para>

      <para>These two stages are located outside file systems, in the
	first track of the boot slice, starting with the first sector.
	This is where <application>boot0</application>, or any other
	boot manager, expects to find a program to run which will
	continue the boot process.</para>

      <para>The first stage, <filename>boot1</filename>, is very
	simple, since it can only be 512 bytes in size.  It knows just
	enough about the &os; <firstterm>bsdlabel</firstterm>, which
	stores information about the slice, to find and execute
	<filename>boot2</filename>.</para>

      <para>Stage two, <filename>boot2</filename>, is slightly more
	sophisticated, and understands the &os; file system enough to
	find files.  It can provide a simple interface to choose the
	kernel or loader to run.  It runs
	<application>loader</application>, which is much more
	sophisticated and provides a boot configuration file.  If the
	boot process is interrupted at stage two, the following
	interactive screen is displayed:</para>

      <example xml:id="boot-boot2-example">
	<title><filename>boot2</filename> Screenshot</title>

	<screen>&gt;&gt; FreeBSD/i386 BOOT
Default: 0:ad(0,a)/boot/loader
boot:</screen>
      </example>

      <para>To replace the installed <filename>boot1</filename> and
	<filename>boot2</filename>, use <command>bsdlabel</command>,
	where <replaceable>diskslice</replaceable> is the disk and
	slice to boot from, such as <filename>ad0s1</filename> for the
	first slice on the first <acronym>IDE</acronym> disk:</para>

      <screen>&prompt.root; <userinput>bsdlabel -B <replaceable>diskslice</replaceable></userinput></screen>

      <warning>
	<para>If just the disk name is used, such as
	  <filename>ad0</filename>, <command>bsdlabel</command> will
	  create the disk in <quote>dangerously dedicated
	    mode</quote>, without slices.  This is probably not the
	  desired action, so double check the
	  <replaceable>diskslice</replaceable> before pressing
	  <keycap>Return</keycap>.</para>
      </warning>
    </sect2>

    <sect2 xml:id="boot-loader">
      <title>Stage Three</title>

      <indexterm><primary>boot-loader</primary></indexterm>

      <para>The <application>loader</application> is the final stage
	of the three-stage bootstrap process.  It is located on the
	file system, usually as
	<filename>/boot/loader</filename>.</para>

      <para>The <application>loader</application> is intended as an
	interactive method for configuration, using a built-in command
	set, backed up by a more powerful interpreter which has a more
	complex command set.</para>

      <para>During initialization, <application>loader</application>
	will probe for a console and for disks, and figure out which
	disk it is booting from.  It will set variables accordingly,
	and an interpreter is started where user commands can be
	passed from a script or interactively.</para>

      <indexterm><primary>loader</primary></indexterm>
      <indexterm><primary>loader configuration</primary></indexterm>

      <para>The <application>loader</application> will then read
	<filename>/boot/loader.rc</filename>, which by default reads
	in <filename>/boot/defaults/loader.conf</filename> which sets
	reasonable defaults for variables and reads
	<filename>/boot/loader.conf</filename> for local changes to
	those variables.  <filename>loader.rc</filename> then acts on
	these variables, loading whichever modules and kernel are
	selected.</para>

      <para>Finally, by default, <application>loader</application>
	issues a 10 second wait for key presses, and boots the kernel
	if it is not interrupted.  If interrupted, the user is
	presented with a prompt which understands the command set,
	where the user may adjust variables, unload all modules, load
	modules, and then finally boot or reboot.  <xref
	  linkend="boot-loader-commands"/> lists the most commonly
	used <application>loader</application> commands.  For a
	complete discussion of all available commands, refer to
	&man.loader.8;.</para>

      <table xml:id="boot-loader-commands" frame="none" pgwide="1">
	<title>Loader Built-In Commands</title>

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

	  <tbody>
	    <row>
	      <entry>autoboot
		<replaceable>seconds</replaceable></entry>
	      <entry>Proceeds to boot the kernel if not interrupted
		within the time span given, in seconds.  It displays a
		countdown, and the default time span is 10
		seconds.</entry>
	    </row>

	    <row>
	      <entry>boot
		<optional><replaceable>-options</replaceable></optional>
		<optional><replaceable>kernelname</replaceable></optional></entry>
	      <entry>Immediately proceeds to boot the kernel, with
		any specified options or kernel name.  Providing a
		kernel name on the command-line is only applicable
		after an <command>unload</command> has been issued.
		Otherwise, the previously-loaded kernel will be
		used.  If <emphasis>kernelname</emphasis> is not
		qualified, it will be searched under
		<emphasis>/boot/kernel</emphasis> and
		<emphasis>/boot/modules</emphasis>.</entry>
	    </row>

	    <row>
	      <entry>boot-conf</entry>
	      <entry>Goes through the same automatic configuration of
		modules based on specified variables, most commonly
		<envar>kernel</envar>.  This only makes sense if
		<command>unload</command> is used first, before
		changing some variables.</entry>
	    </row>

	    <row>
	      <entry>help
		<optional><replaceable>topic</replaceable></optional></entry>
	      <entry>Shows help messages read from
		<filename>/boot/loader.help</filename>.  If the topic
		given is <literal>index</literal>, the list of
		available topics is displayed.</entry>
	    </row>

	    <row>
	      <entry>include <replaceable>filename</replaceable>
		&hellip;</entry>
	      <entry>Reads the specified file and interprets it line
		by line.  An error immediately stops the
		<command>include</command>.</entry>
	    </row>

	    <row>
	      <entry>load <optional>-t
		  <replaceable>type</replaceable></optional>
		<replaceable>filename</replaceable></entry>
	      <entry>Loads the kernel, kernel module, or file of the
		type given, with the specified filename.  Any
		arguments after <replaceable>filename</replaceable>
		are passed to the file.  If
		<emphasis>filename</emphasis> is not qualified, it
		will be searched under
		<emphasis>/boot/kernel</emphasis>
		and <emphasis>/boot/modules</emphasis>.</entry>
	    </row>

	    <row>
	      <entry>ls <optional>-l</optional>
		<optional><replaceable>path</replaceable></optional></entry>
	      <entry>Displays a listing of files in the given path, or
		the root directory, if the path is not specified.  If
		<option>-l</option> is specified, file sizes will
		also be shown.</entry>
	    </row>

	    <row>
	      <entry>lsdev <optional>-v</optional></entry>
	      <entry>Lists all of the devices from which it may be
		possible to load modules.  If <option>-v</option> is
		specified, more details are printed.</entry>
	    </row>

	    <row>
	      <entry>lsmod <optional>-v</optional></entry>
	      <entry>Displays loaded modules.  If <option>-v</option>
		is specified, more details are shown.</entry>
	    </row>

	    <row>
	      <entry>more <replaceable>filename</replaceable></entry>
	      <entry>Displays the files specified, with a pause at
		each <varname>LINES</varname> displayed.</entry>
	    </row>

	    <row>
	      <entry>reboot</entry>
	      <entry>Immediately reboots the system.</entry>
	    </row>

	    <row>
	      <entry>set <replaceable>variable</replaceable>, set
		<replaceable>variable</replaceable>=<replaceable>value</replaceable></entry>
	      <entry>Sets the specified environment variables.</entry>
	    </row>

	    <row>
	      <entry>unload</entry>
	      <entry>Removes all loaded modules.</entry>
	    </row>
	  </tbody>
	</tgroup>
      </table>

      <para>Here are some practical examples of loader usage.  To boot
	the usual kernel in single-user mode
	<indexterm><primary>single-user
	  mode</primary></indexterm>:</para>

      <screen><userinput>boot -s</userinput></screen>

      <para>To unload the usual kernel and modules and then load the
	previous or another, specified kernel:</para>

      <screen><userinput>unload</userinput>
<userinput>load <replaceable>/path/to/kernelfile</replaceable></userinput></screen>

      <para>Use the qualified
	<filename>/boot/GENERIC/kernel</filename> to refer to
	the default kernel that comes with an installation, or
	<filename>/boot/kernel.old/kernel</filename>, to refer to the
	previously installed kernel before a system upgrade or before
	configuring a custom kernel.</para>

      <para>Use the following to load the usual modules with another
	kernel.  Note that in this case it is not necessary the
	qualified name:</para>

      <screen><userinput>unload</userinput>
<userinput>set kernel="<replaceable>mykernel</replaceable>"</userinput>
<userinput>boot-conf</userinput></screen>

      <para>To load an automated kernel configuration script:</para>

      <screen><userinput>load -t userconfig_script <replaceable>/boot/kernel.conf</replaceable></userinput></screen>

      <indexterm>
	<primary>kernel</primary>
	<secondary>boot interaction</secondary>
      </indexterm>
    </sect2>

    <sect2 xml:id="boot-init">
      <title>Last Stage</title>

      <indexterm>
	<primary>&man.init.8;</primary>
      </indexterm>

      <para>Once the kernel is loaded by either
	<application>loader</application> or by
	<application>boot2</application>, which bypasses
	<application>loader</application>, it examines any boot flags
	and adjusts its behavior as necessary.  <xref
	  linkend="boot-kernel"/> lists the commonly used boot flags.
	Refer to &man.boot.8; for more information on the other boot
	flags.</para>

      <indexterm>
	<primary>kernel</primary>
	<secondary>bootflags</secondary>
      </indexterm>

      <table xml:id="boot-kernel" frame="none" pgwide="1">
	<title>Kernel Interaction During Boot</title>

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

	  <tbody>
	    <row>
	      <entry><option>-a</option></entry>
	      <entry>During kernel initialization, ask for the device
		to mount as the root file system.</entry>
	    </row>

	    <row>
	      <entry><option>-C</option></entry>
	      <entry>Boot the root file system from a
		<acronym>CDROM</acronym>.</entry>
	    </row>

	    <row>
	      <entry><option>-s</option></entry>
	      <entry>Boot into single-user mode.</entry>
	    </row>

	    <row>
	      <entry><option>-v</option></entry>
	      <entry>Be more verbose during kernel startup.</entry>
	    </row>
	  </tbody>
	</tgroup>
      </table>

      <para>Once the kernel has finished booting, it passes control to
	the user process &man.init.8;, which is located at
	<filename>/sbin/init</filename>, or the program path specified
	in the <envar>init_path</envar> variable in
	<command>loader</command>.  This is the last stage of the boot
	process.</para>

      <para>The boot sequence makes sure that the file systems
	available on the system are consistent.  If a
	<acronym>UFS</acronym> file system is not, and
	<command>fsck</command> cannot fix the inconsistencies,
	<application>init</application> drops the system into
	single-user mode so that the system administrator can resolve
	the problem directly.  Otherwise, the system boots into
	multi-user mode.</para>

      <sect3 xml:id="boot-singleuser">
	<title>Single-User Mode</title>

	<indexterm><primary>single-user mode</primary></indexterm>
	<indexterm><primary>console</primary></indexterm>

	<para>A user can specify this mode by booting with
	  <option>-s</option> or by setting the
	  <envar>boot_single</envar> variable in
	  <application>loader</application>.  It can also be reached
	  by running <command>shutdown now</command> from multi-user
	  mode.  Single-user mode begins with this message:</para>

	<programlisting>Enter full pathname of shell or RETURN for /bin/sh:</programlisting>

	<para>If the user presses <keycap>Enter</keycap>, the system
	  will enter the default Bourne shell.  To specify a different
	  shell, input the full path to the shell.</para>

	<para>Single-user mode is usually used to repair a system that
	  will not boot due to an inconsistent file system or an error
	  in a boot configuration file.  It can also be used to reset
	  the <systemitem class="username">root</systemitem> password
	  when it is unknown.  These actions are possible as the
	  single-user mode prompt gives full, local access to the
	  system and its configuration files.  There is no networking
	  in this mode.</para>

	<para>While single-user mode is useful for repairing a system,
	  it poses a security risk unless the system is in a
	  physically secure location.  By default, any user who can
	  gain physical access to a system will have full control of
	  that system after booting into single-user mode.</para>

	<para>If the system <literal>console</literal> is changed to
	  <literal>insecure</literal> in
	  <filename>/etc/ttys</filename>, the system will first prompt
	  for the <systemitem class="username">root</systemitem>
	  password before initiating single-user mode.  This adds a
	  measure of security while removing the ability to reset the
	  <systemitem class="username">root</systemitem> password when
	  it is unknown.</para>

	<example xml:id="boot-insecure-console">
	  <title>Configuring an Insecure Console in
	    <filename>/etc/ttys</filename></title>

	  <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 <replaceable>insecure</replaceable></programlisting>
	</example>

	<para>An <literal>insecure</literal> console means that
	  physical security to the console is considered to be
	  insecure, so only someone who knows the <systemitem
	    class="username">root</systemitem> password may use
	  single-user mode.</para>
      </sect3>

      <sect3 xml:id="boot-multiuser">
	<title>Multi-User Mode</title>

	<indexterm><primary>multi-user mode</primary></indexterm>

	<para>If <application>init</application> finds the file
	  systems to be in order, or once the user has finished their
	  commands in single-user mode and has typed
	  <command>exit</command> to leave single-user mode, the
	  system enters multi-user mode, in which it starts the
	  resource configuration of the system.</para>

	<indexterm><primary>rc files</primary></indexterm>

	<para>The resource configuration system reads in configuration
	  defaults from <filename>/etc/defaults/rc.conf</filename> and
	  system-specific details from
	  <filename>/etc/rc.conf</filename>.  It then proceeds to
	  mount the system file systems listed in
	  <filename>/etc/fstab</filename>.  It starts up networking
	  services, miscellaneous system daemons, then the startup
	  scripts of locally installed packages.</para>

	<para>To learn more about the resource configuration system,
	  refer to &man.rc.8; and examine the scripts located in
	  <filename>/etc/rc.d</filename>.</para>
      </sect3>
    </sect2>
  </sect1>
  <!--
  <sect2 id="boot-kernel-userconfig">
      <title>UserConfig: the Boot-time Kernel Configurator</title>

      <para> </para>
  </sect2> -->

  <sect1 xml:id="boot-splash">
    <info>
      <title>Configuring Boot Time Splash Screens</title>

      <authorgroup>
	<author>
	  <personname>
	    <firstname>Joseph J.</firstname>
	    <surname>Barbish</surname>
	  </personname>
	  <contrib>Contributed by </contrib>
	</author>
      </authorgroup>
    </info>

    <para>Typically when a &os; system boots, it displays its progress
      as a series of messages at the console.  A boot splash screen
      creates an alternate boot screen that hides all of the boot
      probe and service startup messages.  A few boot loader messages,
      including the boot options menu and a timed wait countdown
      prompt, are displayed at boot time, even when the splash screen
      is enabled.  The display of the splash screen can be turned off
      by hitting any key on the keyboard during the boot
      process.</para>

    <para>There are two basic environments available in &os;.  The
      first is the default legacy virtual console command line
      environment.  After the system finishes booting, a console login
      prompt is presented.  The second environment is a configured
      graphical environment.  Refer to <xref linkend="x11"/> for more
      information on how to install and configure a graphical display
      manager and a graphical login manager.</para>

    <para>Once the system has booted, the splash screen defaults to
      being a screen saver.  After a time period of non-use, the
      splash screen will display and will cycle through steps of
      changing intensity of the image, from bright to very dark and
      over again.  The configuration of the splash screen saver can be
      overridden by adding a <literal>saver=</literal> line to
      <filename>/etc/rc.conf</filename>.  Several built-in screen
      savers are available and described in &man.splash.4;.  The
      <literal>saver=</literal> option only applies to virtual
      consoles and has no effect on graphical display managers.</para>

    <para>By installing the
      <package>sysutils/bsd-splash-changer</package> package or port,
      a random splash image from a collection will display at boot.
      The splash screen function supports 256-colors in the
      bitmap (<filename>.bmp</filename>), ZSoft
      <acronym>PCX</acronym> (<filename>.pcx</filename>), or
      TheDraw (<filename>.bin</filename>) formats.  The
      <filename>.bmp</filename>, <filename>.pcx</filename>, or
      <filename>.bin</filename> image has to be placed on the root
      partition, for example in <filename>/boot</filename>.  The
      splash image files must have a resolution of 320 by 200 pixels
      or less in order to work on standard <acronym>VGA</acronym>
      adapters.  For the default boot display resolution of 256-colors
      and 320 by 200 pixels or less, add the following lines to
      <filename>/boot/loader.conf</filename>.  Replace
      <replaceable>splash.bmp</replaceable> with the name of the
      bitmap file to use:</para>

    <programlisting>splash_bmp_load="YES"
bitmap_load="YES"
bitmap_name="/boot/<replaceable>splash.bmp</replaceable>"</programlisting>

    <para>To use a <acronym>PCX</acronym> file instead of a bitmap
      file:</para>

    <programlisting>splash_pcx_load="YES"
bitmap_load="YES"
bitmap_name="/boot/<replaceable>splash.pcx</replaceable>"</programlisting>

    <para>To instead use ASCII art in the <link
	xlink:href="https://en.wikipedia.org/wiki/TheDraw">https://en.wikipedia.org/wiki/TheDraw</link>
      format:</para>

    <programlisting>splash_txt="YES"
bitmap_load="YES"
bitmap_name="/boot/<replaceable>splash.bin</replaceable>"</programlisting>

    <para>Other interesting <filename>loader.conf</filename> options
      include:</para>

    <variablelist>
      <varlistentry><term><literal>beastie_disable="YES"</literal></term>

	<listitem>
	  <para>This will stop the boot options menu from being
	    displayed, but the timed wait count down prompt will still
	    be present.  Even with the display of the boot options
	    menu disabled, entering an option selection at the timed
	    wait count down prompt will enact the corresponding boot
	    option.</para>
	</listitem>
      </varlistentry>

      <varlistentry><term><literal>loader_logo="beastie"</literal></term>

	<listitem>
	  <para>This will replace the default words
	    <quote>&os;</quote>, which are displayed to the right of
	    the boot options menu, with the colored beastie
	    logo.</para>
	</listitem>
      </varlistentry>
    </variablelist>

    <para>For more information, refer to &man.splash.4;,
      &man.loader.conf.5;, and &man.vga.4;.</para>
  </sect1>

  <sect1 xml:id="device-hints">
    <info>
      <title>Device Hints</title>

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

    <indexterm>
      <primary>device.hints</primary>
    </indexterm>

    <para>During initial system startup, the boot &man.loader.8; reads
      &man.device.hints.5;.  This file stores kernel boot information
      known as variables, sometimes referred to as
      <quote>device hints</quote>.  These <quote>device hints</quote>
      are used by device drivers for device configuration.</para>

    <para>Device hints may also be specified at the Stage 3 boot
      loader prompt, as demonstrated in <xref linkend="boot-loader"/>.
      Variables can be added using <command>set</command>, removed
      with <command>unset</command>, and viewed
      <command>show</command>.  Variables set in
      <filename>/boot/device.hints</filename> can also be overridden.
      Device hints entered at the boot loader are not permanent and
      will not be applied on the next reboot.</para>

    <para>Once the system is booted, &man.kenv.1; can be used to dump
      all of the variables.</para>

    <para>The syntax for <filename>/boot/device.hints</filename>
      is one variable per line, using the hash
      <quote>#</quote> as comment markers.  Lines are constructed as
      follows:</para>

    <screen><userinput>hint.driver.unit.keyword="<replaceable>value</replaceable>"</userinput></screen>

    <para>The syntax for the Stage 3 boot loader is:</para>

    <screen><userinput>set hint.driver.unit.keyword=<replaceable>value</replaceable></userinput></screen>

    <para>where <literal>driver</literal> is the device driver name,
      <literal>unit</literal> is the device driver unit number, and
      <literal>keyword</literal> is the hint keyword.  The keyword may
      consist of the following options:</para>

    <itemizedlist>
      <listitem>
	<para><literal>at</literal>: specifies the bus which the
	  device is attached to.</para>
      </listitem>

      <listitem>
	<para><literal>port</literal>: specifies the start address of
	  the <acronym>I/O</acronym> to be used.</para>
      </listitem>

      <listitem>
	<para><literal>irq</literal>: specifies the interrupt request
	  number to be used.</para>
      </listitem>

      <listitem>
	<para><literal>drq</literal>: specifies the DMA channel
	  number.</para>
      </listitem>

      <listitem>
	<para><literal>maddr</literal>: specifies the physical memory
	  address occupied by the device.</para>
      </listitem>

      <listitem>
	<para><literal>flags</literal>: sets various flag bits for the
	  device.</para>
      </listitem>

      <listitem>
	<para><literal>disabled</literal>: if set to
	  <literal>1</literal> the device is disabled.</para>
      </listitem>
    </itemizedlist>

    <para>Since device drivers may accept or require more hints not
      listed here, viewing a driver's manual page is recommended.
      For more information, refer to &man.device.hints.5;,
      &man.kenv.1;, &man.loader.conf.5;, and &man.loader.8;.</para>
  </sect1>

  <sect1 xml:id="boot-shutdown">
    <title>Shutdown Sequence</title>

    <indexterm>
      <primary>&man.shutdown.8;</primary>
    </indexterm>

    <para>Upon controlled shutdown using &man.shutdown.8;,
      &man.init.8; will attempt to run the script
      <filename>/etc/rc.shutdown</filename>, and then proceed to send
      all processes the <literal>TERM</literal> signal, and
      subsequently the <literal>KILL</literal> signal to any that do
      not terminate in a timely manner.</para>

    <para>To power down a &os; machine on architectures and systems
      that support power management, use

      <command>shutdown -p now</command> to turn the power off
      immediately.  To reboot a &os; system, use
      <command>shutdown -r now</command>.  One must be
      <systemitem class="username">root</systemitem> or a member of
      <systemitem class="groupname">operator</systemitem> in order to
      run &man.shutdown.8;.  One can also use &man.halt.8; and
      &man.reboot.8;.  Refer to their manual pages and to
      &man.shutdown.8; for more information.</para>

    <para>Modify group membership by referring to
      <xref linkend="users-synopsis"/>.</para>

    <note>
      <para>Power management requires &man.acpi.4; to be loaded as
	a module or statically compiled into a custom kernel.</para>
    </note>
  </sect1>
</chapter>