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

     $FreeBSD$
-->

<chapter id="boot">
  <title>The &os; Booting Process</title>

  <sect1 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 simply <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>The basics of &man.device.hints.5;.</para>
      </listitem>
    </itemizedlist>

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

  <sect1 id="boot-introduction">
    <title>The Booting Problem</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, which has
      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.  To do this, 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>

    <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 usually
      referred to as a <emphasis>boot manager</emphasis>, especially
      when it interacts with the user.  In this case, the boot
      manager usually has more code in the first
      <emphasis>track</emphasis> of the disk or within the file
      system of some operating systems.  A boot manager is sometimes
      also called a <emphasis>boot loader</emphasis>, but &os; uses
      that term for a later stage of booting.  Popular boot managers
      include <application>boot0</application>, also called
      <application>Boot Easy</application>, the standard &os; boot
      manager, <application>Grub</application>,
      <application>GAG</application>, and
      <application>LILO</application>.  Only
      <application>boot0</application> fits within the
      <acronym>MBR</acronym>.</para>

    <para>If only one operating system is installed, a standard PC
      <acronym>MBR</acronym> will suffice.  This
      <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.  By default, the
      <acronym>MBR</acronym> installed by &man.fdisk.8; is such an
      <acronym>MBR</acronym> and is based on
      <filename>/boot/mbr</filename>.</para>

    <para>If multiple operating systems are present, a different boot
      manager can be installed which displays the list of operating
      systems so that the user can choose which one to boot from.  Two
      boot managers are discussed in the next subsection.</para>

    <para>The remainder of the &os; bootstrap system is divided
      into three stages.  The first stage is run by the
      <acronym>MBR</acronym>, which 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
      PC standards put 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 it 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 then makes sure the disks are in a
      usable state.  &man.init.8; then 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 on a &os; system at startup.</para>
  </sect1>

  <sect1 id="boot-blocks">
    <title>The Boot Manager and Boot Stages</title>

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

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

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

      <para>The code in the <acronym>MBR</acronym> or boot manager is
	sometimes referred to as <emphasis>stage zero</emphasis> of
	the boot process.  This section discusses two boot managers:
	<application>boot0</application> and
	<application>LILO</application>.</para>

      <formalpara>
	<title>The <application>boot0</application> Boot
	  Manager:</title>

	<para>The <acronym>MBR</acronym> installed by &os;'s installer
	  or &man.boot0cfg.8; 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>
      </formalpara>

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

	<screen>F1 Win
F2 FreeBSD

Default: F2</screen>
      </example>

      <para>Other operating systems, in particular &windows;, 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 <devicename>ad0</devicename> for the first
	<acronym>IDE</acronym> disk, <devicename>ad2</devicename>
	for the first <acronym>IDE</acronym> disk on a second
	<acronym>IDE</acronym> controller, or
	<devicename>da0</devicename>
	for the first <acronym>SCSI</acronym> disk.  To create a
	custom configuration of the <acronym>MBR</acronym>, refer to
	&man.boot0cfg.8;.</para>

      <formalpara>
	<title>The LILO Boot Manager:</title>

	<para>To install this boot manager so it will also boot
	  &os;, boot into Linux and add the following to the existing
	  <filename>/etc/lilo.conf</filename> configuration:</para>
      </formalpara>

      <programlisting>other=/dev/hdXY
table=/dev/hdX
loader=/boot/chain.b
label=FreeBSD</programlisting>

      <para>Specify &os;'s primary partition and drive using Linux
	specifiers, replacing <replaceable>X</replaceable> with the
	Linux drive letter and <replaceable>Y</replaceable> with the
	Linux primary partition number.  For a <acronym>SCSI</acronym>
	drive, change <replaceable>/dev/hd</replaceable> to
	<replaceable>/dev/sd</replaceable>.  The
	<option>loader=/boot/chain.b</option> line can be omitted if
	both operating systems are installed on the same drive.  Next,
	run <command>/sbin/lilo&nbsp;-v</command> to commit the new
	changes.  Verify these are correct by checking the screen
	messages.</para>
    </sect2>

    <sect2 id="boot-boot1">
      <title>Stage One, <filename>/boot/boot1</filename>, and Stage
	Two, <filename>/boot/boot2</filename></title>

      <para>Conceptually, the first and second stages are part of the
	same program, on the same area of the disk.  Because of 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 installer or
	&man.bsdlabel.8;.</para>

      <para>They are located outside file systems, in the first track
	of the boot slice, starting with the first sector.  This is
	where boot0 (<xref linkend="boot-boot0"/>), or any other
	boot manager, expects to find a program to run which will
	continue the boot process.  The number of sectors used is
	easily determined from the size of
	<filename>/boot/boot</filename>.</para>

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

      <para><filename>boot2</filename> is slightly more sophisticated,
	and understands the &os; file system enough to find files, and
	can provide a simple interface to choose the kernel or loader
	to run.</para>

      <para>However, &man.loader.8; is much more sophisticated and
	provides a boot configuration which is run by
	<filename>boot2</filename>.</para>

      <example 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>&man.bsdlabel.8; can be used to replace the installed
	<filename>boot1</filename> and
	<filename>boot2</filename>:</para>

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

      <para>where <replaceable>diskslice</replaceable> is the disk and
	slice to boot from, such as <devicename>ad0s1</devicename>
	for the first slice on the first <acronym>IDE</acronym>
	disk.</para>

      <warning>
	<title>Dangerously Dedicated Mode</title>

	<para>If just the disk name is used, such as
	  <devicename>ad0</devicename>, &man.bsdlabel.8; will create a
	    <quote>dangerously dedicated</quote> disk, without slices.
	  This is probably not the desired action, so double check the
	  <replaceable>diskslice</replaceable> passed to
	  &man.bsdlabel.8; before pressing
	  <keycap>Return</keycap>.</para>
      </warning>
    </sect2>

    <sect2 id="boot-loader">
      <title>Stage Three, <filename>/boot/loader</filename></title>

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

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

      <para>The loader 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>

      <sect3 id="boot-loader-flow">
	<title>Loader Program Flow</title>

	<para>During initialization, the loader 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 loader 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, the loader 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.</para>
      </sect3>

      <sect3 id="boot-loader-commands">
	<title>Loader Built-In Commands</title>

	<para>These are the most commonly used loader commands.  For a
	  complete discussion of all available commands, refer to
	  &man.loader.8;.</para>

	<variablelist>
	  <varlistentry>
	    <term>autoboot <replaceable>seconds</replaceable></term>

	    <listitem>
	      <para>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.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>boot
	      <optional><replaceable>-options</replaceable></optional>
	      <optional><replaceable>kernelname</replaceable></optional></term>

	    <listitem>
	      <para>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
		<emphasis>unload</emphasis> command has been issued;
		otherwise the previously-loaded kernel will be
		used.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>boot-conf</term>

	    <listitem>
	      <para>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.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>help
	      <optional><replaceable>topic</replaceable></optional></term>

	    <listitem>
	      <para>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.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>include <replaceable>filename</replaceable>
	      &hellip;</term>

	    <listitem>
	      <para>Processes the file with the given filename.  The
		file is read in and interpreted line by line.  An
		error immediately stops the include command.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>load <optional><option>-t</option>
	      <replaceable>type</replaceable></optional>
	      <replaceable>filename</replaceable></term>

	    <listitem>
	      <para>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.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>ls <optional><option>-l</option></optional>
	      <optional><replaceable>path</replaceable></optional></term>

	    <listitem>
	      <para>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.</para>
	    </listitem>
	  </varlistentry>

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

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

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

	    <listitem>
	      <para>Displays loaded modules.  If <option>-v</option>
		is specified, more details are shown.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>more <replaceable>filename</replaceable></term>

	    <listitem>
	      <para>Displays the files specified, with a pause at each
		<varname>LINES</varname> displayed.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>reboot</term>

	    <listitem>
	      <para>Immediately reboots the system.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>set <replaceable>variable</replaceable></term>
	    <term>set
	      <replaceable>variable</replaceable>=<replaceable>value</replaceable></term>

	    <listitem>
	      <para>Sets the loader's environment variables.</para>
	    </listitem>
	  </varlistentry>

	  <varlistentry>
	    <term>unload</term>

	    <listitem>
	      <para>Removes all loaded modules.</para>
	    </listitem>
	  </varlistentry>
	</variablelist>
      </sect3>

      <sect3 id="boot-loader-examples">
	<title>Loader Examples</title>

	<para>Here are some practical examples of loader usage:</para>

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

	  <listitem>
	    <para>To boot the usual kernel in single-user mode:</para>

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

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

	    <indexterm>
	      <primary><filename>kernel.old</filename></primary>
	    </indexterm>

	    <screen><userinput>unload</userinput>
<userinput>load <replaceable>kernel.old</replaceable></userinput></screen>

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

	    <note>
	      <para>Use the following to load the usual modules with
		another kernel:</para>

	      <screen><userinput>unload</userinput>
<userinput>set kernel="<replaceable>kernel.old</replaceable>"</userinput>
<userinput>boot-conf</userinput></screen></note>
	  </listitem>

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

	    <screen><userinput>load -t userconfig_script <replaceable>/boot/kernel.conf</replaceable></userinput></screen>
	  </listitem>
	</itemizedlist>
      </sect3>

      <sect3 id="boot-splash">
	<sect3info>
	  <authorgroup>
	    <author>
	      <firstname>Joseph J.</firstname>
	      <surname>Barbish</surname>
	      <contrib>Contributed by </contrib>
	    </author>
	  </authorgroup>
	</sect3info>

	<title>Boot Time Splash Screens</title>

	<para>The splash screen creates an alternate boot screen.  The
	  splash screen hides all the boot probe messages and service
	  startup messages before displaying either a command line or
	  graphical login prompt.</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 the
	  graphical environment as described in <xref linkend="x11"/>.
	  Refer to that chapter for more information on how to install
	  and configure a graphical display manager and a graphical
	  login manager.</para>

	<sect4 id="boot-splash-function">
	  <title>Splash Screen Function</title>

	  <para>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 splash
	    image files must have a resolution of 320 by 200 pixels or
	    less in order to work on standard VGA adapters.</para>

	  <para>To use larger images, up to the maximum resolution of
	    1024 by 768 pixels, load the <acronym>VESA</acronym>
	    module during system boot.  For a custom kernel, as
	    described in <xref linkend="kernelconfig"/>, include the
	    <literal>VESA</literal> kernel configuration option.
	    Loading <acronym>VESA</acronym> support provides the
	    ability to display a splash screen image that fills the
	    whole display screen.</para>

	  <para>While the splash screen is being displayed during the
	    booting process, it can be turned off any time by hitting
	    any key on the keyboard.</para>

	  <para>The splash screen also defaults to being a screen
	    saver outside.  After a time period of non-use, the splash
	    screen will be displayed 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>A few boot loader messages, including the boot options
	    menu and a timed wait count down prompt, are displayed at
	    boot time, even when the splash screen is enabled.</para>

	  <para>Sample splash screen files can be downloaded from the
	    gallery at <ulink
	      url="http://artwork.freebsdgr.org/node/3/">http://artwork.freebsdgr.org</ulink>.
	    By installing the <filename
	      role="package">sysutils/bsd-splash-changer</filename>
	    port, splash images can be chosen from a collection
	    randomly at each boot.</para>
	</sect4>

	<sect4 id="boot-splash-enable">
	  <title>Enabling the Splash Screen Function</title>

	  <para>The splash screen <filename>.bmp</filename>,
	    <filename>.pcx</filename>, or <filename>.bin</filename>
	    image has to be placed on the root partition, for example
	    in <filename class="directory">/boot</filename>.</para>

	  <para>For the default boot display resolution of 256-colors
	    and 320 by 200 pixels or less, edit
	    <filename>/boot/loader.conf</filename> so it contains the
	    following:</para>

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

	  <para>For larger video resolutions up to the maximum of 1024
	    by 768 pixels, edit
	    <filename>/boot/loader.conf</filename>, so it contains the
	    following:</para>

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

	  <para>This example assumes that
	    <filename><replaceable>/boot/splash.bmp</replaceable></filename>
	    is used for the splash screen.  To use a
	    <acronym>PCX</acronym> file, use the following statements,
	    plus the <literal>vesa_load="YES"</literal> line,
	    depending on the resolution:</para>

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

	  <para>Beginning with &os;&nbsp;8.3, another option is to use
	    ASCII art in <ulink
	      url="https://en.wikipedia.org/wiki/TheDraw">TheDraw</ulink>
	    format.</para>

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

	  <para>The file name is not restricted to
	    <quote>splash</quote> as shown in the above example.  It
	    can be anything as long as it is one of the supported
	    types such as,
	    <filename><replaceable>splash_640x400</replaceable>.bmp</filename>
	    or
	    <filename><replaceable>bluewave</replaceable>.pcx</filename>.</para>

	  <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>
	</sect4>
      </sect3>
    </sect2>
  </sect1>

  <sect1 id="boot-kernel">
    <title>Kernel Interaction During Boot</title>

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

    <para>Once the kernel is loaded by either the default loader
      (<xref linkend="boot-loader"/>) or by boot2 (<xref
	linkend="boot-boot1"/>), which bypasses the loader, it
      examines any boot flags and adjusts its behavior as
      necessary.</para>

    <sect2 id="boot-kernel-bootflags">
      <title>Kernel Boot Flags</title>

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

      <para>Here are the more common boot flags:</para>

      <variablelist id="boot-kernel-bootflags-list">
	<varlistentry>
	  <term><option>-a</option></term>

	  <listitem>
	    <para>During kernel initialization, ask for the device
	      to mount as the root file system.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-C</option></term>

	  <listitem>
	    <para>Boot from CDROM.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-c</option></term>

	  <listitem>
	    <para>Run UserConfig, the boot-time kernel
	      configurator.</para>
	  </listitem>
	</varlistentry>

	<varlistentry>
	  <term><option>-s</option></term>

	  <listitem>
	    <para>Boot into single-user mode.</para>
	  </listitem>
	</varlistentry>

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

	  <listitem>
	    <para>Be more verbose during kernel startup.</para>
	  </listitem>
	</varlistentry>
      </variablelist>

      <note>
	<para>Refer to &man.boot.8; for more information on the other
	  boot flags.</para>
      </note>
    </sect2>

<!--    <sect2 id="boot-kernel-userconfig">
      <title>UserConfig: the Boot-time Kernel Configurator</title>

      <para> </para>
    </sect2> -->
  </sect1>

  <sect1 id="device-hints">
    <sect1info>
      <authorgroup>
	<author>
	  <firstname>Tom</firstname>
	  <surname>Rhodes</surname>
	  <contrib>Contributed by </contrib>
	</author>
      </authorgroup>
      <!-- 18 OCT 2002 -->
    </sect1info>

    <title>Device Hints</title>

    <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 id="boot-init">
    <title>Init: Process Control Initialization</title>

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

    <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>.</para>

    <sect2 id="boot-autoreboot">
      <title>Automatic Reboot Sequence</title>

      <para>The automatic reboot sequence makes sure that the file
	systems available on the system are consistent.  If they are
	not, and &man.fsck.8; cannot fix the inconsistencies of a UFS
	file system, &man.init.8; drops the system into single-user
	mode (<xref linkend="boot-singleuser"/>) so that the system
	administrator can resolve the problem directly.</para>
    </sect2>

    <sect2 id="boot-singleuser">
      <title>Single-User Mode</title>

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

      <para>This mode can be reached through the automatic reboot
	sequence (<xref linkend="boot-autoreboot"/>), the user booting
	with <option>-s</option>, or by setting the <envar>boot_
	  single</envar> variable in &man.loader.8;.</para>

      <para>It can also be reached by calling &man.shutdown.8; from
	multi-user mode (<xref linkend="boot-multiuser"/>) without
	including <option>-r</option> or <option>-h</option>.</para>

      <para>If the system <literal>console</literal> is set to
	<literal>insecure</literal> in <filename>/etc/ttys</filename>,
	the system will prompt for the <username>root</username>
	password before initiating single-user mode.</para>

      <example id="boot-insecure-console">
	<title>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 insecure</programlisting>
      </example>

      <note>
	<para>An <literal>insecure</literal> console means that
	  physical security to the console is considered to be
	  insecure, so only someone who knows the
	  <username>root</username> password may use single-user mode.
	  Thus, to add this measure of security, choose
	  <literal>insecure</literal>, instead of the default of
	  <literal>secure</literal>.</para>
      </note>
    </sect2>

    <sect2 id="boot-multiuser">
      <title>Multi-User Mode</title>

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

      <para>If &man.init.8; finds the file systems to be in order, or
	once the user has finished their commands in single-user
	mode (<xref linkend="boot-singleuser"/>), the system enters
	multi-user mode, in which it starts the resource configuration
	of the system.</para>

      <sect3 id="boot-rc">
	<title>Resource Configuration</title>

	<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>, and 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
	  themselves.</para>
      </sect3>
    </sect2>
  </sect1>

  <sect1 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 <username>root</username> or a member of
      <groupname>operator</groupname> 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>

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