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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="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>>> 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>
…</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>
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