Move init section into Boot Process as the Last Stage.
Format boot options as a table. Expand on single-user mode section. More commits to come. Sponsored by: iXsystems
This commit is contained in:
Dru Lavigne
parent
0abc1317e7
commit
8f8820e88a
Notes:
svn2git
2020-12-08 03:00:23 +00:00
svn path=/head/; revision=44626
1 changed files with 147 additions and 156 deletions
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@ -345,7 +345,7 @@ boot:</screen>
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specified options or kernel name. Providing a kernel
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name on the command-line is only applicable after an
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<command>unload</command> has been issued.
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Otherwise the previously-loaded kernel will be
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Otherwise, the previously-loaded kernel will be
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used.</entry>
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</row>
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@ -432,25 +432,16 @@ boot:</screen>
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</tbody>
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</tgroup>
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</table>
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</sect2>
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<sect2 xml:id="boot-loader-examples">
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<title>Loader Examples</title>
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<para>Here are some practical examples of loader usage:</para>
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<itemizedlist>
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<listitem>
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<para>To boot the usual kernel in single-user
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<para>Here are some practical examples of
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loader usage. To boot the usual kernel in single-user
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mode<indexterm><primary>single-user
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mode</primary></indexterm>:</para>
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<screen><userinput>boot -s</userinput></screen>
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</listitem>
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<listitem>
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<para>To unload the usual kernel and modules, and then
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load the previous or another kernel:</para>
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<para>To unload the usual kernel and modules and then
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load the previous or another, specified kernel:</para>
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<screen><userinput>unload</userinput>
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<userinput>load <replaceable>kernel.old</replaceable></userinput></screen>
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@ -463,94 +454,183 @@ boot:</screen>
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system upgrade or before configuring a custom
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kernel.</para>
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<note>
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<para>Use the following to load the usual modules with
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another kernel:</para>
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<screen><userinput>unload</userinput>
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<userinput>set kernel="<replaceable>kernel.old</replaceable>"</userinput>
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<userinput>boot-conf</userinput></screen></note>
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</listitem>
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<userinput>boot-conf</userinput></screen>
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<listitem>
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<para>To load an automated kernel configuration
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script:</para>
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<screen><userinput>load -t userconfig_script <replaceable>/boot/kernel.conf</replaceable></userinput></screen>
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</listitem>
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</itemizedlist>
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</sect2>
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<sect2 xml:id="boot-kernel">
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<title>Kernel Interaction During Boot</title>
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<indexterm>
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<primary>kernel</primary>
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<secondary>boot interaction</secondary>
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</indexterm>
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</sect2>
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<para>Once the kernel is loaded by either the default loader or
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by boot2, which bypasses the loader, it examines any boot
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flags and adjusts its behavior as necessary.</para>
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<sect2 xml:id="boot-init">
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<title>Last Stage</title>
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<indexterm>
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<primary>&man.init.8;</primary>
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</indexterm>
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<para>Once the kernel is loaded by either <application>loader</application> or
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by <application>boot2</application>, which bypasses
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<application>loader</application>, it examines any boot
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flags and adjusts its behavior as necessary. <xref
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linkend="boot-kernel"/> lists the commonly used boot flags.
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Refer to &man.boot.8; for more information on the other
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boot flags.</para>
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<indexterm>
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<primary>kernel</primary>
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<secondary>bootflags</secondary>
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</indexterm>
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<para>Here are the more common boot flags:</para>
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<table xml:id="boot-kernel" frame="none" pgwide="1">
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<title>Kernel Interaction During Boot</title>
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<variablelist xml:id="boot-kernel-bootflags-list">
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<varlistentry>
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<term><option>-a</option></term>
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<tgroup cols="2">
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<thead>
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<row>
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<entry>Option</entry>
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<entry>Description</entry>
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</row>
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</thead>
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<listitem>
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<para>During kernel initialization, ask for the device
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to mount as the root file system.</para>
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</listitem>
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</varlistentry>
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<tbody>
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<row>
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<entry><option>-a</option></entry>
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<entry>During kernel initialization, ask for the device
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to mount as the root file system.</entry>
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</row>
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<varlistentry>
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<term><option>-C</option></term>
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<row>
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<entry><option>-C</option></entry>
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<entry>Boot the root file system from a <acronym>CDROM</acronym>.</entry>
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</row>
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<listitem>
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<para>Boot from CDROM.</para>
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</listitem>
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</varlistentry>
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<row>
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<entry><option>-s</option></entry>
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<entry>Boot into single-user mode.</entry>
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</row>
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<varlistentry>
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<term><option>-c</option></term>
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<row>
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<entry><option>-v</option></entry>
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<entry>Be more verbose during kernel startup.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<listitem>
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<para>Run UserConfig, the boot-time kernel
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configurator.</para>
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</listitem>
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</varlistentry>
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<para>Once the kernel has finished booting, it passes control to
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the user process &man.init.8;, which is located at
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<filename>/sbin/init</filename>, or the program path specified
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in the <envar>init_path</envar> variable in
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<command>loader</command>. This is the last stage of the boot
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process.</para>
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<varlistentry>
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<term><option>-s</option></term>
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<para>The boot sequence makes sure that the file systems available
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on the system are consistent. If a <acronym>UFS</acronym> file
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system is not, and <command>fsck</command>
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cannot fix the inconsistencies,
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<application>init</application> drops the system into single-user mode so that the
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system administrator can resolve the problem directly. Otherwise,
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the system boots into multi-user mode.</para>
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<listitem>
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<para>Boot into single-user mode.</para>
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</listitem>
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</varlistentry>
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<sect3 xml:id="boot-singleuser">
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<title>Single-User Mode</title>
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<varlistentry>
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<term><option>-v</option></term>
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<indexterm><primary>single-user mode</primary></indexterm>
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<indexterm><primary>console</primary></indexterm>
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<listitem>
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<para>Be more verbose during kernel startup.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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<para>A user can specify this mode by
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booting with <option>-s</option>, or by
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setting the <envar>boot_ single</envar> variable in
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<application>loader</application>. It can also be reached by
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running <command>shutdown now</command> from
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multi-user mode. Single-user mode begins with this message:</para>
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<note>
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<para>Refer to &man.boot.8; for more information on the other
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boot flags.</para>
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</note>
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<programlisting>Enter full pathname of shell or RETURN for /bin/sh:</programlisting>
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<para>If the user presses <keycap>Enter</keycap>, the system
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will enter the default Bourne shell. To specify a different
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shell, input the full path to the shell.</para>
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<para>Single-user mode is usually used to repair a system that will not
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boot due to an inconsistent file system or an error in a boot
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configuration file. It can also be used to reset the
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<systemitem class="username">root</systemitem> password when
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it is unknown. These actions are possible as the single-user
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mode prompt gives full, local access to the system and its
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configuration files. There is no networking in this mode.</para>
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<para>While single-user mode is useful for repairing a system,
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it poses a security risk unless the system is in a physically
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secure location. By default, any user who can gain physical
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access to a system will have full control of that system after
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booting into single-user mode.</para>
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<para>If the system <literal>console</literal> is changed to
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<literal>insecure</literal> in <filename>/etc/ttys</filename>,
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the system will first prompt for the <systemitem
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class="username">root</systemitem> password before
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initiating single-user mode. This adds a measure of security
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while removing the ability to reset the <systemitem
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class="username">root</systemitem> password when it is
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unknown.</para>
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<example xml:id="boot-insecure-console">
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<title>Configuring an Insecure Console in
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<filename>/etc/ttys</filename></title>
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<programlisting># name getty type status comments
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#
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# If console is marked "insecure", then init will ask for the root password
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# when going to single-user mode.
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console none unknown off <replaceable>insecure</replaceable></programlisting>
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</example>
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<para>An <literal>insecure</literal> console means that
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physical security to the console is considered to be
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insecure, so only someone who knows the <systemitem
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class="username">root</systemitem> password may use
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single-user mode.</para>
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</sect3>
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<sect3 xml:id="boot-multiuser">
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<title>Multi-User Mode</title>
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<indexterm><primary>multi-user mode</primary></indexterm>
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<para>If <application>init</application> finds the file systems to be in order, or
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once the user has finished their commands in single-user mode
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and has typed <command>exit</command> to leave single-user mode,
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the system enters
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multi-user mode, in which it starts the resource configuration
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of the system.</para>
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<indexterm><primary>rc files</primary></indexterm>
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<para>The resource configuration system reads in configuration
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defaults from <filename>/etc/defaults/rc.conf</filename> and
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system-specific details from
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<filename>/etc/rc.conf</filename>. It then proceeds to mount
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the system file systems listed in
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<filename>/etc/fstab</filename>. It starts up networking
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services, miscellaneous system daemons, then the startup
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scripts of locally installed packages.</para>
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<para>To learn more about the resource configuration system,
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refer to &man.rc.8; and examine the scripts located in
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<filename>/etc/rc.d</filename>.</para>
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</sect3>
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</sect2>
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</sect1>
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<!--
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<sect2 id="boot-kernel-userconfig">
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<title>UserConfig: the Boot-time Kernel Configurator</title>
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@ -809,95 +889,6 @@ bitmap_name="<replaceable>/boot/splash.bin</replaceable>"</programlisting>
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&man.kenv.1;, &man.loader.conf.5;, and &man.loader.8;.</para>
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</sect1>
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<sect1 xml:id="boot-init">
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<title>Init: Process Control Initialization</title>
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<indexterm>
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<primary>&man.init.8;</primary>
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</indexterm>
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<para>Once the kernel has finished booting, it passes control to
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the user process &man.init.8;, which is located at
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<filename>/sbin/init</filename>, or the program path specified
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in the <envar>init_path</envar> variable in
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<command>loader</command>.</para>
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<para>The boot sequence makes sure that the file systems available
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on the system are consistent. If they are not, and &man.fsck.8;
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cannot fix the inconsistencies of a UFS file system,
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&man.init.8; drops the system into single-user mode so that the
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system administrator can resolve the problem directly.</para>
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<sect2 xml:id="boot-singleuser">
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<title>Single-User Mode</title>
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<indexterm><primary>single-user mode</primary></indexterm>
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<indexterm><primary>console</primary></indexterm>
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<para>This mode can be reached through the automatic reboot
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sequence, the user booting with <option>-s</option>, or by
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setting the <envar>boot_ single</envar> variable in
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&man.loader.8;.</para>
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<para>It can also be reached by calling &man.shutdown.8; from
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multi-user mode (<xref linkend="boot-multiuser"/>) without
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including <option>-r</option> or <option>-h</option>.</para>
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<para>If the system <literal>console</literal> is set to
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<literal>insecure</literal> in <filename>/etc/ttys</filename>,
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the system will prompt for the <systemitem
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class="username">root</systemitem> password before
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initiating single-user mode.</para>
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<example xml:id="boot-insecure-console">
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<title>An Insecure Console in
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<filename>/etc/ttys</filename></title>
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<programlisting># name getty type status comments
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#
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# If console is marked "insecure", then init will ask for the root password
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# when going to single-user mode.
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console none unknown off insecure</programlisting>
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</example>
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<note>
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<para>An <literal>insecure</literal> console means that
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physical security to the console is considered to be
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insecure, so only someone who knows the <systemitem
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class="username">root</systemitem> password may use
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single-user mode. Thus, to add this measure of security,
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choose <literal>insecure</literal>, instead of the default
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of <literal>secure</literal>.</para>
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</note>
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</sect2>
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<sect2 xml:id="boot-multiuser">
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<title>Multi-User Mode</title>
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<indexterm><primary>multi-user mode</primary></indexterm>
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<para>If &man.init.8; finds the file systems to be in order, or
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once the user has finished their commands in single-user mode
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(<xref linkend="boot-singleuser"/>), the system enters
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multi-user mode, in which it starts the resource configuration
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of the system.</para>
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<indexterm><primary>rc files</primary></indexterm>
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<para>The resource configuration system reads in configuration
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defaults from <filename>/etc/defaults/rc.conf</filename>, and
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system-specific details from
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<filename>/etc/rc.conf</filename>, and then proceeds to mount
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the system file systems listed in
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<filename>/etc/fstab</filename>. It starts up networking
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services, miscellaneous system daemons, then the startup
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scripts of locally installed packages.</para>
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<para>To learn more about the resource configuration system,
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refer to &man.rc.8; and examine the scripts themselves.</para>
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</sect2>
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</sect1>
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<sect1 xml:id="boot-shutdown">
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<title>Shutdown Sequence</title>
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