RFC: second try at improving Handbook's boot manager text
Gary W. Swearingen
garys at opusnet.com
Wed Sep 14 21:43:51 UTC 2005
A couple of people didn't agree with my grammar and one had some other
comments about the boot manager text of the Handbook (and my change).
So here's another go at it, before I've committed it this time.
There's considerably more to criticize now. :)
I wasn't given much help with the "boot0ext" thing, so I'll leave that
for others to add later.
--- chapter.committed1.sgml Mon Sep 12 08:14:54 2005
+++ chapter.sgml Wed Sep 14 14:24:39 2005
@@ -71,32 +71,44 @@
load the operating system, which has become shortened to
<quote>booting</quote>.</para>
+ <indexterm><primary>BIOS</primary></indexterm>
+
+ <indexterm><primary>Basic Input/Output System</primary><see>BIOS</see></indexterm>
+
<para>On x86 hardware the Basic Input/Output System (BIOS) is responsible
for loading the operating system. To do this, the BIOS looks on the
hard disk for the Master Boot Record (MBR), which must be located on a
specific place on the disk. The BIOS has enough knowledge to load and
run the MBR, and assumes that the MBR can then carry out the rest of the
- tasks involved in loading the operating system.</para>
+ tasks involved in loading the operating system,
+ possibly with the help the BIOS.</para>
+
+ <indexterm><primary>Boot Manager</primary></indexterm>
+
+ <indexterm><primary>Boot Loader</primary></indexterm>
- <indexterm>
- <primary>BIOS</primary>
- </indexterm>
-
- <indexterm>
- <primary>Basic Input/Output System</primary>
- <see>BIOS</see>
- </indexterm>
-
- <para>If you only have one operating system installed on your disks then
- the standard MBR will suffice. This MBR searches for the first bootable
- slice on the disk, and then runs the code on that slice to load the
- remainder of the operating system.</para>
+ <para>The code within the MBR is usually referred to as a <emphasis>boot
+ manager</emphasis>, especially when it interacts with the user; in this case
+ the boot manager usually also has more code in the first
+ <emphasis>track</emphasis> of the disk or within some OS's file system. (A
+ boot manager is sometimes also called a <emphasis>boot loader</emphasis>,
+ but FreeBSD uses that term for a later stage of booting.) Popular boot
+ managers include <application>boot0</application> (a.k.a. <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 MBR.)</para>
+
+ <para>If you have only one operating system installed on your disks then
+ a standard PC MBR will suffice. This MBR searches for the first bootable
+ (a.k.a. active) slice on the disk, and then runs the code on that slice to load the
+ remainder of the operating system. The MBR installed by &man.fdisk.8;,
+ by default, is such an MBR; it is based on <filename>/boot/mbr</filename>.</para>
<para>If you have installed multiple operating systems on your disks then
- you can install a different MBR, one that can display a list of
+ you can install a different boot manager, one that can display a list of
different operating systems, and allows you to choose the one to boot
- from. FreeBSD comes with one such MBR which can be installed, and other
- operating system vendors also provide alternative MBRs.</para>
+ from. Two of these are discussed in the next subsection.</para>
<para>The remainder of the FreeBSD bootstrap system is divided into three
stages. The first stage is run by the MBR, which knows just enough to
@@ -122,29 +134,27 @@
</sect1>
<sect1 id="boot-blocks">
- <title>The MBR, and Boot Stages One, Two, and Three</title>
+ <title>The Boot Manager and Boot Stages</title>
<sect2 id="boot-boot0">
- <title>MBR, <filename>/boot/boot0</filename></title>
+ <title>The Boot Manager</title>
<indexterm><primary>Master Boot Record (MBR)</primary></indexterm>
- <para>The MBR installed by FreeBSD's installer and by boot0cfg(8)
- are based on <filename>/boot/boot0</filename>. The MBR is the first
- sector of a disk, outside slices. (The MBR installed by fdisk(8),
- by default, is based on <filename>/boot/mbr</filename>; it is
- similar to the PC-DOS MBR and it boots the slice marked
- <emphasis>active</emphasis> without prompting the user as the
- FreeBSD MBR does.)
-
- <para><filename>boot0</filename> is very simple, since the
- program in the <abbrev>MBR</abbrev> can only be 512 bytes in
- size.
- (Actually, it can only be 446 bytes because of the slice
- table and the 0x55AA identifier at the end of the MBR).
- If you have installed the FreeBSD MBR and have installed
- multiple operating systems on your hard disks then you will see a
- display similar to this one at boot time:</para>
-
+ <para>The code in the MBR or boot manager is sometimes referred to as
+ <emphasis>stage zero</emphasis> of the boot process. This subsection
+ discusses two of the boot managers previously mentioned:
+ <application>boot0</application> and <application>LILO</application>.</para>
+
+ <formalpara><title>The <application>boot0</application> Boot Manager:</title>
+ <para>The MBR installed by FreeBSD's installer or &man.boot0cfg.8;, by
+ default, is based on <filename>/boot/boot0</filename>.
+ (The <application>boot0</application> program is very simple, since the
+ program in the <abbrev>MBR</abbrev> can only be 446 bytes long because of the slice
+ table and 0x55AA identifier at the end of the MBR.)
+ If you have installed <application>boot0</application> and
+ multiple operating systems on your hard disks, then you will see a
+ display similar to this one at boot time:</para></formalpara>
+
<example id="boot-boot0-example">
<title><filename>boot0</filename> Screenshot</title>
@@ -164,21 +174,23 @@
<screen>&prompt.root; <userinput>fdisk -B -b /boot/boot0 <replaceable>device</replaceable></userinput></screen>
- <para>Where <replaceable>device</replaceable> is the device that you
+ <para>where <replaceable>device</replaceable> is the device that you
boot from, such as <devicename>ad0</devicename> for the first IDE
disk, <devicename>ad2</devicename> for the first IDE disk on a second
IDE controller, <devicename>da0</devicename> for the first SCSI disk,
- and so on.</para>
+ and so on. Or, if you want a custom configuration of the MBR,
+ use &man.boot0cfg.8;.</para>
- <para>If you are a Linux user, however, and prefer that
- <application>LILO</application> control the boot process, you can
- edit the <filename>/etc/lilo.conf</filename> file for FreeBSD, or
- select <option>Leave The Master Boot Record Untouched</option>
- during the FreeBSD installation process. If you have installed the
- FreeBSD boot manager, you can boot back into Linux and modify the
- <application>LILO</application> configuration file
- <filename>/etc/lilo.conf</filename> and add the following
- option:</para>
+ <formalpara><title>The LILO Boot Manager:</title>
+ <para>If you are a Linux user and prefer that
+ <application>LILO</application> control the boot process, you can
+ edit the <filename>/etc/lilo.conf</filename> file for FreeBSD, or
+ select <option>Leave The Master Boot Record Untouched</option>
+ during the FreeBSD installation process. If you have installed the
+ FreeBSD boot manager, you can boot back into Linux and modify the
+ <application>LILO</application> configuration file
+ <filename>/etc/lilo.conf</filename> and add the following
+ option:</para></formalpara>
<programlisting>other=/dev/hdXY
table=/dev/hdb
@@ -192,10 +204,10 @@
will want to change <replaceable>/dev/hdXY</replaceable> to read
something similar to <replaceable>/dev/sdXY</replaceable>, which
again uses the <replaceable>XY</replaceable> syntax. The
- <option>loader=/boot/chain.b</option> can be omitted if you have
+ <option>loader=/boot/chain.b</option> line can be omitted if you have
both operating systems on the same drive. You can now run
<command>/sbin/lilo -v</command> to commit your new changes to the
- system, this should be verified with screen messages.</para>
+ system; this should be verified by its screen messages.</para>
</sect2>
<sect2 id="boot-boot1">
@@ -205,17 +217,18 @@
<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 you would always install them
- together.</para>
-
- <para>They are found on the boot sector of
- the boot slice, which is where <link
- linkend="boot-boot0">boot0</link>, or any other program on the
- <abbrev>MBR</abbrev> expects to find the program to run to
- continue the boot process. The files in the
- <filename>/boot</filename> directory are copies of the real files,
- which are stored outside of the FreeBSD file system.</para>
+ together and they are copied from the combined file
+ <filename>/boot/boot</filename> by the installer or
+ <application>disklabel</application> (see below).</para>
+
+ <para>They are found outside any file system, in the first track of
+ the boot slice, starting with the first sector, which is where <link
+ linkend="boot-boot0">boot0</link>, 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 too
+ <para><filename>boot1</filename> is very simple, since it
can only be 512 bytes
in size, and knows just enough about the FreeBSD
<firstterm>disklabel</firstterm>, which stores information
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