1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
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4 | <!ENTITY % general-entities SYSTEM "../../general.ent">
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5 | %general-entities;
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6 | ]>
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7 |
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8 | <sect1 id="postlfs-config-bootdisk">
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9 | <sect1info>
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10 | <othername>$LastChangedBy$</othername>
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11 | <date>$Date$</date>
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12 | </sect1info>
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13 | <?dbhtml filename="bootdisk.html"?>
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14 | <title>Creating a Custom Boot Disk</title>
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15 |
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16 | <sect2>
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17 | <title>Decent Rescue Boot Disk Needs</title>
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18 | <para>This section is really about creating a <emphasis>rescue</emphasis>
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19 | diskette. As the name <emphasis>rescue</emphasis> implies, the host
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20 | system has a problem, often lost partition information or corrupted file
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21 | systems, that prevents it from booting and/or operating normally. For
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22 | this reason, you <emphasis>must not</emphasis> depend on resources from
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23 | the host being "rescued". To presume that any given partition or hard
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24 | drive <emphasis>will</emphasis> be available is a risky presumption.</para>
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25 |
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26 | <para>Heeding the warning, the rescue disk created here has no
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27 | dependency on the host system's resources, other than basic bootability
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28 | and hardware soundness. At a minimum, the most common sorts of failures
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29 | requiring a rescue boot disk should be addressed by the contents of the
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30 | boot disk. This would include the common loss of partitioning (master
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31 | boot record is lost or corrupted), file system corruption, and the need
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32 | to allow creation and editing of files that may have been lost or
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33 | corrupted, possibly as an effect of the other two problems.</para>
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34 |
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35 | <para>Additional utilities should be available to search for text or
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36 | files, copy, move and remove files, and many other normal operations
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37 | that might be expected to be needed when reconstructing.</para>
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38 | </sect2>
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39 |
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40 | <sect2>
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41 | <title>This Minimal Decent Rescue Disk</title>
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42 |
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43 | <para>The intent here is to create a "rescue boot disk" that will support
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44 | the common operations listed above. These functions are provided by
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45 | including selected executables from <application><ulink
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46 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox
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47 | </ulink></application> and <application><ulink
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48 | url="http://freshmeat.net/projects/e2fsprogs/">e2fsprogs</ulink></application>.
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49 | A basic editor and rudimentary disk partitioning utility may also be
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50 | optionally included.</para>
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51 |
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52 | <para>This, however, is not the limit. A minimal disk is described
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53 | here, but you can add anything you can fit on the floppy. Furthermore,
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54 | if one floppy is not enough to meet your needs, you can make a
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55 | multi-diskette rescue set that means, essentially, the sky is the limit.
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56 | This is discussed below. The number of other possible variations are
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57 | just too numerous to mention here.</para>
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58 | </sect2>
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59 |
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60 | <sect2>
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61 | <title>Build the Rescue Boot Disk</title>
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62 | <sect3>
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63 | <title>Prerequisites</title>
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64 |
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65 | <para>You should have known-good floppy diskettes available. Some
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66 | people prefer to use the <command>fdformat</command> command to prepare
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67 | these because it also does a verification. See the man page for more
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68 | details. Another good idea is to always prepare duplicates of the
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69 | rescue diskette. Media does deteriorate.</para>
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70 |
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71 | <para>These instructions presume a base <acronym>LFS</acronym> install
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72 | using ext2/ext3 file systems.</para>
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73 |
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74 | <para>You need to have loopback device support enabled in your host's
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75 | kernel to use this procedure.</para>
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76 |
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77 | <para>You should make a custom kernel that includes only those features
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78 | needed to rescue your system, so it will have the least size. No
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79 | sense in building in support for things like <application>XFree86</application>,
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80 | <application>DRI</application>, etc, as most rescues are performed from the
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81 | command prompt. Along the same lines, if you have <xref linkend="gcc2"/>, it
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82 | is known to produce smaller kernels. So you might want to use that
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83 | compiler for this kernel. If you do so, don't overlook any loadable
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84 | modules (which are not addressed here) you might need - they need to be
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85 | compiled with the same compiler used to make the kernel.</para>
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86 |
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87 | <para>The rescue image must include support for the file system of your
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88 | choice (we presume ext2/3 here), ramdisk and initial ramdisk (initrd).
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89 | Disable everything that you can in the kernel configuration. You should
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90 | keep support for the proc file system and tempfs file system enabled
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91 | because of their general utility. The proc file system is needed for
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92 | the <command>mount</command> to report properly.</para>
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93 |
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94 | <para>If you install <emphasis>only</emphasis> the minimal set of
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95 | components shown in this document, you will need a kernel that is 643 or
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96 | fewer blocks in size. If you want the optional programs - a very basic
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97 | editor, like <command>ed</command>, and rudimentary disk partitioning, like
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98 | <command>sfdisk</command> - the kernel will need to be 595 or fewer blocks in
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99 | size. This should not be a major problem unless your needs are fairly
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100 | esoteric. On the system used to develop this version of the procedures, using
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101 | only ext2 file systems and not using networking or <acronym>CD</acronym>s for
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102 | recovery, the kernel image is only 481 blocks. And there may be more to gain - it has not been closely examined for additional gains.</para>
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103 |
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104 | <para>This kernel image will be called "rescueimage" hereinafter. You
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105 | can actually name your image anything you like and just use its name
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106 | instead in any commands that include "rescueimage".</para>
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107 |
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108 | <para>If you can not get your rescueimage down to the size needed to allow
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109 | all you need on the ramdisk image, don't fret. You can always build a
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110 | two diskette set, one boot and one root diskette. The kernel will prompt
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111 | you to insert the root file system diskette. This will allow room for a
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112 | compressed ramdisk image of 1440 blocks and a rescueimage of the same
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113 | size.</para>
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114 |
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115 | <para>The rescueimage size limits given above are likely to vary as
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116 | local system-specific configurations change. Use them only as a
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117 | guideline and not as gospel. The size of rescueimage as shown by
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118 | <command>ls -sk</command> is only an approximation because of some
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119 | "overhead". On the system used to develop this version of these
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120 | procedures, that command shows 488 blocks but the actual number of
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121 | blocks written is only 480 and a fraction, which means that 481 blocks
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122 | are actually used.</para>
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123 | </sect3>
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124 |
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125 | <sect3>
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126 | <title>Rescue Disk Build Process</title>
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127 |
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128 | <para>The basic process will be:</para>
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129 | <itemizedlist>
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130 | <listitem><para>make a mount point for a file system</para></listitem>
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131 | <listitem><para>make an empty file to hold the file system</para></listitem>
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132 | <listitem><para>bind the empty file to a loopback device</para></listitem>
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133 | <listitem><para>make a 4MB file system</para></listitem>
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134 | <listitem><para>mount the file system</para></listitem>
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135 | <listitem><para>add components to the file system</para></listitem>
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136 | <listitem><para>make the compressed initrd</para></listitem>
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137 | <listitem><para>join rescueimage and initrd onto a diskette</para></listitem>
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138 | </itemizedlist>
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139 |
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140 | <para>The initial ramdisk will be automatically loaded at boot time if
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141 | setup is done correctly.</para>
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142 |
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143 | <para><emphasis>Make a mount point and an empty file to hold a file
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144 | system</emphasis></para>
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145 |
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146 | <screen><userinput><command>mkdir -p /mnt/loop1
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147 | dd if=/dev/zero of=/tmp/rfloppy bs=1k count=4096</command></userinput></screen>
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148 |
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149 | <para><emphasis>Command explanations</emphasis></para>
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150 |
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151 | <para><command>dd</command>: This is a generalized input-to-output copy
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152 | utility that also has many transformation capabilities.</para>
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153 |
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154 | <para><parameter>if=/dev/zero</parameter>: This parameter assigns
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155 | <command>dd</command>'s input file to a device that returns an infinite
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156 | stream of zeroes.</para>
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157 |
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158 | <para><parameter>of=/tmp/rfloppy</parameter>: This parameter directs
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159 | <command>dd</command>'s output to <filename>/tmp/rfloppy</filename>.</para>
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160 |
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161 | <para><parameter>bs=1k count=4096</parameter>: These parameters tell
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162 | <command>dd</command> to read and write in "chunks" of 1024 bytes and
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163 | process 4096 "chunks".</para>
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164 |
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165 | <para><emphasis>Bind the file to a loopback device, make a file system and mount it.</emphasis></para>
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166 |
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167 | <para>The reason these commands are used is that they work regardless of
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168 | the version of <command>mount</command> (older ones don't have the
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169 | <userinput>-o loop</userinput> option) or if <filename>/etc/mtab</filename>
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170 | is symlinked to <filename class="directory">/proc</filename> (which causes mount to be
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171 | unable to properly "unbind" a loop device, due to "lost" information).
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172 | An alternate set of commands is provided, after these three commands,
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173 | that you can use if you don't have either of these situations.</para>
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174 |
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175 | <screen><userinput><command>losetup /dev/loop1 /tmp/rfloppy
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176 | mke2fs -m 0 -N 504 /dev/loop1
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177 | mount -t ext2 /dev/loop1 /mnt/loop1</command></userinput></screen>
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178 |
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179 | <para><emphasis>Command explanations</emphasis></para>
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180 |
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181 | <para><command>losetup /dev/loop1 /tmp/rfloppy</command>: This
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182 | command "binds" a loopback device to the empty file.</para>
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183 |
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184 | <para><command>mke2fs -m 0 -N 504 /dev/loop1</command>: This
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185 | command makes an ext2 file system on the loopback device (which really
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186 | means it is created in the file to which the loopback device is bound)
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187 | and reserves no blocks. The <userinput>-N 504</userinput> parameter causes
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188 | only 504 inodes to be allocated, leaving more space for other things needed
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189 | in the file system.</para>
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190 |
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191 | <para><command>mount -t ext2 /dev/loop1 /mnt/loop1</command>: This
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192 | mounts the file system just created, just as if it were a real device,
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193 | like a hard drive or diskette. This allows all the normal system I/O
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194 | commands to operate as if a real device were present.</para>
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195 |
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196 | <para>If your <command>mount</command> supports the
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197 | <option>-o loop</option> option <emphasis>and</emphasis> your
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198 | <filename>/etc/mtab</filename> is a real file, rather than a symlink to
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199 | <filename class="directory">/proc</filename>, the three above commands can be replaced
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200 | by these next two commands.</para>
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201 |
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202 | <screen><userinput><command>mke2fs -F -m 0 -N 504 /tmp/rfloppy
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203 | mount -o loop /tmp/rfloppy /mnt/loop1</command></userinput></screen>
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204 |
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205 | <para><emphasis>Command explanations</emphasis></para>
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206 |
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207 | <para><command>mke2fs -F -m 0 -N 504 /tmp/rfloppy</command>: As before,
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208 | a file system is made, with only 504 inodes and no reserved blocks, that
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209 | will be bound to a loopback device. The <userinput>-F</userinput> parameter
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210 | just suppresses an irritating question issued when
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211 | <command>mke2fs</command> realizes that you are not accessing a
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212 | device.</para>
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213 |
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214 | <para><command>mount -o loop /tmp/rfloppy /mnt/loop1</command>: This
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215 | command tells <command>mount</command> to bind the named file to a
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216 | loopback device it automatically selects (the first available) and mount
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217 | the device on <filename class="directory">/mnt/loop1</filename>.</para>
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218 |
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219 | <para><emphasis>Add components to the file system</emphasis></para>
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220 |
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221 | <para><emphasis>A cautionary note:</emphasis> if you are not running in a
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222 | <command>chroot</command> environment, be sure that you do not accidentally
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223 | omit the <filename class="directory">/mnt/loop1</filename> reference in the commands. If
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224 | you do so, you might replace the equivalent components on your host with
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225 | the components that are installed by these procedures. Even if you are
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226 | in a chroot environment, you may need to be careful if the environment
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227 | is your freshly built <acronym>LFS</acronym> system which you intend to
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228 | use as a host in the future.</para>
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229 |
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230 | <para>First, to have as much free space as possible, remove the
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231 | <filename>lost+found</filename> directory, which is not needed because
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232 | it is only used by <command>fsck</command>. Since <command>fsck</command>
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233 | will never be run on this file system, it is unneeded.</para>
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234 |
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235 | <screen><userinput><command>rmdir /mnt/loop1/lost+found/</command></userinput></screen>
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236 |
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237 | <para>Now make a minimal set of directories.</para>
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238 |
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239 | <screen><userinput><command>mkdir /mnt/loop1/{dev,proc,etc,sbin,bin,lib,mnt,usr,var}</command></userinput></screen>
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240 |
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241 | <para>Add needed device files to the initrd image. If you use devfs,
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242 | the following command works well, as you only have the devices you use
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243 | anyway.</para>
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244 |
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245 | <screen><userinput><command>cp -dpR /dev/* /mnt/loop1/dev</command></userinput></screen>
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246 |
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247 | <para>If you used <command>MAKEDEV</command> to create your devices on
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248 | your host, you'll want to use something similar to this longer command,
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249 | to minimize wasting space with unneeded inodes.</para>
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250 |
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251 | <para><emphasis>You must modify this to suit your rescueimage configuration and
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252 | other needs.</emphasis> For example, you may need
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253 | <acronym>SCSI</acronym> devices and may not need
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254 | frame buffer devices or the pseudo-terminal directory. Also, the number
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255 | of hard drives and partitions that you include should be the minimal
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256 | that you need. Extensive analysis has not been done on the list below,
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257 | so there are more inodes and space to be gained by "fine tuning" this
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258 | set.</para>
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259 |
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260 | <screen><userinput><command>mkdir /mnt/loop1/dev/pts
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261 | cp -a \
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262 | /dev/null /dev/console \
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263 | /dev/fb[0-7] /dev/fd /dev/fd0 /dev/fd0h1440 /dev/full \
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264 | /dev/hda* /dev/hdb* /dev/hdc* /dev/hdd* /dev/initctl /dev/kmem \
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265 | /dev/loop[0-3] /dev/lp0 /dev/mem /dev/port \
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266 | /dev/psaux /dev/ram \
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267 | /dev/ram0 /dev/ram1 /dev/ram2 /dev/ram3 /dev/random /dev/rtc \
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268 | /dev/shm /dev/stderr /dev/stdin /dev/stdout /dev/tty \
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269 | /dev/tty[0-9] /dev/ttyS0 /dev/ttyS1 /dev/urandom /dev/zero \
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270 | /mnt/loop1/dev</command></userinput></screen>
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271 |
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272 | <para><emphasis>What is needed in the <filename class="directory">/etc</filename>
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273 | directory</emphasis></para>
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274 |
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275 | <para>If you choose, you can copy all or selected parts of your
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276 | <filename>/etc/passwd</filename> and <filename>/etc/group</filename>
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277 | files. But even if each is less than 1024 bytes, you will lose two
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278 | inodes and two blocks of space on the initial ramdisk. This only really
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279 | matters because of trying to squeeze everything onto a 1.44MB
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280 | diskette. Every little bit helps. The strategy taken here is to create
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281 | these two files as part of the rescue boot and initialization process.
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282 | The commands that make the two files will be embedded inside the
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283 | <filename>rcS</filename> script that <filename>linuxrc</filename>
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284 | (really <application><ulink
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285 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox
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286 | </ulink></application>) invokes after the initrd is
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287 | loaded. This way no more inodes or blocks are used on the
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288 | diskette to carry these files.</para>
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289 |
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290 | <para>Some might like to copy their <filename class="directory">/etc/rc*</filename>
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291 | directory into the ramdisk image, but this may have no value, other
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292 | than archival use, in a worst-case recovery scenario. If you want
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293 | automatic initialization of the system after repair, they may have some
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294 | value. But few people need or want this to happen. If the file system
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295 | on the hard drives are corrupted, what good will mount scripts do? Some
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296 | scripts may be useful, like access to a network to copy over backup data
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297 | when the hard drive's file systems are usable again. The point is that
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298 | you should copy only the parts that you can use because space is at a
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299 | premium on the diskette.</para>
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300 |
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301 | <para>Here, only the <filename>fstab</filename> will be included. This
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302 | is handy because it eases mounting of partitions that may be useful and
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303 | also can be examined and used as a guide as to what is available and
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304 | what may need reconstruction. Because it may be larger than needed, you
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305 | should edit it to remove any useless entries and minimize commentary.
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306 | No other editing is needed because the boot scripts are not included and
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307 | no automatic mounting will be done using the <filename>fstab</filename>.
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308 | If you decide to include some boot scripts that might try to mount
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309 | things, change the <filename>fstab</filename>'s entries to
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310 | <command>noauto</command> in the options field so they don't cause an
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311 | attempt to mount a potentially corrupt partition. Copy it to
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312 | <filename class="directory">/tmp</filename>, edit it as desired and then:</para>
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313 |
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314 | <screen><userinput><command>cp -a /tmp/fstab /mnt/loop1/etc</command></userinput></screen>
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315 |
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316 | <para>Now the initialization script will be added. As mentioned above,
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317 | <command>linuxrc</command> is symlinked to <application><ulink
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318 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox
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319 | </ulink></application>.
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320 | After the kernel and initial ramdisk have been loaded, the kernel gives
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321 | control to <command>linuxrc</command> (<application><ulink
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322 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox
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323 | </ulink></application>). It wants to run an <filename class="directory">/etc/init.d/rcS</filename>
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324 | script to do any initial setup.</para>
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325 |
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326 | <para>If you use devfsd, you will need to set up the
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327 | <filename>rcS</filename> script to handle the devfsd startup. Put the
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328 | following commands in <filename class="directory">/mnt/loop1/etc/init.d/rcS</filename>.
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329 | You may also want to add some of the processes shown in the non-devfs
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330 | version that follows.</para>
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331 |
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332 | <screen><userinput>#!/bin/sh
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333 | mount -t devfs devfs /dev
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334 | /sbin/devfsd /dev</userinput></screen>
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335 |
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336 | <para>If you don't use devfsd, but created a static <filename
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337 | class="directory">/dev</filename>
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338 | directory using <command>MAKEDEV</command>, or any similar process, the
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339 | <filename>rcS</filename> script will do slightly different things.
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340 | Also, don't forget that it is creating the
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341 | <filename>/etc/passwd</filename> and <filename>/etc/group</filename>
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342 | files, thus saving space on the diskette.</para>
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343 |
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344 | <para>The script made next will mount <filename class="directory">/proc</filename>, turn
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345 | on swap (no harm is done if it fails), make the
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346 | <filename>/etc/passwd</filename> and <filename>/etc/group</filename>
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347 | files, create a log directory and turn on swapping. Create the script
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348 | with:</para>
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349 |
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350 | <screen><userinput><command>mkdir -p /mnt/loop1/etc/init.d
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351 | cat >/mnt/loop1/etc/init.d/rcS << EOD</command>
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352 | #!/bin/sh
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353 | mount -t proc proc /proc
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354 | swapon -a
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355 |
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356 | echo "root:x:0:0:root:/root:/bin/bash" > /etc/passwd
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357 |
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358 | <command>cat > /etc/group <<EOF</command>
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359 | root:x:0:
|
---|
360 | bin:x:1:
|
---|
361 | sys:x:2:
|
---|
362 | kmem:x:3:
|
---|
363 | tty:x:4:
|
---|
364 | tape:x:5:
|
---|
365 | daemon:x:6:
|
---|
366 | floppy:x:7:
|
---|
367 | disk:x:8:
|
---|
368 | lp:x:9:
|
---|
369 | dialout:x:10:
|
---|
370 | audio:x:11:
|
---|
371 | <command>EOF
|
---|
372 | chmod 644 /etc/passwd /etc/group</command>
|
---|
373 |
|
---|
374 | mkdir /var/log
|
---|
375 |
|
---|
376 | <command>EOD
|
---|
377 | chmod u+x /mnt/loop1/etc/init.d/rcS</command></userinput></screen>
|
---|
378 |
|
---|
379 | <para>Unless you add a lot to this script, which <emphasis>is</emphasis>
|
---|
380 | encouraged, the above should be reasonably close to what you need.</para>
|
---|
381 |
|
---|
382 | <para><emphasis>Install packages</emphasis></para>
|
---|
383 |
|
---|
384 | <para>There are two packages that must be installed. The <application><ulink
|
---|
385 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox</ulink></application>
|
---|
386 | package incorporates the core functions that provide a shell and many
|
---|
387 | basic utilities. A file system package, like <application><ulink
|
---|
388 | url="http://freshmeat.net/projects/e2fsprogs/">e2fsprogs</ulink></application>, or
|
---|
389 | a package for the file system you are using, will provide a minimal
|
---|
390 | set of utilities for file system checking and reconstruction. The whole
|
---|
391 | package will not be installed, but only certain needed components.</para>
|
---|
392 |
|
---|
393 | <para>If you use devfsd, you will also need to install that software.</para>
|
---|
394 |
|
---|
395 | <para>Install <application><ulink
|
---|
396 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox</ulink></application>
|
---|
397 | into the initial ramdisk image. Busybox incorporates many Unix utility
|
---|
398 | program functions into a single small executable file.</para>
|
---|
399 |
|
---|
400 | <screen><userinput><command>make &&
|
---|
401 | make PREFIX=/mnt/loop1 install &&
|
---|
402 | > /mnt/loop1/var/utmp</command></userinput></screen>
|
---|
403 |
|
---|
404 | <para>A <filename>var/utmp</filename> is made because <application><ulink
|
---|
405 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox</ulink></application>
|
---|
406 | needs it for the reboot command to work properly. If this file doesn't
|
---|
407 | exist when <application><ulink
|
---|
408 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox</ulink></application>
|
---|
409 | is started, the reboot command will not work. This would be a bad thing
|
---|
410 | for people that have no reset button available to them.</para>
|
---|
411 |
|
---|
412 | <para>If you use devfs to create devices on the fly and free up precious
|
---|
413 | inodes on the floppy, you'll also install devfsd to facilitate the
|
---|
414 | devices that <application><ulink
|
---|
415 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox</ulink></application>
|
---|
416 | expects to find. Use the following commands to do the install.</para>
|
---|
417 |
|
---|
418 | <screen><userinput><command>mv GNUmakefile Makefile &&
|
---|
419 | make &&
|
---|
420 | make PREFIX=/mnt/loop1 install</command></userinput></screen>
|
---|
421 |
|
---|
422 | <para><emphasis>Install part of <application>e2fsprogs</application></emphasis></para>
|
---|
423 |
|
---|
424 | <para>If you use the ext2 or ext3 (journaling) file system, you can use
|
---|
425 | the commands below to install the minimal functionality that should
|
---|
426 | allow you to get your hard drives usable again. If you use ext3, keep in
|
---|
427 | mind that it is a part of the <application>e2fsprogs</application>
|
---|
428 | package and you can get the components, which are mostly hard links,
|
---|
429 | from the same places shown below. If you use some other file system,
|
---|
430 | such as reiserfs, you should apply the <emphasis>principals</emphasis>
|
---|
431 | you see here to install parts of that package instead.</para>
|
---|
432 |
|
---|
433 | <screen><userinput><command>LDFLAGS='-s'
|
---|
434 | mkdir build &&
|
---|
435 | cd build &&
|
---|
436 | ../configure --prefix=/mnt/loop1/usr --with-root-prefix="" \
|
---|
437 | --disable-swapfs --disable-debugfs \
|
---|
438 | --enable-dynamic-e2fsck --disable-nls --disable-evms \
|
---|
439 | --disable-rpath &&
|
---|
440 | make LDFLAGS="$LDFLAGS" &&
|
---|
441 | strip -p --strip-unneeded --remove-section=.comment \
|
---|
442 | -o /mnt/loop1/sbin/mke2fs misc/mke2fs &&
|
---|
443 | strip -p --strip-unneeded --remove-section=.comment \
|
---|
444 | -o /mnt/loop1/sbin/e2fsck e2fsck/e2fsck &&
|
---|
445 | chmod 555 /mnt/loop1/sbin/{mke2fs,e2fsck}
|
---|
446 | </command></userinput></screen>
|
---|
447 |
|
---|
448 | <para><emphasis>Two useful utilities</emphasis></para>
|
---|
449 |
|
---|
450 | <para>There are two very useful utilities that any rescue disk should
|
---|
451 | have, to help in faster and more accurate recovery. The first is a
|
---|
452 | partitioning utility. The <command>sfdisk</command> program is
|
---|
453 | used here because of its small size and great power. Be warned though -
|
---|
454 | it is not what is considered to be "user friendly". But the
|
---|
455 | <command>fdisk</command> and <command>cfdisk</command> programs are
|
---|
456 | substantially larger or require more shared objects, like <application>ncurses
|
---|
457 | </application>.</para>
|
---|
458 |
|
---|
459 | <para>The second utility is an editor. Most graphical editors are
|
---|
460 | inherently too large and also require additional shared objects. For
|
---|
461 | this reason, <command>ed</command> is used here. It is small, requires
|
---|
462 | no additional shared objects and is a regex-based editor that is the
|
---|
463 | ancestor to almost all subsequent editors that support regex-based
|
---|
464 | editing, whether graphical or not. It is a "context editor" and offers
|
---|
465 | powerful, but non-graphical, editing features. There are many other
|
---|
466 | editors that may be suitable - feel free to use one of them instead.</para>
|
---|
467 |
|
---|
468 | <para>Read the <application>busybox</application>
|
---|
469 | <filename>INSTALL</filename> and <filename>README</filename> files to
|
---|
470 | see how to include a <command>vi</command> editor. It has not been
|
---|
471 | investigated here yet, so it may or may not easily fit onto a single
|
---|
472 | diskette image such as is made here.</para>
|
---|
473 |
|
---|
474 | <para>You can install these or not, but it is important for you to have
|
---|
475 | some capability such as these offer. Exactly how you would install the
|
---|
476 | utilities you choose will have to be determined by you.</para>
|
---|
477 |
|
---|
478 | <para><command>Sfdisk</command> and <command>ed</command> are installed
|
---|
479 | by, essentially, copying them from your host. Strip is used, just to
|
---|
480 | assure that they carry no "excess baggage", even though the base
|
---|
481 | <acronym>LFS</acronym> install should have stripped them already. Use
|
---|
482 | the following commands:</para>
|
---|
483 |
|
---|
484 | <screen><userinput><command>strip -p --strip-unneeded --remove-section=.comment \
|
---|
485 | -o /mnt/loop1/sbin/sfdisk /sbin/sfdisk
|
---|
486 | strip -p --strip-unneeded --remove-section=.comment \
|
---|
487 | -o /mnt/loop1/bin/ed /bin/ed
|
---|
488 | chmod 555 /mnt/loop1/sbin/sfdisk /mnt/loop1/bin/ed</command></userinput></screen>
|
---|
489 |
|
---|
490 | <para>Also, keeping in mind your space limitations, copy any other
|
---|
491 | binaries and libraries you need to the image. Use the
|
---|
492 | <command>ldd</command> command to see which libraries you will need to
|
---|
493 | copy over for any executables. Don't forget to also strip them
|
---|
494 | <emphasis>before</emphasis> copying them to the ramdisk image or use the
|
---|
495 | <command>strip</command>, as above, to "copy" them.</para>
|
---|
496 |
|
---|
497 | <para><emphasis>Set up the lib directory</emphasis></para>
|
---|
498 |
|
---|
499 | <para>Once you have installed all the utilities from above and any
|
---|
500 | additional ones you want, use the <command>ldd</command> command, as
|
---|
501 | mentioned above, on those that were not listed in this document. If
|
---|
502 | any additional libraries are needed, add them into the setup commands
|
---|
503 | shown next.</para>
|
---|
504 |
|
---|
505 | <para>If you installed only those things shown above, the shared objects
|
---|
506 | needed will be minimal. You can add them to the ramdisk image with:</para>
|
---|
507 |
|
---|
508 | <screen><userinput><command>strip -p --strip-unneeded --remove-section=.comment \
|
---|
509 | -o /mnt/loop1/lib/libc.so.6 /lib/libc-2.3.3.so &&
|
---|
510 | strip -p --strip-unneeded --remove-section=.comment \
|
---|
511 | -o /mnt/loop1/lib/ld-linux.so.2 /lib/ld-2.3.3.so &&
|
---|
512 | strip -p --strip-unneeded --remove-section=.comment \
|
---|
513 | -o /mnt/loop1/lib/libdl.so.2 /lib/libdl-2.3.3.so &&
|
---|
514 | chmod 555 /mnt/loop1/lib/{libc.so.6,ld-linux.so.2,libdl.so.2}</command></userinput></screen>
|
---|
515 |
|
---|
516 | <para>Note that the above commands change the names of the libraries,
|
---|
517 | eliminating the need for the usual symlinks. If you add any additional
|
---|
518 | shared objects, be alert for similar opportunities and also the pitfalls
|
---|
519 | that may be present.</para>
|
---|
520 |
|
---|
521 | <para><emphasis>Make the compressed initrd</emphasis></para>
|
---|
522 |
|
---|
523 | <para>Unmount the loopback file. If you used <command>mount</command>'s
|
---|
524 | <option>-o loop</option> option, the "bond" between the loop device
|
---|
525 | and the file will be removed when the unmount is done. Just omit the
|
---|
526 | <command>losetup -d /dev/loop1</command> from the following
|
---|
527 | sequence. The <userinput>-9</userinput> parameter is used with
|
---|
528 | <command>gzip</command> to make the smallest possible compressed image. To
|
---|
529 | make sure it will fit on the diskette, list the file's size.</para>
|
---|
530 |
|
---|
531 | <screen><userinput><command>umount /mnt/loop1 &&
|
---|
532 | losetup -d /dev/loop1 && # Omit if mount's -o loop was used
|
---|
533 | gzip -9 < /tmp/rfloppy > /tmp/rootfs.gz
|
---|
534 | ls -l /tmp/rootfs.gz</command></userinput></screen>
|
---|
535 |
|
---|
536 | <para><emphasis>Join rescueimage and initrd onto a diskette</emphasis></para>
|
---|
537 |
|
---|
538 | <para>Now the rescueimage and initial ramdisk image will be written to
|
---|
539 | the boot diskette. Before doing this, calculate the number of blocks
|
---|
540 | needed for rescueimage and for <filename>/tmp/rootfs.gz</filename>
|
---|
541 | (the initial ramdisk), individually, by dividing each
|
---|
542 | size by 1024 and adding one if there is any remainder. Add these two
|
---|
543 | results together. They must total 1,440 or fewer blocks. If they total
|
---|
544 | more than this, don't worry too much. Changes to make a two-diskette
|
---|
545 | set are presented later. Of course, you could reexamine your choices and
|
---|
546 | try to shrink either the rescueimage or the initial ramdisk image.</para>
|
---|
547 |
|
---|
548 | <para>To make a single-floppy rescue, using devfs, use the following
|
---|
549 | commands. If you use the static <filename class="directory">/dev</filename> setup, use
|
---|
550 | <filename>/dev/fd0</filename> instead of the /dev/floppy/0.</para>
|
---|
551 |
|
---|
552 | <screen><userinput><command>dd if=rescueimage of=/dev/floppy/0 bs=1k
|
---|
553 | rdev /dev/floppy/0 0,0
|
---|
554 | rdev -R /dev/floppy/0 0</command></userinput></screen>
|
---|
555 |
|
---|
556 | <para><emphasis>Command explanations</emphasis></para>
|
---|
557 |
|
---|
558 | <para><command>rdev /dev/floppy/0 0,0</command>: sets the root file system
|
---|
559 | the kernel will use when it boots. Because it loads an initrd, it will
|
---|
560 | automatically set that as the root device, initially. So, the
|
---|
561 | <option>0,0</option> gives it "no value", telling the kernel to not
|
---|
562 | mount any other device. Some folks give <filename>/dev/fd0</filename> or
|
---|
563 | something similar. But this has effect <emphasis>only</emphasis> when
|
---|
564 | <command>linuxrc</command> (really <application><ulink
|
---|
565 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox
|
---|
566 | </ulink></application>) exits and the normal <command>init</command>
|
---|
567 | processes get invoked. Since this is not being done here, and the floppy
|
---|
568 | is <emphasis>not</emphasis> a valid file system, it would be useless
|
---|
569 | here. A hard drive would be a better choice if you are looking to
|
---|
570 | automatically bring the system up after repair. Since <application><ulink
|
---|
571 | url="http://www.busybox.net/downloads/busybox-0.60.4.tar.bz2">busybox
|
---|
572 | </ulink></application> provides the <command>reboot</command> command,
|
---|
573 | automatic initialization is not needed.</para>
|
---|
574 |
|
---|
575 | <para>The <command>rdev -R /dev/floppy/0 0</command> will set the
|
---|
576 | "root flags" to zero. They have no use in this application.</para>
|
---|
577 |
|
---|
578 | <para>The <command>dd</command> from above showed some results, like</para>
|
---|
579 |
|
---|
580 | <screen> 480+1 records in
|
---|
581 | 480+1 records out</screen>
|
---|
582 |
|
---|
583 | <para>In this example the rescueimage (kernel) was 480+1 blocks in size.
|
---|
584 | Make sure that this number, which may be different for you, matches your
|
---|
585 | calculations from above. You need to calculate a "magic number" now
|
---|
586 | that will be inserted into rescueimage. The value consists of three
|
---|
587 | significant parts. Two are discussed here. The third is touched upon
|
---|
588 | later.</para>
|
---|
589 |
|
---|
590 | <para>Bits 0 - 10 will contain the size of rescueimage, in blocks,
|
---|
591 | that you calculated above, and which should match the results from the
|
---|
592 | dd above. Bit 14 (the 15th bit, which is 2 to the 14th power, or 16,384)
|
---|
593 | is a flag that, when set to 1, tells the kernel an initial ramdisk is to
|
---|
594 | be loaded. So for the single-floppy rescue diskette, the two numbers
|
---|
595 | 16,384 and 481 (or whatever number is right for your rescueimage size) are
|
---|
596 | added together to produce a decimal value, like 16865. This value is
|
---|
597 | inserted into the proper place in rescueimage by the
|
---|
598 | <command>rdev</command> command done next.</para>
|
---|
599 |
|
---|
600 | <para>Insert the "magic number" into rescueimage and then write the
|
---|
601 | root file system right after rescueimage on the floppy by executing the
|
---|
602 | following commands, with the proper numbers inserted. Notice that the
|
---|
603 | <command>seek</command> parameter's number must be the size, in blocks,
|
---|
604 | of your rescueimage. If you use the static <filename class="directory">/dev</filename>
|
---|
605 | setup, use <filename>/dev/fd0</filename> in the commands below, instead
|
---|
606 | of <filename>/dev/floppy/0</filename>.</para>
|
---|
607 |
|
---|
608 | <screen><userinput><command>rdev -r /dev/floppy/0 <replaceable>16865</replaceable>
|
---|
609 | dd if=/tmp/rootfs.gz of=/dev/floppy/0 bs=1k seek=<replaceable>481</replaceable></command></userinput></screen>
|
---|
610 |
|
---|
611 | <para>In this command, <command>seek</command> was used to position to
|
---|
612 | the block following the end of the rescueimage (480+1) and begin writing the
|
---|
613 | root file system to the floppy.</para>
|
---|
614 | </sect3>
|
---|
615 | </sect2>
|
---|
616 |
|
---|
617 | <sect2>
|
---|
618 | <title>A Two-diskette Rescue Setup</title>
|
---|
619 |
|
---|
620 | <para>If you just can't live with a single-diskette rescue system, here
|
---|
621 | is what to do to make a simple two-diskette system. Note that the
|
---|
622 | endless possibilities presented by the availability of
|
---|
623 | <command>linuxrc</command> and other components are not addressed
|
---|
624 | here. Here you will just use the kernel's ability to prompt for a second
|
---|
625 | diskette that contains the initrd image and load it.</para>
|
---|
626 |
|
---|
627 | <para>Modify the above instructions as follows. First a different magic
|
---|
628 | number is needed. The 15th bit (bit 14) still needs to be set, but the
|
---|
629 | size of the rescueimage, in blocks, is replaced with a zero. The third
|
---|
630 | component, which was not discussed above, is now used. This is the 16th
|
---|
631 | bit (bit 15) of the "magic number". When set, it tells the kernel to ask
|
---|
632 | the user to insert the "root" floppy. It then loads the initrd image
|
---|
633 | from that diskette. Because the size of the rescueimage was replaced
|
---|
634 | by zero, the kernel starts loading from the "zero'th" block (the first
|
---|
635 | one) on the second diskette.</para>
|
---|
636 |
|
---|
637 | <para>The 16th bit (bit 15) represents 2 raised to the 15th power, or
|
---|
638 | 32,768. So the new magic number is 32,768 + 16384, which is 49,152. This
|
---|
639 | value tells the kernel to prompt for, and then load, an initial ramdisk
|
---|
640 | image from the first block on the inserted floppy. So your first
|
---|
641 | modification is to the command to write the "magic number" to the rescueimage
|
---|
642 | image on the diskette.</para>
|
---|
643 |
|
---|
644 | <screen><userinput><command>rdev -r /dev/floppy/0 <replaceable>49152</replaceable></command></userinput></screen>
|
---|
645 |
|
---|
646 | <para>Note that the initrd image is <emphasis>not</emphasis> copied to
|
---|
647 | the diskette yet. Remove the boot diskette and insert another diskette
|
---|
648 | that will hold your root file system. Run this modified command (don't
|
---|
649 | forget to use <filename>/dev/fd0</filename> if you don't use devfs).
|
---|
650 | Note that no <command>seek</command> parameter is used.</para>
|
---|
651 |
|
---|
652 | <screen><userinput><command>dd if=/tmp/rootfs.gz of=/dev/floppy/0 bs=1k</command></userinput></screen>
|
---|
653 |
|
---|
654 | <para>That's all there is to it. The possibilities from here are limited only
|
---|
655 | by your imagination and tenacity in pursuing enhancements. And your
|
---|
656 | willingness to research available documentation. A good starting point
|
---|
657 | is the "Documentation" directory in your kernel source tree. More help
|
---|
658 | may be gained at
|
---|
659 | <ulink url="http://linuxfromscratch.org/hints/news.html"><acronym>LFS </acronym> Hints</ulink>
|
---|
660 | (please use a mirror site that is suitable) and
|
---|
661 | <ulink url="http://www.tldp.org">TLDP</ulink>.</para>
|
---|
662 |
|
---|
663 | </sect2>
|
---|
664 | </sect1>
|
---|