1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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3 | "http://www.oasis-open.org/docbook/xml/4.5/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="initramfs">
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9 | <?dbhtml filename="initramfs.html"?>
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10 |
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11 | <sect1info>
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12 | <date>$Date$</date>
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13 | </sect1info>
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14 |
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15 | <title>About initramfs</title>
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16 |
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17 | <para>
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18 | The only purpose of an initramfs is to mount the root filesystem. The
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19 | initramfs is a complete set of directories that you would find on a normal
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20 | root filesystem. It is bundled into a single cpio archive and compressed
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21 | with one of several compression algorithms.
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22 | </para>
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23 |
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24 | <para>
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25 | At boot time, the boot loader loads the kernel and the initramfs image
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26 | into memory and starts the kernel. The kernel checks for the presence
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27 | of the initramfs and, if found, mounts it as / and runs /init. The init
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28 | program is typically a shell script. Note that the boot process takes
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29 | longer, possibly significantly longer, if an initramfs is used.
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30 | </para>
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31 |
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32 | <para>
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33 | For most distributions, kernel modules are the biggest reason to have
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34 | an initramfs. In a general distribution, there are many unknowns such
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35 | as file system types and disk layouts. In a way, this is the opposite
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36 | of LFS where the system capabilities and layout are known and a custom
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37 | kernel is normally built. In this situation, an initramfs is rarely
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38 | needed.
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39 | </para>
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40 |
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41 | <para>
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42 | There are only four primary reasons to have an initramfs in the LFS
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43 | environment: loading the rootfs from a network, loading it from an LVM
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44 | logical volume, having an encrypted rootfs where a password is required, or
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45 | for the convenience of specifying the rootfs as a LABEL or UUID. Anything
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46 | else usually means that the kernel was not configured properly.
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47 | </para>
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48 |
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49 | <sect2 id="initramfs-build">
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50 | <title>Building an initramfs</title>
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51 |
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52 | <para>
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53 | If you do decide to build an initramfs, the following scripts will
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54 | provide a basis to do it. The scripts will allow specifying a rootfs
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55 | via partition UUID or partition LABEL or a rootfs on an LVM logical
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56 | volume. They do not support an encrypted root file system or mounting
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57 | the rootfs over a network card. For a more complete capability see
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58 | <ulink url="https://www.linuxfromscratch.org/hints/read.html"> the LFS
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59 | Hints</ulink> or <ulink
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60 | url="http://fedoraproject.org/wiki/Dracut">dracut</ulink>.
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61 | </para>
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62 |
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63 | <para>
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64 | To install these scripts, run the following commands as the
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65 | <systemitem class="username">root</systemitem> user:
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66 | </para>
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67 |
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68 | <screen role="root"><userinput>cat > /usr/sbin/mkinitramfs << "EOF"
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69 | <literal>#!/bin/bash
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70 | # This file based in part on the mkinitramfs script for the LFS LiveCD
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71 | # written by Alexander E. Patrakov and Jeremy Huntwork.
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72 |
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73 | copy()
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74 | {
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75 | local file
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76 |
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77 | if [ "$2" = "lib" ]; then
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78 | file=$(PATH=/usr/lib type -p $1)
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79 | else
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80 | file=$(type -p $1)
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81 | fi
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82 |
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83 | if [ -n "$file" ] ; then
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84 | cp $file $WDIR/usr/$2
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85 | else
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86 | echo "Missing required file: $1 for directory $2"
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87 | rm -rf $WDIR
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88 | exit 1
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89 | fi
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90 | }
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91 |
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92 | if [ -z $1 ] ; then
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93 | INITRAMFS_FILE=initrd.img-no-kmods
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94 | else
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95 | KERNEL_VERSION=$1
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96 | INITRAMFS_FILE=initrd.img-$KERNEL_VERSION
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97 | fi
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98 |
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99 | if [ -n "$KERNEL_VERSION" ] && [ ! -d "/usr/lib/modules/$1" ] ; then
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100 | echo "No modules directory named $1"
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101 | exit 1
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102 | fi
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103 |
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104 | printf "Creating $INITRAMFS_FILE... "
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105 |
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106 | binfiles="sh cat cp dd killall ls mkdir mknod mount "
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107 | binfiles="$binfiles umount sed sleep ln rm uname"
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108 | binfiles="$binfiles readlink basename"
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109 |
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110 | # Systemd installs udevadm in /bin. Other udev implementations have it in /sbin
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111 | if [ -x /usr/bin/udevadm ] ; then binfiles="$binfiles udevadm"; fi
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112 |
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113 | sbinfiles="modprobe blkid switch_root"
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114 |
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115 | # Optional files and locations
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116 | for f in mdadm mdmon udevd udevadm; do
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117 | if [ -x /usr/sbin/$f ] ; then sbinfiles="$sbinfiles $f"; fi
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118 | done
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119 |
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120 | # Add lvm if present (cannot be done with the others because it
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121 | # also needs dmsetup
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122 | if [ -x /usr/sbin/lvm ] ; then sbinfiles="$sbinfiles lvm dmsetup"; fi
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123 |
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124 | unsorted=$(mktemp /tmp/unsorted.XXXXXXXXXX)
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125 |
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126 | DATADIR=/usr/share/mkinitramfs
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127 | INITIN=init.in
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128 |
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129 | # Create a temporary working directory
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130 | WDIR=$(mktemp -d /tmp/initrd-work.XXXXXXXXXX)
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131 |
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132 | # Create base directory structure
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133 | mkdir -p $WDIR/{dev,run,sys,proc,usr/{bin,lib/{firmware,modules},sbin}}
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134 | mkdir -p $WDIR/etc/{modprobe.d,udev/rules.d}
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135 | touch $WDIR/etc/modprobe.d/modprobe.conf
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136 | ln -s usr/bin $WDIR/bin
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137 | ln -s usr/lib $WDIR/lib
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138 | ln -s usr/sbin $WDIR/sbin
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139 | ln -s lib $WDIR/lib64
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140 |
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141 | # Create necessary device nodes
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142 | mknod -m 640 $WDIR/dev/console c 5 1
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143 | mknod -m 664 $WDIR/dev/null c 1 3
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144 |
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145 | # Install the udev configuration files
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146 | if [ -f /etc/udev/udev.conf ]; then
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147 | cp /etc/udev/udev.conf $WDIR/etc/udev/udev.conf
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148 | fi
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149 |
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150 | for file in $(find /etc/udev/rules.d/ -type f) ; do
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151 | cp $file $WDIR/etc/udev/rules.d
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152 | done
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153 |
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154 | # Install any firmware present
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155 | cp -a /usr/lib/firmware $WDIR/usr/lib
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156 |
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157 | # Copy the RAID configuration file if present
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158 | if [ -f /etc/mdadm.conf ] ; then
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159 | cp /etc/mdadm.conf $WDIR/etc
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160 | fi
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161 |
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162 | # Install the init file
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163 | install -m0755 $DATADIR/$INITIN $WDIR/init
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164 |
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165 | if [ -n "$KERNEL_VERSION" ] ; then
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166 | if [ -x /usr/bin/kmod ] ; then
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167 | binfiles="$binfiles kmod"
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168 | else
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169 | binfiles="$binfiles lsmod"
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170 | sbinfiles="$sbinfiles insmod"
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171 | fi
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172 | fi
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173 |
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174 | # Install basic binaries
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175 | for f in $binfiles ; do
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176 | ldd /usr/bin/$f | sed "s/\t//" | cut -d " " -f1 >> $unsorted
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177 | copy /usr/bin/$f bin
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178 | done
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179 |
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180 | for f in $sbinfiles ; do
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181 | ldd /usr/sbin/$f | sed "s/\t//" | cut -d " " -f1 >> $unsorted
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182 | copy $f sbin
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183 | done
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184 |
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185 | # Add udevd libraries if not in /usr/sbin
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186 | if [ -x /usr/lib/udev/udevd ] ; then
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187 | ldd /usr/lib/udev/udevd | sed "s/\t//" | cut -d " " -f1 >> $unsorted
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188 | elif [ -x /usr/lib/systemd/systemd-udevd ] ; then
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189 | ldd /usr/lib/systemd/systemd-udevd | sed "s/\t//" | cut -d " " -f1 >> $unsorted
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190 | fi
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191 |
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192 | # Add module symlinks if appropriate
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193 | if [ -n "$KERNEL_VERSION" ] && [ -x /usr/bin/kmod ] ; then
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194 | ln -s kmod $WDIR/usr/bin/lsmod
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195 | ln -s kmod $WDIR/usr/bin/insmod
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196 | fi
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197 |
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198 | # Add lvm symlinks if appropriate
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199 | # Also copy the lvm.conf file
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200 | if [ -x /usr/sbin/lvm ] ; then
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201 | ln -s lvm $WDIR/usr/sbin/lvchange
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202 | ln -s lvm $WDIR/usr/sbin/lvrename
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203 | ln -s lvm $WDIR/usr/sbin/lvextend
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204 | ln -s lvm $WDIR/usr/sbin/lvcreate
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205 | ln -s lvm $WDIR/usr/sbin/lvdisplay
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206 | ln -s lvm $WDIR/usr/sbin/lvscan
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207 |
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208 | ln -s lvm $WDIR/usr/sbin/pvchange
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209 | ln -s lvm $WDIR/usr/sbin/pvck
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210 | ln -s lvm $WDIR/usr/sbin/pvcreate
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211 | ln -s lvm $WDIR/usr/sbin/pvdisplay
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212 | ln -s lvm $WDIR/usr/sbin/pvscan
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213 |
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214 | ln -s lvm $WDIR/usr/sbin/vgchange
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215 | ln -s lvm $WDIR/usr/sbin/vgcreate
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216 | ln -s lvm $WDIR/usr/sbin/vgscan
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217 | ln -s lvm $WDIR/usr/sbin/vgrename
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218 | ln -s lvm $WDIR/usr/sbin/vgck
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219 | # Conf file(s)
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220 | cp -a /etc/lvm $WDIR/etc
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221 | fi
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222 |
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223 | # Install libraries
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224 | sort $unsorted | uniq | while read library ; do
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225 | # linux-vdso and linux-gate are pseudo libraries and do not correspond to a file
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226 | # libsystemd-shared is in /lib/systemd, so it is not found by copy, and
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227 | # it is copied below anyway
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228 | if [[ "$library" == linux-vdso.so.1 ]] ||
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229 | [[ "$library" == linux-gate.so.1 ]] ||
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230 | [[ "$library" == libsystemd-shared* ]]; then
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231 | continue
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232 | fi
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233 |
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234 | copy $library lib
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235 | done
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236 |
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237 | if [ -d /usr/lib/udev ]; then
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238 | cp -a /usr/lib/udev $WDIR/usr/lib
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239 | fi
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240 | if [ -d /usr/lib/systemd ]; then
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241 | cp -a /usr/lib/systemd $WDIR/usr/lib
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242 | fi
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243 | if [ -d /usr/lib/elogind ]; then
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244 | cp -a /usr/lib/elogind $WDIR/usr/lib
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245 | fi
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246 |
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247 | # Install the kernel modules if requested
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248 | if [ -n "$KERNEL_VERSION" ]; then
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249 | find \
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250 | /usr/lib/modules/$KERNEL_VERSION/kernel/{crypto,fs,lib} \
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251 | /usr/lib/modules/$KERNEL_VERSION/kernel/drivers/{block,ata,md,firewire} \
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252 | /usr/lib/modules/$KERNEL_VERSION/kernel/drivers/{scsi,message,pcmcia,virtio} \
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253 | /usr/lib/modules/$KERNEL_VERSION/kernel/drivers/usb/{host,storage} \
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254 | -type f 2> /dev/null | cpio --make-directories -p --quiet $WDIR
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255 |
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256 | cp /usr/lib/modules/$KERNEL_VERSION/modules.{builtin,order} \
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257 | $WDIR/usr/lib/modules/$KERNEL_VERSION
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258 |
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259 | depmod -b $WDIR $KERNEL_VERSION
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260 | fi
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261 |
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262 | ( cd $WDIR ; find . | cpio -o -H newc --quiet | gzip -9 ) > $INITRAMFS_FILE
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263 |
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264 | # Prepare early loading of microcode if available
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265 | if ls /usr/lib/firmware/intel-ucode/* >/dev/null 2>&1 ||
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266 | ls /usr/lib/firmware/amd-ucode/* >/dev/null 2>&1; then
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267 |
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268 | # first empty WDIR to reuse it
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269 | rm -r $WDIR/*
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270 |
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271 | DSTDIR=$WDIR/kernel/x86/microcode
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272 | mkdir -p $DSTDIR
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273 |
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274 | if [ -d /usr/lib/firmware/amd-ucode ]; then
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275 | cat /usr/lib/firmware/amd-ucode/microcode_amd*.bin > $DSTDIR/AuthenticAMD.bin
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276 | fi
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277 |
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278 | if [ -d /usr/lib/firmware/intel-ucode ]; then
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279 | cat /usr/lib/firmware/intel-ucode/* > $DSTDIR/GenuineIntel.bin
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280 | fi
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281 |
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282 | ( cd $WDIR; find . | cpio -o -H newc --quiet ) > microcode.img
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283 | cat microcode.img $INITRAMFS_FILE > tmpfile
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284 | mv tmpfile $INITRAMFS_FILE
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285 | rm microcode.img
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286 | fi
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287 |
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288 | # Remove the temporary directories and files
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289 | rm -rf $WDIR $unsorted
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290 | printf "done.\n"
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291 | </literal>
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292 | EOF
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293 |
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294 | chmod 0755 /usr/sbin/mkinitramfs</userinput></screen>
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295 |
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296 | <screen role="root"><userinput>mkdir -p /usr/share/mkinitramfs &&
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297 | cat > /usr/share/mkinitramfs/init.in << "EOF"
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298 | <literal>#!/bin/sh
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299 |
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300 | PATH=/usr/bin:/usr/sbin
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301 | export PATH
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302 |
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303 | problem()
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304 | {
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305 | printf "Encountered a problem!\n\nDropping you to a shell.\n\n"
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306 | sh
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307 | }
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308 |
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309 | no_device()
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310 | {
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311 | printf "The device %s, which is supposed to contain the\n" $1
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312 | printf "root file system, does not exist.\n"
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313 | printf "Please fix this problem and exit this shell.\n\n"
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314 | }
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315 |
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316 | no_mount()
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317 | {
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318 | printf "Could not mount device %s\n" $1
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319 | printf "Sleeping forever. Please reboot and fix the kernel command line.\n\n"
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320 | printf "Maybe the device is formatted with an unsupported file system?\n\n"
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321 | printf "Or maybe filesystem type autodetection went wrong, in which case\n"
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322 | printf "you should add the rootfstype=... parameter to the kernel command line.\n\n"
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323 | printf "Available partitions:\n"
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324 | }
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325 |
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326 | do_mount_root()
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327 | {
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328 | mkdir /.root
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329 | [ -n "$rootflags" ] && rootflags="$rootflags,"
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330 | rootflags="$rootflags$ro"
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331 |
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332 | case "$root" in
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333 | /dev/* ) device=$root ;;
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334 | UUID=* ) eval $root; device="/dev/disk/by-uuid/$UUID" ;;
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335 | PARTUUID=*) eval $root; device="/dev/disk/by-partuuid/$PARTUUID" ;;
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336 | LABEL=* ) eval $root; device="/dev/disk/by-label/$LABEL" ;;
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337 | "" ) echo "No root device specified." ; problem ;;
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338 | esac
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339 |
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340 | while [ ! -b "$device" ] ; do
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341 | no_device $device
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342 | problem
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343 | done
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344 |
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345 | if ! mount -n -t "$rootfstype" -o "$rootflags" "$device" /.root ; then
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346 | no_mount $device
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347 | cat /proc/partitions
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348 | while true ; do sleep 10000 ; done
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349 | else
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350 | echo "Successfully mounted device $root"
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351 | fi
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352 | }
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353 |
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354 | do_try_resume()
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355 | {
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356 | case "$resume" in
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357 | UUID=* ) eval $resume; resume="/dev/disk/by-uuid/$UUID" ;;
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358 | LABEL=*) eval $resume; resume="/dev/disk/by-label/$LABEL" ;;
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359 | esac
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360 |
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361 | if $noresume || ! [ -b "$resume" ]; then return; fi
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362 |
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363 | ls -lH "$resume" | ( read x x x x maj min x
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364 | echo -n ${maj%,}:$min > /sys/power/resume )
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365 | }
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366 |
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367 | init=/sbin/init
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368 | root=
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369 | rootdelay=
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370 | rootfstype=auto
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371 | ro="ro"
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372 | rootflags=
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373 | device=
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374 | resume=
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375 | noresume=false
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376 |
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377 | mount -n -t devtmpfs devtmpfs /dev
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378 | mount -n -t proc proc /proc
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379 | mount -n -t sysfs sysfs /sys
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380 | mount -n -t tmpfs tmpfs /run
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381 |
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382 | read -r cmdline < /proc/cmdline
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383 |
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384 | for param in $cmdline ; do
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385 | case $param in
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386 | init=* ) init=${param#init=} ;;
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387 | root=* ) root=${param#root=} ;;
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388 | rootdelay=* ) rootdelay=${param#rootdelay=} ;;
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389 | rootfstype=*) rootfstype=${param#rootfstype=} ;;
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390 | rootflags=* ) rootflags=${param#rootflags=} ;;
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391 | resume=* ) resume=${param#resume=} ;;
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392 | noresume ) noresume=true ;;
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393 | ro ) ro="ro" ;;
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394 | rw ) ro="rw" ;;
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395 | esac
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396 | done
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397 |
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398 | # udevd location depends on version
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399 | if [ -x /sbin/udevd ]; then
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400 | UDEVD=/sbin/udevd
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401 | elif [ -x /lib/udev/udevd ]; then
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402 | UDEVD=/lib/udev/udevd
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403 | elif [ -x /lib/systemd/systemd-udevd ]; then
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404 | UDEVD=/lib/systemd/systemd-udevd
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405 | else
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406 | echo "Cannot find udevd nor systemd-udevd"
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407 | problem
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408 | fi
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409 |
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410 | ${UDEVD} --daemon --resolve-names=never
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411 | udevadm trigger
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412 | udevadm settle
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413 |
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414 | if [ -f /etc/mdadm.conf ] ; then mdadm -As ; fi
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415 | if [ -x /sbin/vgchange ] ; then /sbin/vgchange -a y > /dev/null ; fi
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416 | if [ -n "$rootdelay" ] ; then sleep "$rootdelay" ; fi
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417 |
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418 | do_try_resume # This function will not return if resuming from disk
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419 | do_mount_root
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420 |
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421 | killall -w ${UDEVD##*/}
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422 |
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423 | exec switch_root /.root "$init" "$@"
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424 | </literal>
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425 | EOF</userinput></screen>
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426 |
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427 | </sect2>
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428 |
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429 | <sect2 id="initramfs-install">
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430 | <title>Using an initramfs</title>
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431 |
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432 | <bridgehead renderas="sect3">Required Runtime Dependency</bridgehead>
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433 |
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434 | <para role="required">
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435 | <xref role="runtime" linkend="cpio"/>
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436 | </para>
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437 |
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438 | <bridgehead renderas="sect3">Other Runtime Dependencies</bridgehead>
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439 |
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440 | <para role="optional">
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441 | <xref role="runtime" linkend="lvm2"/> and/or
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442 | <xref role="runtime" linkend="mdadm"/> must be installed before
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443 | generating the initramfs, if the system partition uses them.
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444 | </para>
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445 |
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446 | <para condition="html" role="usernotes">User Notes:
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447 | <ulink url="&blfs-wiki;/initramfs"/>
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448 | </para>
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449 |
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450 |
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451 | <para>
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452 | To build an initramfs, run the following as the <systemitem
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453 | class="username">root</systemitem> user:
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454 | </para>
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455 |
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456 | <screen role="nodump"><userinput>mkinitramfs [KERNEL VERSION]</userinput></screen>
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457 |
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458 | <para>
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459 | The optional argument is the directory where the appropriate kernel
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460 | modules are located. This must be a subdirectory of <filename
|
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461 | class='directory'> /lib/modules</filename>. If no modules are specified,
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462 | then the initramfs is named <emphasis>initrd.img-no-kmods</emphasis>.
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463 | If a kernel version is specified, the initrd is named
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464 | <emphasis>initrd.img-$KERNEL_VERSION</emphasis> and is only appropriate
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465 | for the specific kernel specified. The output file will be placed in the
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466 | current directory.
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467 | </para>
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468 |
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469 | <para>
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470 | If early loading of microcode is needed (see <xref
|
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471 | linkend="cpu-microcode"/>), you can install the appropriate blob or
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472 | container in <filename class="directory">/lib/firmware</filename>.
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473 | It will be automatically added to the initrd when running
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474 | <command>mkinitramfs</command>.
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475 | </para>
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476 |
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477 | <para>
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478 | After generating the initrd, copy it to the <filename
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479 | class='directory'>/boot</filename> directory.
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480 | </para>
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481 |
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482 | <para>
|
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483 | Now edit <filename>/boot/grub/grub.cfg</filename> and add a new
|
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484 | menuentry. Below are several examples.
|
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485 | </para>
|
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486 |
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487 | <screen role="nodump"><userinput># Generic initramfs and root fs identified by UUID
|
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488 | menuentry "LFS Dev (LFS-7.0-Feb14) initrd, Linux 3.0.4"
|
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489 | {
|
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490 | linux /vmlinuz-3.0.4-lfs-20120214 root=UUID=54b934a9-302d-415e-ac11-4988408eb0a8 ro
|
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491 | initrd /initrd.img-no-kmods
|
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492 | }</userinput></screen>
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493 |
|
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494 | <screen role="nodump"><userinput># Generic initramfs and root fs on LVM partition
|
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495 | menuentry "LFS Dev (LFS-7.0-Feb18) initrd lvm, Linux 3.0.4"
|
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496 | {
|
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497 | linux /vmlinuz-3.0.4-lfs-20120218 root=/dev/mapper/myroot ro
|
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498 | initrd /initrd.img-no-kmods
|
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499 | }</userinput></screen>
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500 |
|
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501 | <screen role="nodump"><userinput># Specific initramfs and root fs identified by LABEL
|
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502 | menuentry "LFS Dev (LFS-7.1-Feb20) initrd label, Linux 3.2.6"
|
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503 | {
|
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504 | linux /vmlinuz-3.2.6-lfs71-120220 root=LABEL=lfs71 ro
|
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505 | initrd /initrd.img-3.2.6-lfs71-120220
|
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506 | }</userinput></screen>
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507 |
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508 | <para>
|
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509 | Finally, reboot the system and select the desired system.
|
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510 | </para>
|
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511 |
|
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512 | </sect2>
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513 |
|
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514 | </sect1>
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