1 | <?xml version="1.0" encoding="UTF-8"?>
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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="ch-system-pkgmgt">
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9 | <?dbhtml filename="pkgmgt.html"?>
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10 |
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11 | <title>Package Management</title>
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12 |
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13 | <para>Package Management is an often requested addition to the LFS Book. A
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14 | Package Manager tracks the installation of files, making it easier to
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15 | remove and upgrade packages. A good package manager will also handle the
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16 | configuration files specially to keep the user configuration when the
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17 | package is reinstalled or upgraded. Before
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18 | you begin to wonder, NO—this section will not talk about nor recommend
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19 | any particular package manager. What it does provide is a roundup of the more
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20 | popular techniques and how they work. The perfect package manager for you may
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21 | be among these techniques, or it may be a combination of two or more of these
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22 | techniques. This section briefly mentions issues that may arise when upgrading
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23 | packages.</para>
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24 |
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25 | <para>Some reasons why no package manager is mentioned in LFS or BLFS
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26 | include:</para>
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27 |
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28 | <itemizedlist>
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29 | <listitem>
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30 | <para>Dealing with package management takes the focus away from the goals
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31 | of these books—teaching how a Linux system is built.</para>
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32 | </listitem>
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33 |
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34 | <listitem>
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35 | <para>There are multiple solutions for package management, each having
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36 | its strengths and drawbacks. Finding one solution that satisfies all audiences
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37 | is difficult.</para>
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38 | </listitem>
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39 | </itemizedlist>
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40 |
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41 | <para>There are some hints written on the topic of package management. Visit
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42 | the <ulink url="&hints-root;">Hints Project</ulink> and see if one of them
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43 | fits your needs.</para>
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44 |
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45 | <sect2 id='pkgmgmt-upgrade-issues'>
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46 | <title>Upgrade Issues</title>
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47 |
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48 | <para>A Package Manager makes it easy to upgrade to newer versions when they
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49 | are released. Generally the instructions in the LFS and BLFS books can be
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50 | used to upgrade to the newer versions. Here are some points that you should
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51 | be aware of when upgrading packages, especially on a running system.</para>
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52 |
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53 | <itemizedlist>
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54 | <listitem>
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55 | <para>If the Linux kernel needs to be upgraded (for example, from
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56 | 5.10.17 to 5.10.18 or 5.11.1), nothing else needs to be rebuilt.
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57 | The system will keep working fine thanks to the well-defined interface
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58 | between the kernel and userspace. Specifically, Linux API headers
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59 | need not be upgraded
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60 | along with the kernel. You will merely need to reboot your system to use the
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61 | upgraded kernel.</para>
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62 | </listitem>
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63 |
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64 | <listitem>
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65 | <para>If Glibc needs to be upgraded to a newer
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66 | version, (e.g., from Glibc-2.36 to Glibc-&glibc-version;),
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67 | some extra steps are needed to avoid breaking the system.
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68 | Read <xref linkend='ch-system-glibc'/> for details.</para>
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69 | </listitem>
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70 |
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71 | <listitem> <para>If a package containing a shared library is updated, and
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72 | if the name of the library changes, then any packages dynamically
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73 | linked to the library must be recompiled, to link against the
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74 | newer library. (Note that there is no correlation between the package
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75 | version and the name of the library.) For example, consider a package
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76 | foo-1.2.3 that installs a shared library with the name <filename
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77 | class='libraryfile'>libfoo.so.1</filename>. Suppose you upgrade the package to
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78 | a newer version foo-1.2.4 that installs a shared library with the name
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79 | <filename class='libraryfile'>libfoo.so.2</filename>. In this case, any
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80 | packages that are dynamically linked to <filename
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81 | class='libraryfile'>libfoo.so.1</filename> need to be recompiled to link
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82 | against <filename class='libraryfile'>libfoo.so.2</filename> in order to
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83 | use the new library version. You should not remove the old
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84 | libraries until all the dependent packages have been recompiled.</para>
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85 | </listitem>
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86 |
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87 | <listitem><para>If a package is (directly or indirectly) linked to both
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88 | the old and new names of a shared library (for example, the package
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89 | links to both <filename class='libraryfile'>libfoo.so.2</filename> and
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90 | <filename class='libraryfile'>libbar.so.1</filename>, while the latter
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91 | links to <filename class='libraryfile'>libfoo.so.3</filename>), the
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92 | package may malfunction because the different revisions of the shared
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93 | library present incompatible definitions for some symbol names. This can be
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94 | caused by recompiling some, but not all, of the packages linked to the
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95 | old shared library after the package providing the shared library is
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96 | upgraded. To avoid the issue, users will need to rebuild every package
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97 | linked to a shared library with an updated revision (e.g. libfoo.so.2 to
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98 | libfoo.so.3) as soon as possible.
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99 | </para></listitem>
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100 |
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101 | <listitem> <para>If a package containing a shared library is updated,
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102 | and the name of the library doesn't change, but the version number of the
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103 | library <emphasis role="bold">file</emphasis> decreases (for example,
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104 | the library is still named
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105 | <filename class='libraryfile'>libfoo.so.1</filename>,
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106 | but the name of the library file is changed from
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107 | <filename class='libraryfile'>libfoo.so.1.25</filename> to
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108 | <filename class='libraryfile'>libfoo.so.1.24</filename>),
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109 | you should remove the library file from the previously installed version
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110 | (<filename class='libraryfile'>libfoo.so.1.25</filename> in this case).
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111 | Otherwise, a <command>ldconfig</command> command (invoked by yourself from the command
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112 | line, or by the installation of some package) will reset the symlink
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113 | <filename class='libraryfile'>libfoo.so.1</filename> to point to
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114 | the old library file because it seems to be a <quote>newer</quote>
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115 | version; its version number is larger. This situation may arise if
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116 | you have to downgrade a package, or if the authors change the versioning
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117 | scheme for library files.</para> </listitem>
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118 |
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119 | <listitem><para>If a package containing a shared library is updated,
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120 | and the name of the library doesn't change, but a severe issue
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121 | (especially, a security vulnerability) is fixed, all running programs
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122 | linked to the shared library should be restarted. The following
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123 | command, run as <systemitem class="username">root</systemitem> after
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124 | the update is complete, will list which processes are using the old versions of those libraries
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125 | (replace <replaceable>libfoo</replaceable> with the name of the
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126 | library):</para>
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127 |
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128 | <screen role="nodump"><userinput>grep -l '<replaceable>libfoo</replaceable>.*deleted' /proc/*/maps | tr -cd 0-9\\n | xargs -r ps u</userinput></screen>
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129 |
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130 | <para>
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131 | If <application>OpenSSH</application> is being used to access
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132 | the system and it is linked to the updated library, you must
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133 | restart the <command>sshd</command> service, then logout, login again,
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134 | and run the preceding command again to confirm that nothing is still using the
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135 | deleted libraries.
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136 | </para>
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137 |
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138 | <para revision='systemd'>
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139 | If the <command>systemd</command> daemon (running as PID 1) is
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140 | linked to the updated library, you can restart it without rebooting
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141 | by running <command>systemctl daemon-reexec</command> as the
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142 | <systemitem class='username'>root</systemitem> user.
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143 | </para></listitem>
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144 |
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145 | <listitem>
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146 | <para>If an executable program or a shared library is overwritten, the processes
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147 | using the code or data in that program or library may crash. The
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148 | correct way to update a program or a shared library without causing
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149 | the process to crash is to remove it first, then install the new
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150 | version. The <command>install</command> command
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151 | provided by <application>coreutils</application> has already
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152 | implemented this, and most packages use that command to install binary files and
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153 | libraries. This means that you won't be troubled by this issue most of the time.
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154 | However, the install process of some packages (notably SpiderMonkey
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155 | in BLFS) just overwrites the file if it exists; this causes a crash. So
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156 | it's safer to save your work and close unneeded running processes
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157 | before updating a package.</para> <!-- binary is an adjective, not a noun. -->
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158 | </listitem>
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159 | </itemizedlist>
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160 |
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161 | </sect2>
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162 |
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163 | <sect2>
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164 | <title>Package Management Techniques</title>
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165 |
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166 | <para>The following are some common package management techniques. Before
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167 | making a decision on a package manager, do some research on the various
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168 | techniques, particularly the drawbacks of each particular scheme.</para>
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169 |
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170 | <sect3>
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171 | <title>It is All in My Head!</title>
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172 |
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173 | <para>Yes, this is a package management technique. Some folks do not
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174 | need a package manager because they know the packages intimately
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175 | and know which files are installed by each package. Some users also do not
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176 | need any package management because they plan on rebuilding the entire
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177 | system whenever a package is changed.</para>
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178 |
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179 | </sect3>
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180 |
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181 | <sect3>
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182 | <title>Install in Separate Directories</title>
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183 |
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184 | <para>This is a simplistic package management technique that does not need a
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185 | special program to manage the packages. Each package is installed in a
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186 | separate directory. For example, package foo-1.1 is installed in
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187 | <filename class='directory'>/opt/foo-1.1</filename>
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188 | and a symlink is made from <filename>/opt/foo</filename> to
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189 | <filename class='directory'>/opt/foo-1.1</filename>. When
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190 | a new version foo-1.2 comes along, it is installed in
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191 | <filename class='directory'>/opt/foo-1.2</filename> and the previous
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192 | symlink is replaced by a symlink to the new version.</para>
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193 |
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194 | <para>Environment variables such as <envar>PATH</envar>,
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195 | <envar>MANPATH</envar>, <envar>INFOPATH</envar>,
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196 | <envar>PKG_CONFIG_PATH</envar>, <envar>CPPFLAGS</envar>,
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197 | <envar>LDFLAGS</envar>, and the configuration file
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198 | <filename>/etc/ld.so.conf</filename> may need to be expanded to
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199 | include the corresponding subdirectories in
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200 | <filename class='directory'>/opt/foo-x.y</filename>.</para>
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201 |
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202 | <para>
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203 | This scheme is used by the BLFS book to install some very large
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204 | packages to make it easier to upgrade them. If you install more
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205 | than a few packages, this scheme becomes unmanageable. And some
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206 | packages (for example Linux API headers and Glibc) may not work well
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207 | with this scheme.
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208 | <emphasis role='bold'>Never use this scheme system-wide.</emphasis>
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209 | </para>
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210 | </sect3>
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211 |
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212 | <sect3>
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213 | <title>Symlink Style Package Management</title>
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214 |
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215 | <para>This is a variation of the previous package management technique.
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216 | Each package is installed as in the previous scheme. But instead of
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217 | making the symlink via a generic package name, each file is symlinked into the
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218 | <filename class='directory'>/usr</filename> hierarchy. This removes the
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219 | need to expand the environment variables. Though the symlinks can be
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220 | created by the user, many package managers use this approach, and
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221 | automate the creation of the symlinks. A few of the popular ones include Stow,
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222 | Epkg, Graft, and Depot.</para>
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223 |
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224 | <para>The installation script needs to be fooled, so the package thinks
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225 | it is installed in <filename class="directory">/usr</filename> though in
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226 | reality it is installed in the
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227 | <filename class="directory">/usr/pkg</filename> hierarchy. Installing in
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228 | this manner is not usually a trivial task. For example, suppose you
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229 | are installing a package libfoo-1.1. The following instructions may
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230 | not install the package properly:</para>
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231 |
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232 | <screen role="nodump"><userinput>./configure --prefix=/usr/pkg/libfoo/1.1
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233 | make
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234 | make install</userinput></screen>
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235 |
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236 | <para>The installation will work, but the dependent packages may not link
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237 | to libfoo as you would expect. If you compile a package that links against
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238 | libfoo, you may notice that it is linked to
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239 | <filename class='libraryfile'>/usr/pkg/libfoo/1.1/lib/libfoo.so.1</filename>
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240 | instead of <filename class='libraryfile'>/usr/lib/libfoo.so.1</filename>
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241 | as you would expect. The correct approach is to use the
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242 | <envar>DESTDIR</envar> variable to direct the installation. This
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243 | approach works as follows:</para>
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244 |
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245 | <screen role="nodump"><userinput>./configure --prefix=/usr
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246 | make
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247 | make DESTDIR=/usr/pkg/libfoo/1.1 install</userinput></screen>
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248 |
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249 | <para>Most packages support this approach, but there are some which do not.
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250 | For the non-compliant packages, you may either need to install the
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251 | package manually, or you may find that it is easier to install some problematic
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252 | packages into <filename class='directory'>/opt</filename>.</para>
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253 |
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254 | </sect3>
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255 |
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256 | <sect3>
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257 | <title>Timestamp Based</title>
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258 |
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259 | <para>In this technique, a file is timestamped before the installation of
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260 | the package. After the installation, a simple use of the
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261 | <command>find</command> command with the appropriate options can generate
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262 | a log of all the files installed after the timestamp file was created. A
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263 | package manager that uses this approach is install-log.</para>
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264 |
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265 | <para>Though this scheme has the advantage of being simple, it has two
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266 | drawbacks. If, during installation, the files are installed with any
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267 | timestamp other than the current time, those files will not be tracked by
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268 | the package manager. Also, this scheme can only be used when packages
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269 | are installed one at a time. The logs are not reliable if two packages are
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270 | installed simultaneously from two different consoles.</para>
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271 |
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272 | </sect3>
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273 |
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274 | <sect3>
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275 | <title>Tracing Installation Scripts</title>
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276 |
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277 | <para>In this approach, the commands that the installation scripts perform
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278 | are recorded. There are two techniques that one can use:</para>
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279 |
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280 | <para>The <envar>LD_PRELOAD</envar> environment variable can be set to
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281 | point to a library to be preloaded before installation. During
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282 | installation, this library tracks the packages that are being installed by
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283 | attaching itself to various executables such as <command>cp</command>,
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284 | <command>install</command>, <command>mv</command> and tracking the system
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285 | calls that modify the filesystem. For this approach to work, all the
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286 | executables need to be dynamically linked without the suid or sgid bit.
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287 | Preloading the library may cause some unwanted side-effects during
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288 | installation. Therefore, it's a good idea to perform some tests to
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289 | ensure that the package manager does not break anything, and that it logs all the
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290 | appropriate files.</para>
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291 |
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292 | <para>Another technique is to use <command>strace</command>, which
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293 | logs all the system calls made during the execution of the installation
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294 | scripts.</para>
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295 | </sect3>
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296 |
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297 | <sect3>
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298 | <title>Creating Package Archives</title>
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299 |
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300 | <para>In this scheme, the package installation is faked into a separate
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301 | tree as previously described in the symlink style package management section. After the
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302 | installation, a package archive is created using the installed files.
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303 | This archive is then used to install the package on the local
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304 | machine or even on other machines.</para>
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305 |
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306 | <para>This approach is used by most of the package managers found in the
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307 | commercial distributions. Examples of package managers that follow this
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308 | approach are RPM (which, incidentally, is required by the <ulink
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309 | url="https://refspecs.linuxfoundation.org/lsb.shtml">Linux
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310 | Standard Base Specification</ulink>), pkg-utils, Debian's apt, and
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311 | Gentoo's Portage system. A hint describing how to adopt this style of
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312 | package management for LFS systems is located at <ulink
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313 | url="&hints-root;fakeroot.txt"/>.</para>
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314 |
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315 | <para>The creation of package files that include dependency information is
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316 | complex, and beyond the scope of LFS.</para>
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317 |
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318 | <para>Slackware uses a <command>tar</command>-based system for package
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319 | archives. This system purposely does not handle package dependencies
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320 | as more complex package managers do. For details of Slackware package
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321 | management, see <ulink
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322 | url="https://www.slackbook.org/html/package-management.html"/>.</para>
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323 | </sect3>
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324 |
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325 | <sect3>
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326 | <title>User Based Management</title>
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327 |
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328 | <para>This scheme, unique to LFS, was devised by Matthias Benkmann, and is
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329 | available from the <ulink url="&hints-root;">Hints Project</ulink>. In
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330 | this scheme, each package is installed as a separate user into the
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331 | standard locations. Files belonging to a package are easily identified by
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332 | checking the user ID. The features and shortcomings of this approach are
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333 | too complex to describe in this section. For the details please see the
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334 | hint at <ulink url="&hints-root;more_control_and_pkg_man.txt"/>.</para>
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335 |
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336 | </sect3>
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337 |
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338 | </sect2>
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339 |
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340 | <sect2>
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341 | <title>Deploying LFS on Multiple Systems</title>
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342 |
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343 | <para>One of the advantages of an LFS system is that there are no files that
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344 | depend on the position of files on a disk system. Cloning an LFS build to
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345 | another computer with the same architecture as the base system is as
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346 | simple as using <command>tar</command> on the LFS partition that contains
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347 | the root directory (about 900MB uncompressed for a basic LFS build), copying
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348 | <!-- D. Bryant created LFS 11.2 in October 2022; 900MB is (roughly) the size of his rsync archive. -->
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349 | that file via network transfer or CD-ROM / USB stick to the new system, and expanding
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350 | it. After that, a few configuration files will have to be changed.
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351 | Configuration files that may need to be updated include:
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352 | <filename>/etc/hosts</filename>,
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353 | <filename>/etc/fstab</filename>,
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354 | <filename>/etc/passwd</filename>,
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355 | <filename>/etc/group</filename>,
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356 | <phrase revision="systemd">
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357 | <filename>/etc/shadow</filename>, and
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358 | <filename>/etc/ld.so.conf</filename>.
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359 | </phrase>
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360 | <phrase revision="sysv">
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361 | <filename>/etc/shadow</filename>,
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362 | <filename>/etc/ld.so.conf</filename>,
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363 | <filename>/etc/sysconfig/rc.site</filename>,
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364 | <filename>/etc/sysconfig/network</filename>, and
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365 | <filename>/etc/sysconfig/ifconfig.eth0</filename>.
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366 | </phrase>
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367 | </para>
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368 |
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369 | <para>A custom kernel may be needed for the new system, depending on
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370 | differences in system hardware and the original kernel
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371 | configuration.</para>
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372 |
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373 | <note><para>There have been some reports of issues when copying between
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374 | similar but not identical architectures. For instance, the instruction set
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375 | for an Intel system is not identical with the AMD processor's instructions, and later
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376 | versions of some processors may provide instructions that are unavailable with
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377 | earlier versions.</para></note>
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378 |
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379 | <para>Finally, the new system has to be made bootable via <xref
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380 | linkend="ch-bootable-grub"/>.</para>
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381 |
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382 | </sect2>
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383 |
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384 | </sect1>
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