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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 CLFS Book. A |
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14 | Package Manager allows tracking the installation of files making it easy to |
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15 | remove and upgrade packages. Before you begin to wonder, NO—this section |
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16 | will not talk about nor recommend any particular package manager. What it |
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17 | provides is a roundup of the more popular techniques and how they work. The |
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18 | perfect package manager for you may be among these techniques or may be a |
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19 | combination of two or more of these techniques. This section briefly mentions |
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20 | issues that may arise when upgrading packages.</para> |
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21 | |
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22 | <para>Some reasons why no specific package manager is recommended in |
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23 | CLFS or CBLFS include:</para> |
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24 | |
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25 | <itemizedlist> |
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26 | <listitem> |
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27 | <para>Dealing with package management takes the focus away from the goals |
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28 | of these books—teaching how a Linux system is built.</para> |
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29 | </listitem> |
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30 | |
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31 | <listitem> |
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32 | <para>There are multiple solutions for package management, each having |
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33 | its strengths and drawbacks. Including one that satisfies all audiences |
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34 | is difficult.</para> |
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35 | </listitem> |
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36 | </itemizedlist> |
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37 | |
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38 | <para>There are some hints written on the topic of package management. Visit |
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39 | the <ulink url="&hints-root;">Hints subproject</ulink> and see if one of them |
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40 | fits your need.</para> |
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41 | |
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42 | <sect2> |
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43 | <title>Upgrade Issues</title> |
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44 | |
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45 | <para>A Package Manager makes it easy to upgrade to newer versions when they |
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46 | are released. Generally the instructions in CLFS and CBLFS can be |
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47 | used to upgrade to the newer versions. Here are some points that you should |
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48 | be aware of when upgrading packages, especially on a running system.</para> |
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49 | |
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50 | <itemizedlist> |
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51 | <listitem> |
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52 | <para>If one of the toolchain packages (Glibc, GCC or Binutils) needs |
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53 | to be upgraded to a newer minor version, it is safer to |
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54 | rebuild CLFS. Though you <emphasis>may</emphasis> be able to get by |
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55 | rebuilding all the packages in their dependency order, we do not |
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56 | recommend it. For example, if glibc-2.2.x needs to be updated to |
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57 | glibc-2.3.x, it is safer to rebuild. For micro version updates, a |
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58 | simple reinstallation usually works, but is not guaranteed. For |
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59 | example, upgrading from glibc-2.3.4 to glibc-2.3.5 will not |
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60 | usually cause any problems.</para> |
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61 | </listitem> |
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62 | |
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63 | <listitem> |
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64 | <para>If a package containing a shared library is updated, and if the |
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65 | name of the library changes, then all the packages dynamically linked |
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66 | to the library need to be recompiled to link against the newer library. |
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67 | (Note that there is no correlation between the package version and the |
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68 | name of the library.) For example, consider a package foo-1.2.3 that |
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69 | installs a shared library with name |
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70 | <filename class='libraryfile'>libfoo.so.1</filename>. Say you upgrade |
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71 | the package to a newer version foo-1.2.4 that installs a shared library |
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72 | with name <filename class='libraryfile'>libfoo.so.2</filename>. In this |
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73 | case, all packages that are dynamically linked to |
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74 | <filename class='libraryfile'>libfoo.so.1</filename> need to be |
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75 | recompiled to link against |
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76 | <filename class='libraryfile'>libfoo.so.2</filename>. Note that you |
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77 | should not remove the previous libraries until the dependent packages |
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78 | are recompiled.</para> |
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79 | </listitem> |
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80 | |
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81 | <listitem> |
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82 | <para>If you are upgrading a running system, be on the lookout for |
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83 | packages that use <command>cp</command> instead of |
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84 | <command>install</command> to install files. The latter command is |
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85 | usually safer if the executable or library is already loaded in memory. |
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86 | </para> |
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87 | </listitem> |
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88 | </itemizedlist> |
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89 | |
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90 | </sect2> |
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91 | |
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92 | <sect2> |
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93 | <title>Package Management Techniques</title> |
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94 | |
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95 | <para>The following are some common package management techniques. Before |
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96 | making a decision on a package manager, do some research on the various |
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97 | techniques, particularly the drawbacks of the particular scheme.</para> |
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98 | |
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99 | <sect3> |
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100 | <title>It is All in My Head!</title> |
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101 | |
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102 | <para>Yes, this is a package management technique. Some folks do not find |
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103 | the need for a package manager because they know the packages intimately |
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104 | and know what files are installed by each package. Some users also do not |
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105 | need any package management because they plan on rebuilding the entire |
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106 | system when a package is changed.</para> |
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107 | |
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108 | </sect3> |
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109 | |
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110 | <sect3> |
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111 | <title>Install in Separate Directories</title> |
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112 | |
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113 | <para>This is a simplistic package management that does not need any extra |
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114 | package to manage the installations. Each package is installed in a |
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115 | separate directory. For example, package foo-1.1 is installed in |
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116 | <filename class='directory'>/usr/pkg/foo-1.1</filename> |
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117 | and a symlink is made from <filename>/usr/pkg/foo</filename> to |
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118 | <filename class='directory'>/usr/pkg/foo-1.1</filename>. When installing |
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119 | a new version foo-1.2, it is installed in |
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120 | <filename class='directory'>/usr/pkg/foo-1.2</filename> and the previous |
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121 | symlink is replaced by a symlink to the new version.</para> |
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122 | |
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123 | <para>Environment variables such as <envar>PATH</envar>, |
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124 | <envar>LD_LIBRARY_PATH</envar>, <envar>MANPATH</envar>, |
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125 | <envar>INFOPATH</envar> and <envar>CPPFLAGS</envar> need to be expanded to |
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126 | include <filename>/usr/pkg/foo</filename>. For more than a few packages, |
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127 | this scheme becomes unmanageable.</para> |
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128 | |
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129 | </sect3> |
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130 | |
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131 | <sect3> |
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132 | <title>Symlink Style Package Management</title> |
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133 | |
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134 | <para>This is a variation of the previous package management technique. |
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135 | Each package is installed similar to the previous scheme. But instead of |
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136 | making the symlink, each file is symlinked into the |
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137 | <filename class='directory'>/usr</filename> hierarchy. This removes the |
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138 | need to expand the environment variables. Though the symlinks can be |
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139 | created by the user to automate the creation, many package managers have |
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140 | been written using this approach. A few of the popular ones include Stow, |
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141 | Epkg, Graft, and Depot.</para> |
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142 | |
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143 | <para>The installation needs to be faked, so that the package thinks that |
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144 | it is installed in <filename class="directory">/usr</filename> though in |
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145 | reality it is installed in the |
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146 | <filename class="directory">/usr/pkg</filename> hierarchy. Installing in |
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147 | this manner is not usually a trivial task. For example, consider that you |
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148 | are installing a package libfoo-1.1. The following instructions may |
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149 | not install the package properly:</para> |
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150 | |
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151 | <screen role="nodump"><userinput>./configure --prefix=/usr/pkg/libfoo/1.1 |
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152 | make |
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153 | make install</userinput></screen> |
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154 | |
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155 | <para>The installation will work, but the dependent packages may not link |
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156 | to libfoo as you would expect. If you compile a package that links against |
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157 | libfoo, you may notice that it is linked to |
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158 | <filename class='libraryfile'>/usr/pkg/libfoo/1.1/lib/libfoo.so.1</filename> |
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159 | instead of <filename class='libraryfile'>/usr/lib/libfoo.so.1</filename> |
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160 | as you would expect. The correct approach is to use the |
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161 | <envar>DESTDIR</envar> strategy to fake installation of the package. This |
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162 | approach works as follows:</para> |
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163 | |
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164 | <screen role="nodump"><userinput>./configure --prefix=/usr |
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165 | make |
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166 | make DESTDIR=/usr/pkg/libfoo/1.1 install</userinput></screen> |
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167 | |
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168 | <para>Most packages support this approach, but there are some which do not. |
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169 | For the non-compliant packages, you may either need to manually install the |
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170 | package, or you may find that it is easier to install some problematic |
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171 | packages into <filename class='directory'>/opt</filename>.</para> |
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172 | |
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173 | </sect3> |
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174 | |
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175 | <sect3> |
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176 | <title>Timestamp Based</title> |
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177 | |
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178 | <para>In this technique, a file is timestamped before the installation of |
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179 | the package. After the installation, a simple use of the |
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180 | <command>find</command> command with the appropriate options can generate |
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181 | a log of all the files installed after the timestamp file was created. A |
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182 | package manager written with this approach is install-log.</para> |
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183 | |
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184 | <para>Though this scheme has the advantage of being simple, it has two |
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185 | drawbacks. If, during installation, the files are installed with any |
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186 | timestamp other than the current time, those files will not be tracked by |
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187 | the package manager. Also, this scheme can only be used when one package |
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188 | is installed at a time. The logs are not reliable if two packages are |
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189 | being installed on two different consoles.</para> |
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190 | |
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191 | </sect3> |
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192 | |
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193 | <sect3> |
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194 | <title>LD_PRELOAD Based</title> |
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195 | |
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196 | <para>In this approach, a library is preloaded before installation. During |
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197 | installation, this library tracks the packages that are being installed by |
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198 | attaching itself to various executables such as <command>cp</command>, |
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199 | <command>install</command>, <command>mv</command> and tracking the system |
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200 | calls that modify the filesystem. For this approach to work, all the |
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201 | executables need to be dynamically linked without the suid or sgid bit. |
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202 | Preloading the library may cause some unwanted side-effects during |
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203 | installation. Therefore, it is advised that one performs some tests to |
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204 | ensure that the package manager does not break anything and logs all the |
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205 | appropriate files.</para> |
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206 | |
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207 | </sect3> |
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208 | |
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209 | <sect3> |
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210 | <title>Creating Package Archives</title> |
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211 | |
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212 | <para>In this scheme, the package installation is faked into a separate |
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213 | tree as described in the Symlink style package management. After the |
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214 | installation, a package archive is created using the installed files. |
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215 | This archive is then used to install the package either on the local |
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216 | machine or can even be used to install the package on other machines.</para> |
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217 | |
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218 | <para>This approach is used by most of the package managers found in the |
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219 | commercial distributions. Examples of package managers that follow this |
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220 | approach are RPM (which, incidentally, is required by the <ulink |
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221 | url="http://refspecs.linuxfoundation.org/lsb.shtml">Linux |
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222 | Standard Base Specification</ulink>), pkg-utils, Debian's apt, and |
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223 | Gentoo's Portage system. A hint describing how to adopt this style of |
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224 | package management for CLFS systems is located at <ulink |
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225 | url="&hints-root;Fakeroot"/>.</para> |
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226 | |
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227 | </sect3> |
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228 | |
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229 | </sect2> |
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230 | |
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231 | </sect1> |
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