[4122007] | 1 | <?xml version="1.0" encoding="ISO-8859-1"?>
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[ff769b8c] | 2 | <!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd" [
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[4122007] | 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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[3d760b6] | 8 | <sect1 id="intro-important-pkgmgt">
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[1f24363] | 9 | <?dbhtml filename="pkgmgt.html"?>
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| 10 |
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| 11 | <sect1info>
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| 12 | <othername>$LastChangedBy$</othername>
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| 13 | <date>$Date$</date>
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| 14 | </sect1info>
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| 15 |
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| 16 | <title>Package Management</title>
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| 17 |
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| 18 | <para>Package Management is an often requested addition
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| 19 | to the LFS Book. A Package Manager allows tracking
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| 20 | the installation of files making it easy to remove and upgrade packages.
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| 21 | And before you begin to wonder, NO—this section does not talk about any
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| 22 | particular package manager, nor does it recommend one. What it provides is
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| 23 | a roundup of the more popular techniques and how they work. The perfect
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| 24 | package manager for you may be among these techniques or may be a combination
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| 25 | of two or more of these techniques. This section briefly mentions
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| 26 | issues that may arise when upgrading packages.</para>
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| 27 |
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| 28 | <para>Some reasons why no package manager is mentioned in LFS
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| 29 | or BLFS:</para>
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| 30 |
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| 31 | <itemizedlist>
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| 32 | <listitem>
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| 33 | <para>Dealing with package management takes the focus away from
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| 34 | the goals of these books—teaching how a Linux system is built.</para>
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| 35 | </listitem>
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| 36 | <listitem>
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| 37 | <para>There are multiple solutions for package management, each having
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| 38 | its strengths and drawbacks. Including one that satifies all audiences is
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| 39 | difficult.</para>
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| 40 | </listitem>
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| 41 | </itemizedlist>
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| 42 |
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| 43 | <para>There are some hints written on the topic of package management. Visit
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| 44 | the <ulink url="http://www.linuxfromscratch.org/hints/">Hints subproject</ulink>
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| 45 | to find if one of them fits your need.</para>
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| 46 |
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| 47 | <sect2>
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| 48 | <title>Upgrade Issues</title>
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| 49 |
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| 50 | <para>A Package Manager makes it easy to upgrade to newer versions when
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| 51 | they are released. Generally the instructions in the LFS and BLFS Book can be
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| 52 | used to upgrade to the newer versions. Here are some points that you should
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| 53 | be aware of when upgrading packages, especially on a running system.</para>
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| 54 |
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| 55 | <itemizedlist>
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| 56 | <listitem>
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| 57 | <para>If one of the toolchain package (glibc, gcc,
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| 58 | binutils) needs to be upgraded to a newer minor vesion, it is safer to rebuild
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| 59 | LFS. Though you <emphasis>may</emphasis> be able to get by
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| 60 | rebuilding all the packages in their dependency order. We do not recommend it.
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| 61 | For example, if glibc-2.2.x needs to be updated to glibc-2.3.x, it is safer
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| 62 | to rebuild. For micro version updates, a simple reinstallation usually works, but
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| 63 | is not guaranteed. For example, upgrading from glibc-2.3.1 to glibc-2.3.2 will not
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| 64 | usually cause any problems.</para>
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| 65 | </listitem>
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| 66 | <listitem>
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| 67 | <para>If a package containing a shared library is updated, and if the
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| 68 | name of the library changes, then all the packages dynamically linked to the
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| 69 | library need to be recompiled to link against the newer library. (Note that there
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| 70 | is no corelation between the package version and the name of the library.) For
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| 71 | example, consider a package foo-1.2.3 that installs a shared library with name
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| 72 | <filename>libfoo.so.1</filename>. Say you upgrade the package to a newer version
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| 73 | foo-1.2.4 that installs a shared library with name <filename>libfoo.so.2</filename>.
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| 74 | In this case, all packages that are dynamically linked to <filename>libfoo.so.1</filename>
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| 75 | need to be recompiled to link against <filename>libfoo.so.2</filename>. Note that
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| 76 | you should not remove the previous libraries till the dependent packages are
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| 77 | recompiled.</para>
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| 78 | </listitem>
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| 79 | <listitem>
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| 80 | <para>If you are upgrading a running system, be on the lookout for packages
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| 81 | that use <command>cp</command> instead of <command>install</command>
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| 82 | to install files. The latter command is usually safer if the executable or library
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| 83 | is already loaded in memory.</para>
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| 84 | </listitem>
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| 85 | </itemizedlist>
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| 86 |
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| 87 | </sect2>
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| 88 |
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| 89 | <sect2>
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| 90 | <title>Package Management Techniques</title>
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| 91 |
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| 92 | <para>The following are some common package management techniques. Before
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| 93 | making a decision on a package manager, do a research on the various
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| 94 | techniques, particularly the drawbacks of the particular scheme.</para>
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| 95 |
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| 96 | <sect3>
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| 97 | <title>It is All in My Head!</title>
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| 98 |
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| 99 | <para>Yes, this is a package management technique. Some folks do not find the
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| 100 | need for a package manager because they know the packages intimately and know
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| 101 | what files are installed by each package. Some users also do not need any
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| 102 | package management because they plan on rebuilding the entire system
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| 103 | when a package is changed.</para>
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| 104 |
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| 105 | </sect3>
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| 106 |
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| 107 | <sect3>
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| 108 | <title>Install in Separate Directories</title>
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| 109 |
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| 110 | <para>This is a simplistic package management that does not need any extra package
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| 111 | to manage the installations. Each package is installed in a separate directory.
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| 112 | For example, package foo-1.1 is installed in <filename>/usr/pkg/foo-1.1</filename>
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| 113 | and a symlink is made from <filename>/usr/pkg/foo</filename> to
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| 114 | <filename>/usr/pkg/foo-1.1</filename>. When installing a new version foo-1.2,
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| 115 | it is installed in <filename>/usr/pkg/foo-1.2</filename> and the previous
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| 116 | symlink is replaced by a symlink to the new vesion.</para>
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| 117 |
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| 118 | <para>The environment variables such as those
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| 119 | mentioned in <xref linkend="intro-important-beyond"/> need to be expanded to
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| 120 | include <filename>/usr/pkg/foo</filename>. For more than a few packages,
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| 121 | this scheme becomes unmanageable.</para>
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| 122 |
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| 123 | </sect3>
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| 124 |
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| 125 | <sect3>
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| 126 | <title>Symlink Style Package Management</title>
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| 127 |
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| 128 | <para>This is a variation of the previous package management technique. Each package
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| 129 | is installed similar to the previous scheme. But instead of making the symlink,
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| 130 | each file is symlinked into <filename>/usr</filename> hierarchy. This removes the need
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| 131 | to expand the environment variables. Though the symlinks can be created by the user,
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| 132 | to automate the creation, many package managers have been written on this approach.
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| 133 | A few of the popular ones are Stow, Epkg, Graft, and Depot.</para>
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| 134 |
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| 135 | <para>The installation needs to be faked, so that the package thinks that it is
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| 136 | installed in <filename class="directory">/usr</filename> though in reality it is
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| 137 | installed in <filename class="directory">/usr/pkg</filename> hierarchy.
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| 138 | Installing in this manner is not usually a trivial task. For example, consider
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| 139 | that you are installing a package libfoo-1.1. The following instructions may
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| 140 | not install the package properly:</para>
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| 141 |
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| 142 | <screen><userinput>./configure --prefix=/usr/pkg/libfoo/1.1
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[20828163] | 143 | make
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[1f24363] | 144 | make install</userinput></screen>
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[3d760b6] | 145 |
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[1f24363] | 146 | <para>The installation will work, but the dependent packages may not link to
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| 147 | libfoo as you would expect. If you compile a package that links against libfoo,
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| 148 | you may notice that it is linked to <filename>/usr/pkg/libfoo/1.1/lib/libfoo.so.1</filename>
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| 149 | instead of <filename>/usr/lib/libfoo.so.1</filename> as you would expect. The correct
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| 150 | approach is to use <envar>DESTDIR</envar> strategy to fake installation of the package.
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| 151 | This approach works as follows:</para>
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[3d760b6] | 152 |
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[1f24363] | 153 | <screen><userinput>./configure --prefix=/usr
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[20828163] | 154 | make
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[1f24363] | 155 | make DESTDIR=/usr/pkg/libfoo/1.1 install</userinput></screen>
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[3d760b6] | 156 |
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[1f24363] | 157 | <para>Most of the packages do support this approach, but there are some which do not.
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| 158 | For the non-compliant packages, you may either need to manually install the package,
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| 159 | or you may find that it is easier to install some problematic packages into
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| 160 | <filename>/opt</filename>.</para>
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[3d760b6] | 161 |
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[1f24363] | 162 | </sect3>
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[3d760b6] | 163 |
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[1f24363] | 164 | <sect3>
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| 165 | <title>Timestamp Based</title>
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[3d760b6] | 166 |
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[1f24363] | 167 | <para>In this technique, a file is timestamped before the installation of the package.
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| 168 | After the installation, a simple use of the <command>find</command> command with the
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| 169 | appropriate options can generate a log of all the files installed after the timestamp
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| 170 | file was created. A package manager written with this approach is install-log.</para>
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[3d760b6] | 171 |
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[1f24363] | 172 | <para>Though this scheme has the advantage of being simple, it has two drawbacks.
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| 173 | If during installation, the files are installed with any timestamp other than the
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| 174 | current time, those files will not be tracked by the package manager. Also, this
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| 175 | scheme can only be used when one package is installed at a time. The logs are not
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| 176 | reliable if two packages are being installed on two different consoles.</para>
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[3d760b6] | 177 |
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[1f24363] | 178 | </sect3>
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[3d760b6] | 179 |
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[1f24363] | 180 | <sect3>
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| 181 | <title>LD_PRELOAD Based</title>
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[3d760b6] | 182 |
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[1f24363] | 183 | <para>In this approach, a library is preloaded before installation. During
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| 184 | installation, this library tracks the packages that are being installed by
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| 185 | attaching itself to various executables such as <command>cp</command>,
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| 186 | <command>install</command>, <command>mv</command> and tracking the system
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| 187 | calls that modify the filesystem. For this approach to work, all the executables
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| 188 | need to be dymanically linked without the suid or sgid bit. Preloading the
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| 189 | library may cause some unwanted side-effects during installation. Therefore,
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| 190 | do perform some tests to ensure that the package manager does not break
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| 191 | anything and logs all the appropriate files.</para>
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[3d760b6] | 192 |
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[1f24363] | 193 | </sect3>
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[3d760b6] | 194 |
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[1f24363] | 195 | <sect3>
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| 196 | <title>Creating Package Archives</title>
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[3d760b6] | 197 |
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[1f24363] | 198 | <para>In this scheme, the package installation is faked into a separate
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| 199 | tree as described in the Symlink style package management. After the
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| 200 | installation, a package archive is created using the installed files.
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| 201 | This archive is then used to install the package either on the local
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| 202 | machine or can even be used to install the package on other machines.</para>
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[3d760b6] | 203 |
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[1f24363] | 204 | <para>This approach is used by most of the package managers found in the
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| 205 | commercial distributions. Examples of package managers that follow this
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| 206 | approach are RPM, pkg-utils, Debian's apt, and Gentoo's Portage system.</para>
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[3d760b6] | 207 |
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[1f24363] | 208 | </sect3>
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[3d760b6] | 209 |
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[1f24363] | 210 | <sect3>
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| 211 | <title>User Based Management</title>
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[3d760b6] | 212 |
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[1f24363] | 213 | <para>This scheme, that is unique to LFS, was devised by Matthias Benkmann,
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| 214 | and is available from the <ulink url="http://www.linuxfromscratch.org/hints/">Hints
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| 215 | Project</ulink>. In this scheme, each package is installed as a separate user
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| 216 | into the standard locations. Files belonging to a package are easily identified
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| 217 | by checking the user id. The features and shortcomings of this approach are
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| 218 | too complex to describe in this section. For the details please see the hint at <ulink
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| 219 | url="http://www.linuxfromscratch.org/hints/downloads/files/more_control_and_pkg_man.txt"/>.</para>
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[3d760b6] | 220 |
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[1f24363] | 221 | </sect3>
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[3d760b6] | 222 |
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[1f24363] | 223 | </sect2>
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[3d760b6] | 224 |
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| 225 | </sect1>
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