source: introduction/important/pkgmgt.xml@ 1f24363

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<sect1 id="intro-important-pkgmgt">
  <?dbhtml filename="pkgmgt.html"?>

  <sect1info>
    <othername>$LastChangedBy$</othername>
    <date>$Date$</date>
  </sect1info>

  <title>Package Management</title>

  <para>Package Management is an often requested addition
  to the LFS Book. A Package Manager allows tracking
  the installation of files making it easy to remove and upgrade packages.
  And before you begin to wonder, NO&mdash;this section does not talk about any
  particular package manager, nor does it recommend one. What it provides is
  a roundup of the more popular techniques and how they work. The perfect
  package manager for you may be among these techniques or may be a combination
  of two or more of these techniques. This section briefly mentions
  issues that may arise when upgrading packages.</para>

  <para>Some reasons why no package manager is mentioned in LFS
  or BLFS:</para>

  <itemizedlist>
    <listitem>
      <para>Dealing with package management takes the focus away from
      the goals of these books&mdash;teaching how a Linux system is built.</para>
    </listitem>
    <listitem>
      <para>There are multiple solutions for package management, each having
      its strengths and drawbacks. Including one that satifies all audiences is
      difficult.</para>
    </listitem>
  </itemizedlist>

  <para>There are some hints written on the topic of package management. Visit
  the <ulink url="http://www.linuxfromscratch.org/hints/">Hints subproject</ulink>
  to find if one of them fits your need.</para>

  <sect2>
    <title>Upgrade Issues</title>

    <para>A Package Manager makes it easy to upgrade to newer versions when 
    they are released. Generally the instructions in the LFS and BLFS Book can be 
    used to upgrade to the newer versions. Here are some points that you should 
    be aware of when upgrading packages, especially on a running system.</para>

    <itemizedlist>
      <listitem>
        <para>If one of the toolchain package (glibc, gcc,
        binutils) needs to be upgraded to a newer minor vesion, it is safer to rebuild
        LFS. Though you <emphasis>may</emphasis> be able to get by
        rebuilding all the packages in their dependency order. We do not recommend it.
        For example, if glibc-2.2.x needs to be updated to glibc-2.3.x, it is safer
        to rebuild. For micro version updates, a simple reinstallation usually works, but
        is not guaranteed. For example, upgrading from glibc-2.3.1 to glibc-2.3.2 will not
        usually cause any problems.</para>
      </listitem>
      <listitem>
        <para>If a package containing a shared library is updated, and if the
        name of the library changes, then all the packages dynamically linked to the
        library need to be recompiled to link against the newer library. (Note that there
        is no corelation between the package version and the name of the library.) For
        example, consider a package foo-1.2.3 that installs a shared library with name
        <filename>libfoo.so.1</filename>. Say you upgrade the package to a newer version
        foo-1.2.4 that installs a shared library with name <filename>libfoo.so.2</filename>.
        In this case, all packages that are dynamically linked to <filename>libfoo.so.1</filename>
        need to be recompiled to link against <filename>libfoo.so.2</filename>. Note that
        you should not remove the previous libraries till the dependent packages are
        recompiled.</para>
      </listitem>
      <listitem>
        <para>If you are upgrading a running system, be on the lookout for packages 
        that use <command>cp</command> instead of <command>install</command>
        to install files. The latter command is usually safer if the executable or library
        is already loaded in memory.</para>
      </listitem>
    </itemizedlist>

  </sect2>

  <sect2>
    <title>Package Management Techniques</title>

    <para>The following are some common package management techniques. Before
    making a decision on a package manager, do a research on the various
    techniques, particularly the drawbacks of the particular scheme.</para>

    <sect3>
      <title>It is All in My Head!</title>

      <para>Yes, this is a package management technique. Some folks do not find the
      need for a package manager because they know the packages intimately and know
      what files are installed by each package. Some users also do not need any
      package management because they plan on rebuilding the entire system
      when a package is changed.</para>

    </sect3>

    <sect3>
      <title>Install in Separate Directories</title>

      <para>This is a simplistic package management that does not need any extra package
      to manage the installations. Each package is installed in a separate directory.
      For example, package foo-1.1 is installed in <filename>/usr/pkg/foo-1.1</filename>
      and a symlink is made from <filename>/usr/pkg/foo</filename> to
      <filename>/usr/pkg/foo-1.1</filename>. When installing a new version foo-1.2,
      it is installed in <filename>/usr/pkg/foo-1.2</filename> and the previous
      symlink is replaced by a symlink to the new vesion.</para>

      <para>The environment variables such as those
      mentioned in <xref linkend="intro-important-beyond"/> need to be expanded to
      include <filename>/usr/pkg/foo</filename>. For more than a few packages,
      this scheme becomes unmanageable.</para>

    </sect3>

    <sect3>
      <title>Symlink Style Package Management</title>

      <para>This is a variation of the previous package management technique. Each package
      is installed similar to the previous scheme. But instead of making the symlink,
      each file is symlinked into <filename>/usr</filename> hierarchy. This removes the need
      to expand the environment variables. Though the symlinks can be created by the user,
      to automate the creation, many package managers have been written on this approach.
      A few of the popular ones are Stow, Epkg, Graft, and Depot.</para>

      <para>The installation needs to be faked, so that the package thinks that it is
      installed in <filename class="directory">/usr</filename> though in reality it is 
      installed in <filename class="directory">/usr/pkg</filename> hierarchy. 
      Installing in this manner is not usually a trivial task. For example, consider 
      that you are installing a package libfoo-1.1. The following instructions may 
      not install the package properly:</para>

<screen><userinput>./configure --prefix=/usr/pkg/libfoo/1.1 
make
make install</userinput></screen>

      <para>The installation will work, but the dependent packages may not link to
      libfoo as you would expect. If you compile a package that links against libfoo,
      you may notice that it is linked to <filename>/usr/pkg/libfoo/1.1/lib/libfoo.so.1</filename>
      instead of <filename>/usr/lib/libfoo.so.1</filename> as you would expect. The correct
      approach is to use <envar>DESTDIR</envar> strategy to fake installation of the package.
      This approach works as follows:</para>

<screen><userinput>./configure --prefix=/usr
make
make DESTDIR=/usr/pkg/libfoo/1.1 install</userinput></screen>

      <para>Most of the packages do support this approach, but there are some which do not.
      For the non-compliant packages, you may either need to manually install the package,
      or you may find that it is easier to install some problematic packages into
      <filename>/opt</filename>.</para>

    </sect3>

    <sect3>
      <title>Timestamp Based</title>

      <para>In this technique, a file is timestamped before the installation of the package.
      After the installation, a simple use of the <command>find</command> command with the
      appropriate options can generate a log of all the files installed after the timestamp
      file was created. A package manager written with this approach is install-log.</para>

      <para>Though this scheme has the advantage of being simple, it has two drawbacks.
      If during installation, the files are installed with any timestamp other than the
      current time, those files will not be tracked by the package manager. Also, this
      scheme can only be used when one package is installed at a time. The logs are not
      reliable if two packages are being installed on two different consoles.</para>

    </sect3>

    <sect3>
      <title>LD_PRELOAD Based</title>

      <para>In this approach, a library is preloaded before installation. During
      installation, this library tracks the packages that are being installed by
      attaching itself to various executables such as <command>cp</command>,
      <command>install</command>, <command>mv</command> and tracking the system
      calls that modify the filesystem. For this approach to work, all the executables
      need to be dymanically linked without the suid or sgid bit. Preloading the
      library may cause some unwanted side-effects during installation. Therefore,
      do perform some tests to ensure that the package manager does not break
      anything and logs all the appropriate files.</para>

    </sect3>

    <sect3>
      <title>Creating Package Archives</title>

      <para>In this scheme, the package installation is faked into a separate
      tree as described in the Symlink style package management. After the
      installation, a package archive is created using the installed files.
      This archive is then used to install the package either on the local
      machine or can even be used to install the package on other machines.</para>

      <para>This approach is used by most of the package managers found in the
      commercial distributions. Examples of package managers that follow this
      approach are RPM, pkg-utils, Debian's apt, and Gentoo's Portage system.</para>

    </sect3>

    <sect3>
      <title>User Based Management</title>

      <para>This scheme, that is unique to LFS, was devised by Matthias Benkmann, 
      and is available from the <ulink url="http://www.linuxfromscratch.org/hints/">Hints 
      Project</ulink>. In this scheme, each package is installed as a separate user 
      into the standard locations. Files belonging to a package are easily identified 
      by checking the user id. The features and shortcomings of this approach are 
      too complex to describe in this section. For the details please see the hint at <ulink
      url="http://www.linuxfromscratch.org/hints/downloads/files/more_control_and_pkg_man.txt"/>.</para>

    </sect3>

  </sect2>

</sect1>