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<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY % general-entities SYSTEM "../general.ent">
%general-entities;
]>
<sect1 id="ch-system-pkgmgt">
<?dbhtml filename="pkgmgt.html"?>
<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. Before you begin to wonder, NO—this section
will not talk about nor recommend any particular package manager. 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
include:</para>
<itemizedlist>
<listitem>
<para>Dealing with package management takes the focus away from the goals
of these books—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 satisfies all audiences
is difficult.</para>
</listitem>
</itemizedlist>
<para>There are some hints written on the topic of package management. Visit
the <ulink url="&hints-root;">Hints subproject</ulink> and see 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 packages (Glibc, GCC or Binutils) needs
to be upgraded to a newer minor version, 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-2.3.4
to glibc-2.3.5 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 correlation 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 class='libraryfile'>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 class='libraryfile'>libfoo.so.2</filename>. In this
case, all packages that are dynamically linked to
<filename class='libraryfile'>libfoo.so.1</filename> need to be
recompiled to link against
<filename class='libraryfile'>libfoo.so.2</filename>. Note that you
should not remove the previous libraries until the dependent packages
are recompiled.</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 some 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 class='directory'>/usr/pkg/foo-1.1</filename>
and a symlink is made from <filename>/usr/pkg/foo</filename> to
<filename class='directory'>/usr/pkg/foo-1.1</filename>. When installing
a new version foo-1.2, it is installed in
<filename class='directory'>/usr/pkg/foo-1.2</filename> and the previous
symlink is replaced by a symlink to the new version.</para>
<para>Environment variables such as <envar>PATH</envar>,
<envar>LD_LIBRARY_PATH</envar>, <envar>MANPATH</envar>,
<envar>INFOPATH</envar> and <envar>CPPFLAGS</envar> 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 the
<filename class='directory'>/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 using this approach. A few of the popular ones include 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 the
<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 role="nodump"><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 class='libraryfile'>/usr/pkg/libfoo/1.1/lib/libfoo.so.1</filename>
instead of <filename class='libraryfile'>/usr/lib/libfoo.so.1</filename>
as you would expect. The correct approach is to use the
<envar>DESTDIR</envar> strategy to fake installation of the package. This
approach works as follows:</para>
<screen role="nodump"><userinput>./configure --prefix=/usr
make
make DESTDIR=/usr/pkg/libfoo/1.1 install</userinput></screen>
<para>Most packages 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 class='directory'>/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 dynamically linked without the suid or sgid bit.
Preloading the library may cause some unwanted side-effects during
installation. Therefore, it is advised that one performs 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 (which, incidentally, is required by the <ulink
url="http://lsbbook.gforge.freestandards.org/package.html#RPM">Linux
Standard Base Specification</ulink>), pkg-utils, Debian's apt, and
Gentoo's Portage system. A hint describing how to adopt this style of
package management for LFS systems is located at <ulink
url="&hints-root;fakeroot.txt"/>.</para>
</sect3>
<sect3>
<title>User Based Management</title>
<para>This scheme, unique to LFS, was devised by Matthias Benkmann, and is
available from the <ulink url="&hints-root;">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="&hints-root;more_control_and_pkg_man.txt"/>.</para>
</sect3>
</sect2>
</sect1>
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