~linaro-maintainers/live-build/linaro-live-build-3

<h2><a name="s-depends"></a>7.9 What is meant by saying that a package Depends, Recommends, Suggests, Conflicts, Replaces or Provides another package?</h2>

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The Debian package system has a range of package "dependencies" which

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are designed to indicate (in a single flag) the level at which Program A can

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operate independently of the existence of Program B on a given system:

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<ul>

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<li>

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Package A depends on Package B if B absolutely must be installed in

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order to run A. In some cases, A depends not only on B, but on a version of B.

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In this case, the version dependency is usually a lower limit, in the sense

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that A depends on any version of B more recent than some specified version.

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</li>

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</ul>

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<ul>

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<li>

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Package A recommends Package B, if the package maintainer judges that

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most users would not want A without also having the functionality provided by

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</li>

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</ul>

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<ul>

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<li>

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Package A suggests Package B if B contains files that are related to

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(and usually enhance) the functionality of A.

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</li>

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</ul>

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<ul>

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<li>

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Package A conflicts with Package B when A will not operate if B is

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installed on the system. Most often, conflicts are cases where A contains

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files which are an improvement over those in B. "Conflicts" are

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often combined with "replaces".

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</li>

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</ul>

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<ul>

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<li>

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Package A replaces Package B when files installed by B are removed and

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(in some cases) over-written by files in A.

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</li>

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</ul>

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<ul>

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<li>

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Package A provides Package B when all of the files and functionality

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of B are incorporated into A. This mechanism provides a way for users with

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constrained disk space to get only that part of package A which they really

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need.

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</li>

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</ul>

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More detailed information on the use of each these terms can be found in the

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Policy manual.

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<hr>

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<h2><a name="s-pre-depends"></a>7.10 What is meant by Pre-Depends?</h2>

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"Pre-Depends" is a special dependency. In the case of most packages,

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<samp>dpkg</samp> will unpack its archive file (i.e., its <samp>.deb</samp>

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file) independently of whether or not the files on which it depends exist on

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the system. Simplistically, unpacking means that <samp>dpkg</samp> will

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extract the files from the archive file that were meant to be installed on your

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file system, and put them in place. If those packages depend on the

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existence of some other packages on your system, <samp>dpkg</samp> will refuse

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to complete the installation (by executing its "configure" action)

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until the other packages are installed.

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However, for some packages, <samp>dpkg</samp> will refuse even to unpack them

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until certain dependencies are resolved. Such packages are said to

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"Pre-depend" on the presence of some other packages. The Debian

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project provided this mechanism to support the safe upgrading of systems from

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<samp>a.out</samp> format to <samp>ELF</samp> format, where the order

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in which packages were unpacked was critical. There are other large upgrade

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situations where this method is useful, e.g. the packages with the required

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priority and their LibC dependency.

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As before, more detailed information about this can be found in the Policy

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manual.

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<hr>

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<h2><a name="s-pkgstatus"></a>7.11 What is meant by unknown, install, remove, purge and hold in the package status?</h2>

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These "want" flags tell what the user wanted to do with a package (as

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indicated either by the user's actions in the "Select" section of

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<samp>dselect</samp>, or by the user's direct invocations of

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<samp>dpkg</samp>).

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Their meanings are:

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<ul>

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<li>

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unknown - the user has never indicated whether he wants the package

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</li>

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</ul>

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<ul>

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<li>

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install - the user wants the package installed or upgraded

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</li>

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</ul>

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<ul>

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<li>

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remove - the user wants the package removed, but does not want to remove any

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existing configuration files.

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</li>

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</ul>

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<ul>

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<li>

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purge - the user wants the package to be removed completely, including its

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configuration files.

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</li>

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</ul>

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<ul>

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<li>

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hold - the user wants this package not to be processed, i.e., he wants to keep

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the current version with the current status whatever that is.

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</li>

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</ul>

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<hr>

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<h2><a name="s-puttingonhold"></a>7.12 How do I put a package on hold?</h2>

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There are three ways of holding back packages, with dpkg, aptitude or with

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dselect.

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With dpkg, you have to export the list of package selections, with:

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<pre>

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dpkg --get-selections \* > selections.txt

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</pre>

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Then edit the resulting file <code>selections.txt</code>, change the line

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containing the package you wish to hold, e.g. <code>libc6</code>, from this:

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<pre>

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libc6 install

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</pre>

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to this:

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<pre>

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libc6 hold

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</pre>

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Save the file, and reload it into dpkg database with:

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<pre>

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dpkg --set-selections < selections.txt

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</pre>

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With aptitude, you can hold a package using

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<pre>

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aptitude hold package_name

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</pre>

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and remove the hold with

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<pre>

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aptitude unhold package_name

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</pre>

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With dselect, you have to enter the [S]elect screen, find the package you wish

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to hold in its present state, and press the `=' key (or `H'). The changes will

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go live immediately after you exit the [S]elect screen.

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<hr>

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<h2><a name="s-sourcepkgs"></a>7.13 How do I install a source package?</h2>

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Debian source packages can't actually be "installed", they are just

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unpacked in whatever directory you want to build the binary packages they

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produce.

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Source packages are distributed on most of the same mirrors where you can

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obtain the binary packages. If you set up your APT's

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<code>sources.list(5)</code> to include the appropriate "deb-src"

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lines, you'll be able to easily download any source packages by running

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<pre>

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apt-get source foo

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</pre>

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To help you in actually building the source package, Debian source package

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provide the so-called build-dependencies mechanism. This means that the source

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package maintainer keeps a list of other packages that are required to build

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their package. To see how this is useful, run

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<pre>

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apt-get build-dep foo

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</pre>

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before building the source.

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<hr>

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<h2><a name="s-sourcebuild"></a>7.14 How do I build binary packages from a source package?</h2>

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The preferred way to do this is by using various wrapper tools. We'll show how

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it's done using the <samp>devscripts</samp> tools. Install this package if you

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haven't done so already.

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Now, first get the source package:

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<pre>

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apt-get source foo

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</pre>

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and change to the source tree:

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<pre>

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cd foo-*

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</pre>

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Then install needed build-dependencies (if any):

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<pre>

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sudo apt-get build-dep foo

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</pre>

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Then create a dedicated version of your own build (so that you won't get

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confused later when Debian itself releases a new version)

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<pre>

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dch -l local 'Blah blah blah'

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</pre>

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And finally build your package

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<pre>

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debuild -us -uc

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</pre>

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If everything worked out fine, you should now be able to install your package

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by running

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<pre>

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sudo dpkg -i ../*.deb

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</pre>

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If you prefer to do things manually, and don't want to use

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<samp>devscripts</samp>, follow this procedure:

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You will need all of foo_*.dsc, foo_*.tar.gz and foo_*.diff.gz to compile the

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source (note: there is no .diff.gz for some packages that are native to

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Debian).

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Once you have them (<a href="#s-sourcepkgs">How do I install a source package?,

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Section 7.13</a>), if you have the <code>dpkg-dev</code> package installed, the

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following command:

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<pre>

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dpkg-source -x foo_version-revision.dsc

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</pre>

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will extract the package into a directory called <samp>foo-version</samp>.

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If you want just to compile the package, you may cd into

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<samp>foo-version</samp> directory and issue the command

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<pre>

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dpkg-buildpackage -rfakeroot -b

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</pre>

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to build the package (note that this also requires the <code>fakeroot</code>

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package), and then

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<pre>

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dpkg -i ../foo_version-revision_arch.deb

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</pre>

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to install the newly-built package(s).

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<hr>

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<h2><a name="s-creatingdebs"></a>7.15 How do I create Debian packages myself?</h2>

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For a more detailed description on this, read the New Maintainers' Guide,

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available in the <code>maint-guide</code> package, or at <code><a

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href="http://www.debian.org/doc/devel-manuals#maint-guide">http://www.debian.org/doc/devel-manuals#maint-guide</a></code>.

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<hr>

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[ <a href="ch-ftparchives.en.html">previous</a> ]

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[ <a href="index.en.html#contents">Contents</a> ]

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[ <a href="ch-basic_defs.en.html">1</a> ]

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[ <a href="ch-getting.en.html">2</a> ]

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[ <a href="ch-choosing.en.html">3</a> ]

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[ <a href="ch-compat.en.html">4</a> ]

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[ <a href="ch-software.en.html">5</a> ]

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[ <a href="ch-ftparchives.en.html">6</a> ]

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[ 7 ]

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[ <a href="ch-pkgtools.en.html">8</a> ]

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[ <a href="ch-uptodate.en.html">9</a> ]

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[ <a href="ch-kernel.en.html">10</a> ]

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[ <a href="ch-customizing.en.html">11</a> ]

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[ <a href="ch-support.en.html">12</a> ]

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[ <a href="ch-contributing.en.html">13</a> ]

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[ <a href="ch-redistrib.en.html">14</a> ]

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[ <a href="ch-nexttime.en.html">15</a> ]

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[ <a href="ch-faqinfo.en.html">16</a> ]

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[ <a href="ch-pkgtools.en.html">next</a> ]

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<hr>

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The Debian GNU/Linux FAQ

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version 4.0.3, 6 August 2008

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Authors are listed at <a href="ch-faqinfo.en.html#s-authors">Debian FAQ Authors</a>

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</address>

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<hr>

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</body>

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</html>

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