View file File name : ch-maintainerscripts.html Content : <!DOCTYPE html> <html> <head> <meta charset="utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0" /><meta name="generator" content="Docutils 0.17.1: http://docutils.sourceforge.net/" /> <title>6. Package maintainer scripts and installation procedure — Debian Policy Manual v4.6.0.1</title> <link rel="stylesheet" type="text/css" href="_static/pygments.css" /> <link rel="stylesheet" type="text/css" href="_static/nature.css" /> <script data-url_root="./" id="documentation_options" src="_static/documentation_options.js"></script> <script src="_static/jquery.js"></script> <script src="_static/underscore.js"></script> <script src="_static/doctools.js"></script> <link rel="index" title="Index" href="genindex.html" /> <link rel="search" title="Search" href="search.html" /> <link rel="next" title="7. Declaring relationships between packages" href="ch-relationships.html" /> <link rel="prev" title="5. Control files and their fields" href="ch-controlfields.html" /> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="ch-relationships.html" title="7. Declaring relationships between packages" accesskey="N">next</a> |</li> <li class="right" > <a href="ch-controlfields.html" title="5. Control files and their fields" accesskey="P">previous</a> |</li> <li class="nav-item nav-item-0"><a href="index.html">Debian Policy Manual v4.6.0.1</a> »</li> <li class="nav-item nav-item-this"><a href=""><span class="section-number">6. </span>Package maintainer scripts and installation procedure</a></li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="package-maintainer-scripts-and-installation-procedure"> <h1><span class="section-number">6. </span>Package maintainer scripts and installation procedure<a class="headerlink" href="#package-maintainer-scripts-and-installation-procedure" title="Permalink to this headline">¶</a></h1> <section id="introduction-to-package-maintainer-scripts"> <span id="s6-1"></span><h2><span class="section-number">6.1. </span>Introduction to package maintainer scripts<a class="headerlink" href="#introduction-to-package-maintainer-scripts" title="Permalink to this headline">¶</a></h2> <p>It is possible to supply scripts as part of a package which the package management system will run for you when your package is installed, upgraded or removed.</p> <p>These scripts are the control information files <code class="docutils literal notranslate"><span class="pre">preinst</span></code>, <code class="docutils literal notranslate"><span class="pre">postinst</span></code>, <code class="docutils literal notranslate"><span class="pre">prerm</span></code> and <code class="docutils literal notranslate"><span class="pre">postrm</span></code>. They must be proper executable files; if they are scripts (which is recommended), they must start with the usual <code class="docutils literal notranslate"><span class="pre">#!</span></code> convention. They should be readable and executable by anyone, and must not be world-writable.</p> <p>The package management system looks at the exit status from these scripts. It is important that they exit with a non-zero status if there is an error, so that the package management system can stop its processing. For shell scripts this means that you <em>almost always</em> need to use <code class="docutils literal notranslate"><span class="pre">set</span> <span class="pre">-e</span></code> (this is usually true when writing shell scripts, in fact). It is also important, of course, that they exit with a zero status if everything went well.</p> <p>Additionally, packages interacting with users using <code class="docutils literal notranslate"><span class="pre">debconf</span></code> in the <code class="docutils literal notranslate"><span class="pre">postinst</span></code> script should install a <code class="docutils literal notranslate"><span class="pre">config</span></code> script as a control information file. See <a class="reference internal" href="ch-binary.html#s-maintscriptprompt"><span class="std std-ref">Prompting in maintainer scripts</span></a> for details.</p> <p>When a package is upgraded a combination of the scripts from the old and new packages is called during the upgrade procedure. If your scripts are going to be at all complicated you need to be aware of this, and may need to check the arguments to your scripts.</p> <p>Broadly speaking the <code class="docutils literal notranslate"><span class="pre">preinst</span></code> is called before (a particular version of) a package is unpacked, and the <code class="docutils literal notranslate"><span class="pre">postinst</span></code> afterwards; the <code class="docutils literal notranslate"><span class="pre">prerm</span></code> before (a version of) a package is removed and the <code class="docutils literal notranslate"><span class="pre">postrm</span></code> afterwards.</p> <p>Programs called from maintainer scripts should not normally have a path prepended to them. Before installation is started, the package management system checks to see if the programs <code class="docutils literal notranslate"><span class="pre">ldconfig</span></code>, <code class="docutils literal notranslate"><span class="pre">start-stop-daemon</span></code>, and <code class="docutils literal notranslate"><span class="pre">update-rc.d</span></code> can be found via the <code class="docutils literal notranslate"><span class="pre">PATH</span></code> environment variable. Those programs, and any other program that one would expect to be in the <code class="docutils literal notranslate"><span class="pre">PATH</span></code>, should thus be invoked without an absolute pathname. Maintainer scripts should also not reset the <code class="docutils literal notranslate"><span class="pre">PATH</span></code>, though they might choose to modify it by prepending or appending package-specific directories. These considerations really apply to all shell scripts.</p> </section> <section id="maintainer-scripts-idempotency"> <span id="s-idempotency"></span><h2><span class="section-number">6.2. </span>Maintainer scripts idempotency<a class="headerlink" href="#maintainer-scripts-idempotency" title="Permalink to this headline">¶</a></h2> <p>It is necessary for the error recovery procedures that the scripts be idempotent. This means that if it is run successfully, and then it is called again, it doesn’t bomb out or cause any harm, but just ensures that everything is the way it ought to be. If the first call failed, or aborted half way through for some reason, the second call should merely do the things that were left undone the first time, if any, and exit with a success status if everything is OK. <a class="footnote-reference brackets" href="#id8" id="id1">1</a></p> </section> <section id="controlling-terminal-for-maintainer-scripts"> <span id="s-controllingterminal"></span><h2><span class="section-number">6.3. </span>Controlling terminal for maintainer scripts<a class="headerlink" href="#controlling-terminal-for-maintainer-scripts" title="Permalink to this headline">¶</a></h2> <p>Maintainer scripts are not guaranteed to run with a controlling terminal and may not be able to interact with the user. They must be able to fall back to noninteractive behavior if no controlling terminal is available. Maintainer scripts that prompt via a program conforming to the Debian Configuration Management Specification (see <a class="reference internal" href="ch-binary.html#s-maintscriptprompt"><span class="std std-ref">Prompting in maintainer scripts</span></a>) may assume that program will handle falling back to noninteractive behavior.</p> <p>For high-priority prompts without a reasonable default answer, maintainer scripts may abort if there is no controlling terminal. However, this situation should be avoided if at all possible, since it prevents automated or unattended installs. In most cases, users will consider this to be a bug in the package.</p> </section> <section id="exit-status"> <span id="s-exitstatus"></span><h2><span class="section-number">6.4. </span>Exit status<a class="headerlink" href="#exit-status" title="Permalink to this headline">¶</a></h2> <p>Each script must return a zero exit status for success, or a nonzero one for failure, since the package management system looks for the exit status of these scripts and determines what action to take next based on that datum.</p> </section> <section id="summary-of-ways-maintainer-scripts-are-called"> <span id="s-mscriptsinstact"></span><h2><span class="section-number">6.5. </span>Summary of ways maintainer scripts are called<a class="headerlink" href="#summary-of-ways-maintainer-scripts-are-called" title="Permalink to this headline">¶</a></h2> <p>What follows is a summary of all the ways in which maintainer scripts may be called along with what facilities those scripts may rely on being available at that time. Script names preceded by new- are the scripts from the new version of a package being installed, upgraded to, or downgraded to. Script names preceded by old- are the scripts from the old version of a package that is being upgraded from or downgraded from.</p> <p>The <code class="docutils literal notranslate"><span class="pre">preinst</span></code> script may be called in the following ways:</p> <div class="line-block"> <div class="line"><code class="docutils literal notranslate"><span class="pre">new-preinst</span></code> install</div> <div class="line"><code class="docutils literal notranslate"><span class="pre">new-preinst</span></code> install <em>old-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">new-preinst</span></code> upgrade <em>old-version</em></div> </div> <blockquote> <div><p>The package will not yet be unpacked, so the <code class="docutils literal notranslate"><span class="pre">preinst</span></code> script cannot rely on any files included in its package. Only essential packages and pre-dependencies (<code class="docutils literal notranslate"><span class="pre">Pre-Depends</span></code>) may be assumed to be available. Pre-dependencies will have been configured at least once, but at the time the <code class="docutils literal notranslate"><span class="pre">preinst</span></code> is called they may only be in an “Unpacked” or “Half-Configured” state if a previous version of the pre-dependency was completely configured and has not been removed since then.</p> </div></blockquote> <dl class="simple"> <dt><code class="docutils literal notranslate"><span class="pre">old-preinst</span></code> abort-upgrade <em>new-version</em></dt><dd><p>Called during error handling of an upgrade that failed after unpacking the new package because the <code class="docutils literal notranslate"><span class="pre">postrm</span> <span class="pre">upgrade</span></code> action failed. The unpacked files may be partly from the new version or partly missing, so the script cannot rely on files included in the package. Package dependencies may not be available. Pre-dependencies will be at least “Unpacked” following the same rules as above, except they may be only “Half-Installed” if an upgrade of the pre-dependency failed. <a class="footnote-reference brackets" href="#id9" id="id2">2</a></p> </dd> </dl> <p>The <code class="docutils literal notranslate"><span class="pre">postinst</span></code> script may be called in the following ways:</p> <dl class="simple"> <dt><code class="docutils literal notranslate"><span class="pre">postinst</span></code> configure <em>most-recently-configured-version</em></dt><dd><p>The files contained in the package will be unpacked. All package dependencies will at least be “Unpacked”. If there are no circular dependencies involved, all package dependencies will be configured. For behavior in the case of circular dependencies, see the discussion in <a class="reference internal" href="ch-relationships.html#s-binarydeps"><span class="std std-ref">Binary Dependencies - Depends, Recommends, Suggests, Enhances, Pre-Depends</span></a>.</p> </dd> </dl> <div class="line-block"> <div class="line"><code class="docutils literal notranslate"><span class="pre">old-postinst</span></code> abort-upgrade <em>new-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">conflictor's-postinst</span></code> abort-remove in-favour <em>package</em> <em>new-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">postinst</span></code> abort-remove</div> <div class="line"><code class="docutils literal notranslate"><span class="pre">deconfigured's-postinst</span></code> abort-deconfigure in-favour <em>failed-install-package</em> <em>version</em> [ removing conflicting-package version ]</div> </div> <blockquote> <div><p>The files contained in the package will be unpacked. All package dependencies will at least be “Half-Installed” and will have previously been configured and not removed. However, dependencies may not be configured or even fully unpacked in some error situations. <a class="footnote-reference brackets" href="#id10" id="id3">3</a> The <code class="docutils literal notranslate"><span class="pre">postinst</span></code> should still attempt any actions for which its dependencies are required, since they will normally be available, but consider the correct error handling approach if those actions fail. Aborting the <code class="docutils literal notranslate"><span class="pre">postinst</span></code> action if commands or facilities from the package dependencies are not available is often the best approach.</p> </div></blockquote> <p>The <code class="docutils literal notranslate"><span class="pre">prerm</span></code> script may be called in the following ways:</p> <div class="line-block"> <div class="line"><code class="docutils literal notranslate"><span class="pre">prerm</span></code> remove</div> <div class="line"><code class="docutils literal notranslate"><span class="pre">old-prerm</span></code> upgrade <em>new-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">conflictor's-prerm</span></code> remove in-favour package <em>new-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">deconfigured's-prerm</span></code> deconfigure in-favour <em>package-being-installed</em> <em>version</em> [removing conflicting-package version]</div> </div> <blockquote> <div><p>The package whose <code class="docutils literal notranslate"><span class="pre">prerm</span></code> is being called will be at least “Half-Installed”. All package dependencies will at least be “Half-Installed” and will have previously been configured and not removed. If there was no error, all dependencies will at least be “Unpacked”, but these actions may be called in various error states where dependencies are only “Half-Installed” due to a partial upgrade.</p> </div></blockquote> <dl class="simple"> <dt><code class="docutils literal notranslate"><span class="pre">new-prerm</span></code> failed-upgrade <em>old-version</em></dt><dd><p>Called during error handling when <code class="docutils literal notranslate"><span class="pre">prerm</span> <span class="pre">upgrade</span></code> fails. The new package will not yet be unpacked, and all the same constraints as for <code class="docutils literal notranslate"><span class="pre">preinst</span> <span class="pre">upgrade</span></code> apply.</p> </dd> </dl> <p>The <code class="docutils literal notranslate"><span class="pre">postrm</span></code> script may be called in the following ways:</p> <div class="line-block"> <div class="line"><code class="docutils literal notranslate"><span class="pre">postrm</span></code> remove</div> <div class="line"><code class="docutils literal notranslate"><span class="pre">postrm</span></code> purge</div> <div class="line"><code class="docutils literal notranslate"><span class="pre">old-postrm</span></code> upgrade <em>new-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">disappearer's-postrm</span></code> disappear overwriter <em>overwriter-version</em></div> </div> <blockquote> <div><p>The <code class="docutils literal notranslate"><span class="pre">postrm</span></code> script is called after the package’s files have been removed or replaced. The package whose <code class="docutils literal notranslate"><span class="pre">postrm</span></code> is being called may have previously been deconfigured and only be “Unpacked”, at which point subsequent package changes do not consider its dependencies. Therefore, all <code class="docutils literal notranslate"><span class="pre">postrm</span></code> actions must only rely on essential packages and must gracefully skip any actions that require the package’s dependencies if those dependencies are unavailable. <a class="footnote-reference brackets" href="#id11" id="id4">4</a></p> </div></blockquote> <dl class="simple"> <dt><code class="docutils literal notranslate"><span class="pre">new-postrm</span></code> failed-upgrade <em>old-version</em></dt><dd><p>Called when the old <code class="docutils literal notranslate"><span class="pre">postrm</span> <span class="pre">upgrade</span></code> action fails. The new package will be unpacked, but only essential packages and pre-dependencies can be relied on. Pre-dependencies will either be configured or will be “Unpacked” or “Half-Configured” but previously had been configured and was never removed.</p> </dd> </dl> <div class="line-block"> <div class="line"><code class="docutils literal notranslate"><span class="pre">new-postrm</span></code> abort-install</div> <div class="line"><code class="docutils literal notranslate"><span class="pre">new-postrm</span></code> abort-install <em>old-version</em></div> <div class="line"><code class="docutils literal notranslate"><span class="pre">new-postrm</span></code> abort-upgrade <em>old-version</em></div> </div> <blockquote> <div><p>Called before unpacking the new package as part of the error handling of <code class="docutils literal notranslate"><span class="pre">preinst</span></code> failures. May assume the same state as <code class="docutils literal notranslate"><span class="pre">preinst</span></code> can assume.</p> </div></blockquote> </section> <section id="details-of-unpack-phase-of-installation-or-upgrade"> <span id="s-unpackphase"></span><h2><span class="section-number">6.6. </span>Details of unpack phase of installation or upgrade<a class="headerlink" href="#details-of-unpack-phase-of-installation-or-upgrade" title="Permalink to this headline">¶</a></h2> <p>The procedure on installation/upgrade/overwrite/disappear (i.e., when running <code class="docutils literal notranslate"><span class="pre">dpkg</span> <span class="pre">--unpack</span></code>, or the unpack stage of <code class="docutils literal notranslate"><span class="pre">dpkg</span> <span class="pre">--install</span></code>) is as follows. <a class="footnote-reference brackets" href="#id12" id="id5">5</a> In each case, if a major error occurs (unless listed below) the actions are, in general, run backwards - this means that the maintainer scripts are run with different arguments in reverse order. These are the “error unwind” calls listed below.</p> <ol class="arabic"> <li><p>Notify the currently installed package:</p> <ol class="loweralpha"> <li><p>If a version of the package is already “Installed”, call</p> <pre class="literal-block">old-prerm upgrade <em>new-version</em></pre> </li> <li><p>If the script runs but exits with a non-zero exit status, <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> will attempt:</p> <pre class="literal-block">new-prerm failed-upgrade <em>old-version</em></pre> <p>If this works, the upgrade continues. If this does not work, the error unwind:</p> <pre class="literal-block"><em>old-postinst</em> abort-upgrade <em>new-version</em></pre> <p>If this works, then the <em>old-version</em> is “Installed”, if not, the old version is in a “Half-Configured” state.</p> </li> </ol> </li> <li><p>If a “conflicting” package is being removed at the same time, or if any package will be broken (due to <code class="docutils literal notranslate"><span class="pre">Breaks</span></code>):</p> <ol class="loweralpha"> <li><p>If <code class="docutils literal notranslate"><span class="pre">--auto-deconfigure</span></code> is specified, call, for each package to be deconfigured due to <code class="docutils literal notranslate"><span class="pre">Breaks</span></code>:</p> <pre class="literal-block"><em>deconfigured's-prerm</em> deconfigure \ in-favour <em>package-being-installed</em> <em>version</em></pre> <p>Error unwind:</p> <pre class="literal-block"><em>deconfigured's-postinst</em> abort-deconfigure \ in-favour <em>package-being-installed-but-failed</em> <em>version</em></pre> <p>The deconfigured packages are marked as requiring configuration, so that if <code class="docutils literal notranslate"><span class="pre">--install</span></code> is used they will be configured again if possible.</p> </li> <li><p>If any packages depended on a conflicting package being removed and <code class="docutils literal notranslate"><span class="pre">--auto-deconfigure</span></code> is specified, call, for each such package:</p> <pre class="literal-block"><em>deconfigured's-prerm</em> deconfigure \ in-favour <em>package-being-installed</em> <em>version</em> \ removing <em>conflicting-package</em> <em>version</em></pre> <p>Error unwind:</p> <pre class="literal-block"><em>deconfigured's-postinst</em> abort-deconfigure \ in-favour <em>package-being-installed-but-failed</em> <em>version</em> \ removing <em>conflicting-package</em> <em>version</em></pre> <p>The deconfigured packages are marked as requiring configuration, so that if <code class="docutils literal notranslate"><span class="pre">--install</span></code> is used they will be configured again if possible.</p> </li> <li><p>To prepare for removal of each conflicting package, call:</p> <pre class="literal-block"><em>conflictor's-prerm</em> remove \ in-favour <em>package</em> <em>new-version</em></pre> <p>Error unwind:</p> <pre class="literal-block"><em>conflictor's-postinst</em> abort-remove \ in-favour <em>package</em> <em>new-version</em></pre> </li> </ol> </li> <li><p>Run the <code class="docutils literal notranslate"><span class="pre">preinst</span></code> of the new package:</p> <ol class="loweralpha"> <li><p>If the package is being upgraded, call:</p> <pre class="literal-block"><em>new-preinst</em> upgrade <em>old-version</em></pre> <p>If this fails, we call:</p> <pre class="literal-block"><em>new-postrm</em> abort-upgrade <em>old-version</em></pre> <ol class="lowerroman"> <li><p>If that works, then</p> <pre class="literal-block"><em>old-postinst</em> abort-upgrade <em>new-version</em></pre> <p>is called. If this works, then the old version is in an “Installed” state, or else it is left in an “Unpacked” state.</p> </li> <li><p>If it fails, then the old version is left in an “Half-Installed” state.</p></li> </ol> </li> <li><p>Otherwise, if the package had some configuration files from a previous version installed (i.e., it is in the “Config-Files” state):</p> <pre class="literal-block"><em>new-preinst</em> install <em>old-version</em></pre> <p>Error unwind:</p> <pre class="literal-block"><em>new-postrm</em> abort-install <em>old-version</em></pre> <p>If this fails, the package is left in a “Half-Installed” state, which requires a reinstall. If it works, the packages is left in a “Config-Files” state.</p> </li> <li><p>Otherwise (i.e., the package was completely purged):</p> <pre class="literal-block"><em>new-preinst</em> install</pre> <p>Error unwind:</p> <pre class="literal-block"><em>new-postrm</em> abort-install</pre> <p>If the error-unwind fails, the package is in a “Half-Installed” phase, and requires a reinstall. If the error unwind works, the package is in the “Not-Installed” state.</p> </li> </ol> </li> <li><p>The new package’s files are unpacked, overwriting any that may be on the system already, for example any from the old version of the same package or from another package. Backups of the old files are kept temporarily, and if anything goes wrong the package management system will attempt to put them back as part of the error unwind.</p> <p>It is an error for a package to contain files which are on the system in another package, unless <code class="docutils literal notranslate"><span class="pre">Replaces</span></code> is used (see <a class="reference internal" href="ch-relationships.html#s-replaces"><span class="std std-ref">Overwriting files and replacing packages - Replaces</span></a>).</p> <p>It is a more serious error for a package to contain a plain file or other kind of non-directory where another package has a directory (again, unless <code class="docutils literal notranslate"><span class="pre">Replaces</span></code> is used). This error can be overridden if desired using <code class="docutils literal notranslate"><span class="pre">--force-overwrite-dir</span></code>, but this is not advisable.</p> <p>Packages which overwrite each other’s files produce behavior which, though deterministic, is hard for the system administrator to understand. It can easily lead to “missing” programs if, for example, a package is unpacked which overwrites a file from another package, and is then removed again. <a class="footnote-reference brackets" href="#id13" id="id6">6</a></p> <p>A directory will never be replaced by a symbolic link to a directory or vice versa; instead, the existing state (symlink or not) will be left alone and <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> will follow the symlink if there is one.</p> </li> <li><p>If the package is being upgraded:</p> <ol class="loweralpha"> <li><p>Call:</p> <pre class="literal-block"><em>old-postrm</em> upgrade <em>new-version</em></pre> </li> <li><p>If this fails, <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> will attempt:</p> <pre class="literal-block"><em>new-postrm</em> failed-upgrade <em>old-version</em></pre> <p>If this works, installation continues. If not, Error unwind:</p> <pre class="literal-block"><em>old-preinst</em> abort-upgrade <em>new-version</em></pre> <p>If this fails, the old version is left in a “Half-Installed” state. If it works, dpkg now calls:</p> <pre class="literal-block"><em>new-postrm</em> abort-upgrade <em>old-version</em></pre> <p>If this fails, the old version is left in a “Half-Installed” state. If it works, dpkg now calls:</p> <pre class="literal-block"><em>old-postinst</em> abort-upgrade <em>new-version</em></pre> <p>If this fails, the old version is in an “Unpacked” state.</p> </li> </ol> <p>This is the point of no return. If <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> gets this far, it won’t back off past this point if an error occurs. This will leave the package in a fairly bad state, which will require a successful re-installation to clear up, but it’s when <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> starts doing things that are irreversible.</p> </li> <li><p>Any files which were in the old version of the package but not in the new are removed.</p></li> <li><p>The new file list replaces the old.</p></li> <li><p>The new maintainer scripts replace the old.</p></li> <li><p>Any packages all of whose files have been overwritten during the installation, and which aren’t required for dependencies, are considered to have been removed. For each such package</p> <ol class="loweralpha"> <li><p><code class="docutils literal notranslate"><span class="pre">dpkg</span></code> calls:</p> <pre class="literal-block"><em>disappearer's-postrm</em> disappear \ <em>overwriter</em> <em>overwriter-version</em></pre> </li> <li><p>The package’s maintainer scripts are removed.</p></li> <li><p>It is noted in the status database as being in a sane state, namely “Not-Installed” (any conffiles it may have are ignored, rather than being removed by <code class="docutils literal notranslate"><span class="pre">dpkg</span></code>). Note that disappearing packages do not have their prerm called, because <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> doesn’t know in advance that the package is going to vanish.</p></li> </ol> </li> <li><p>Any files in the package we’re unpacking that are also listed in the file lists of other packages are removed from those lists. (This will lobotomize the file list of the “conflicting” package if there is one.)</p></li> <li><p>The backup files made during installation, above, are deleted.</p></li> <li><p>The new package’s status is now sane, and recorded as “Unpacked”.</p> <p>Here is another point of no return: if the conflicting package’s removal fails we do not unwind the rest of the installation. The conflicting package is left in a half-removed limbo.</p> </li> <li><p>If there was a conflicting package we go and do the removal actions (described below), starting with the removal of the conflicting package’s files (any that are also in the package being unpacked have already been removed from the conflicting package’s file list, and so do not get removed now).</p></li> </ol> </section> <section id="details-of-configuration"> <span id="s-configdetails"></span><h2><span class="section-number">6.7. </span>Details of configuration<a class="headerlink" href="#details-of-configuration" title="Permalink to this headline">¶</a></h2> <p>When we configure a package (this happens with <code class="docutils literal notranslate"><span class="pre">dpkg</span> <span class="pre">--install</span></code> and <code class="docutils literal notranslate"><span class="pre">dpkg</span> <span class="pre">--configure</span></code>), we first update any <code class="docutils literal notranslate"><span class="pre">conffile</span></code>s and then call:</p> <pre class="literal-block"><em>postinst</em> configure <em>most-recently-configured-version</em></pre> <p>No attempt is made to unwind after errors during configuration. If the configuration fails, the package is in a “Half-Configured” state, and an error message is generated.</p> <p>If there is no most recently configured version <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> will pass a null argument. <a class="footnote-reference brackets" href="#id14" id="id7">7</a></p> </section> <section id="details-of-removal-and-or-configuration-purging"> <span id="s-removedetails"></span><h2><span class="section-number">6.8. </span>Details of removal and/or configuration purging<a class="headerlink" href="#details-of-removal-and-or-configuration-purging" title="Permalink to this headline">¶</a></h2> <ol class="arabic"> <li><pre class="literal-block"><em>prerm</em> remove</pre> <p>If prerm fails during replacement due to conflict</p> <pre class="literal-block"><em>conflictor's-postinst</em> abort-remove \ in-favour <em>package</em> <em>new-version</em></pre> <p>Or else we call:</p> <pre class="literal-block"><em>postinst</em> abort-remove</pre> <p>If this fails, the package is in a “Half-Configured” state, or else it remains “Installed”.</p> </li> <li><p>The package’s files are removed (except <code class="docutils literal notranslate"><span class="pre">conffile</span></code>s).</p></li> <li><pre class="literal-block"><em>postrm</em> remove</pre> <p>If it fails, there’s no error unwind, and the package is in an “Half-Installed” state.</p> </li> <li><p>All the maintainer scripts except the <code class="docutils literal notranslate"><span class="pre">postrm</span></code> are removed.</p> <p>If we aren’t purging the package we stop here. Note that packages which have no <code class="docutils literal notranslate"><span class="pre">postrm</span></code> and no <code class="docutils literal notranslate"><span class="pre">conffile</span></code>s are automatically purged when removed, as there is no difference except for the <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> status.</p> </li> <li><p>The <code class="docutils literal notranslate"><span class="pre">conffile</span></code>s and any backup files (<code class="docutils literal notranslate"><span class="pre">~</span></code>-files, <code class="docutils literal notranslate"><span class="pre">#*#</span></code> files, <code class="docutils literal notranslate"><span class="pre">%</span></code>-files, <code class="docutils literal notranslate"><span class="pre">.dpkg-{old,new,tmp}</span></code>, etc.) are removed.</p></li> <li><pre class="literal-block"><em>postrm</em> purge</pre> <p>If this fails, the package remains in a “Config-Files” state.</p> </li> <li><p>The package’s file list is removed.</p></li> </ol> <dl class="footnote brackets"> <dt class="label" id="id8"><span class="brackets"><a class="fn-backref" href="#id1">1</a></span></dt> <dd><p>This is so that if an error occurs, the user interrupts <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> or some other unforeseen circumstance happens you don’t leave the user with a badly-broken package when <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> attempts to repeat the action.</p> </dd> <dt class="label" id="id9"><span class="brackets"><a class="fn-backref" href="#id2">2</a></span></dt> <dd><p>This can happen if the new version of the package no longer pre-depends on a package that had been partially upgraded.</p> </dd> <dt class="label" id="id10"><span class="brackets"><a class="fn-backref" href="#id3">3</a></span></dt> <dd><p>For example, suppose packages foo and bar are “Installed” with foo depending on bar. If an upgrade of bar were started and then aborted, and then an attempt to remove foo failed because its <code class="docutils literal notranslate"><span class="pre">prerm</span></code> script failed, foo’s <code class="docutils literal notranslate"><span class="pre">postinst</span> <span class="pre">abort-remove</span></code> would be called with bar only “Half-Installed”.</p> </dd> <dt class="label" id="id11"><span class="brackets"><a class="fn-backref" href="#id4">4</a></span></dt> <dd><p>This is often done by checking whether the command or facility the <code class="docutils literal notranslate"><span class="pre">postrm</span></code> intends to call is available before calling it. For example:</p> <div class="highlight-default notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">[</span> <span class="s2">"$1"</span> <span class="o">=</span> <span class="n">purge</span> <span class="p">]</span> <span class="o">&&</span> <span class="p">[</span> <span class="o">-</span><span class="n">e</span> <span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">share</span><span class="o">/</span><span class="n">debconf</span><span class="o">/</span><span class="n">confmodule</span> <span class="p">];</span> <span class="n">then</span> <span class="o">.</span> <span class="o">/</span><span class="n">usr</span><span class="o">/</span><span class="n">share</span><span class="o">/</span><span class="n">debconf</span><span class="o">/</span><span class="n">confmodule</span> <span class="n">db_purge</span> <span class="n">fi</span> </pre></div> </div> <p>in <code class="docutils literal notranslate"><span class="pre">postrm</span></code> purges the <code class="docutils literal notranslate"><span class="pre">debconf</span></code> configuration for the package if debconf is installed.</p> </dd> <dt class="label" id="id12"><span class="brackets"><a class="fn-backref" href="#id5">5</a></span></dt> <dd><p>See <a class="reference internal" href="ap-flowcharts.html"><span class="doc">Maintainer script flowcharts</span></a> for flowcharts illustrating the processes described here.</p> </dd> <dt class="label" id="id13"><span class="brackets"><a class="fn-backref" href="#id6">6</a></span></dt> <dd><p>Part of the problem is due to what is arguably a bug in <code class="docutils literal notranslate"><span class="pre">dpkg</span></code>.</p> </dd> <dt class="label" id="id14"><span class="brackets"><a class="fn-backref" href="#id7">7</a></span></dt> <dd><p>Historical note: Truly ancient (pre-1997) versions of <code class="docutils literal notranslate"><span class="pre">dpkg</span></code> passed <code class="docutils literal notranslate"><span class="pre"><unknown></span></code> (including the angle brackets) in this case. Even older ones did not pass a second argument at all, under any circumstance. Note that upgrades using such an old dpkg version are unlikely to work for other reasons, even if this old argument behavior is handled by your postinst script.</p> </dd> </dl> </section> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="index.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#">6. Package maintainer scripts and installation procedure</a><ul> <li><a class="reference internal" href="#introduction-to-package-maintainer-scripts">6.1. Introduction to package maintainer scripts</a></li> <li><a class="reference internal" href="#maintainer-scripts-idempotency">6.2. Maintainer scripts idempotency</a></li> <li><a class="reference internal" href="#controlling-terminal-for-maintainer-scripts">6.3. Controlling terminal for maintainer scripts</a></li> <li><a class="reference internal" href="#exit-status">6.4. Exit status</a></li> <li><a class="reference internal" href="#summary-of-ways-maintainer-scripts-are-called">6.5. Summary of ways maintainer scripts are called</a></li> <li><a class="reference internal" href="#details-of-unpack-phase-of-installation-or-upgrade">6.6. Details of unpack phase of installation or upgrade</a></li> <li><a class="reference internal" href="#details-of-configuration">6.7. Details of configuration</a></li> <li><a class="reference internal" href="#details-of-removal-and-or-configuration-purging">6.8. 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