<?xml version="1.0" encoding="UTF-8" standalone="no"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Chapter 4. The Interface</title> <meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"/> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/> <link rel="home" href="index.html" title="APT User's Guide"/> <link rel="up" href="index.html" title="APT User's Guide"/> <link rel="prev" href="ch3.html" title="Chapter 3. DSelect"/> </head> <body> <div class="navheader"> <table width="100%" summary="Navigation header"> <tr> <th colspan="3" align="center">Chapter 4. The Interface</th> </tr> <tr> <td align="left"><a accesskey="p" href="ch3.html">Prev</a> </td> <th width="60%" align="center"> </th> <td align="right"> </td> </tr> </table> <hr/> </div> <div class="chapter"> <div class="titlepage"> <div> <div> <h1 class="title"><a id="ch4"/>Chapter 4. The Interface</h1> </div> </div> </div> <div class="toc"> <p> <strong>Table of Contents</strong> </p> <dl class="toc"> <dt> <span class="section"> <a href="ch4.html#s4.1">4.1. Startup</a> </span> </dt> <dt> <span class="section"> <a href="ch4.html#s4.2">4.2. The Status Report</a> </span> </dt> <dt> <span class="section"> <a href="ch4.html#s4.3">4.3. The Status Display</a> </span> </dt> <dt> <span class="section"> <a href="ch4.html#s4.4">4.4. Dpkg</a> </span> </dt> </dl> </div> <p> Both that APT <span class="command"><strong>dselect</strong></span> method and <span class="command"><strong>apt-get</strong></span> share the same interface. It is a simple system that generally tells you what it will do and then goes and does it. <a href="#ftn.idp1242884188" class="footnote" id="idp1242884188"><sup class="footnote">[2]</sup></a> After printing out a summary of what will happen APT then will print out some informative status messages so that you can estimate how far along it is and how much is left to do. </p> <div class="section"> <div class="titlepage"> <div> <div> <h2 class="title"><a id="s4.1"/>4.1. Startup</h2> </div> </div> </div> <p> Before all operations except update, APT performs a number of actions to prepare its internal state. It also does some checks of the system's state. At any time these operations can be performed by running <code class="literal">apt-get check</code>. </p> <pre class="screen"> # apt-get check Reading Package Lists... Done Building Dependency Tree... Done </pre> <p> The first thing it does is read all the package files into memory. APT uses a caching scheme so this operation will be faster the second time it is run. If some of the package files are not found then they will be ignored and a warning will be printed when apt-get exits. </p> <p> The final operation performs a detailed analysis of the system's dependencies. It checks every dependency of every installed or unpacked package and considers if it is OK. Should this find a problem then a report will be printed out and <span class="command"><strong>apt-get</strong></span> will refuse to run. </p> <pre class="screen"> # apt-get check Reading Package Lists... Done Building Dependency Tree... Done You might want to run 'apt --fix-broken install' to correct these. Sorry, but the following packages have unmet dependencies: 9fonts: Depends: xlib6g but it is not installed uucp: Depends: mailx but it is not installed blast: Depends: xlib6g (>= 3.3-5) but it is not installed adduser: Depends: perl-base but it is not installed aumix: Depends: libgpmg1 but it is not installed debiandoc-sgml: Depends: sgml-base but it is not installed bash-builtins: Depends: bash (>= 2.01) but 2.0-3 is installed cthugha: Depends: svgalibg1 but it is not installed Depends: xlib6g (>= 3.3-5) but it is not installed libreadlineg2: Conflicts:libreadline2 (<< 2.1-2.1) </pre> <p> In this example the system has many problems, including a serious problem with libreadlineg2. For each package that has unmet dependencies a line is printed out indicating the package with the problem and the dependencies that are unmet. A short explanation of why the package has a dependency problem is also included. </p> <p> There are two ways a system can get into a broken state like this. The first is caused by <span class="command"><strong>dpkg</strong></span> missing some subtle relationships between packages when performing upgrades. <a href="#ftn.idp1242891684" class="footnote" id="idp1242891684"><sup class="footnote">[3]</sup></a>. The second is if a package installation fails during an operation. In this situation a package may have been unpacked without its dependents being installed. </p> <p> The second situation is much less serious than the first because APT places certain constraints on the order that packages are installed. In both cases supplying the <code class="literal">-f</code> option to <span class="command"><strong>apt-get</strong></span> will cause APT to deduce a possible solution to the problem and then continue on. The APT <span class="command"><strong>dselect</strong></span> method always supplies the <code class="literal">-f</code> option to allow for easy continuation of failed maintainer scripts. </p> <p> However, if the <code class="literal">-f</code> option is used to correct a seriously broken system caused by the first case then it is possible that it will either fail immediately or the installation sequence will fail. In either case it is necessary to manually use dpkg (possibly with forcing options) to correct the situation enough to allow APT to proceed. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h2 class="title"><a id="s4.2"/>4.2. The Status Report</h2> </div> </div> </div> <p> Before proceeding <span class="command"><strong>apt-get</strong></span> will present a report on what will happen. Generally the report reflects the type of operation being performed but there are several common elements. In all cases the lists reflect the final state of things, taking into account the <code class="literal">-f</code> option and any other relevant activities to the command being executed. </p> <div class="section"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="s4.2.1"/>4.2.1. The Extra Package list</h3> </div> </div> </div> <pre class="screen"> The following extra packages will be installed: libdbd-mysql-perl xlib6 zlib1 xzx libreadline2 libdbd-msql-perl mailpgp xdpkg fileutils pinepgp zlib1g xlib6g perl-base bin86 libgdbm1 libgdbmg1 quake-lib gmp2 bcc xbuffy squake pgp-i python-base debmake ldso perl libreadlineg2 ssh </pre> <p> The Extra Package list shows all of the packages that will be installed or upgraded in excess of the ones mentioned on the command line. It is only generated for an <code class="literal">install</code> command. The listed packages are often the result of an Auto Install. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="s4.2.2"/>4.2.2. The Packages to Remove</h3> </div> </div> </div> <pre class="screen"> The following packages will be REMOVED: xlib6-dev xpat2 tk40-dev xkeycaps xbattle xonix xdaliclock tk40 tk41 xforms0.86 ghostview xloadimage xcolorsel xadmin xboard perl-debug tkined xtetris libreadline2-dev perl-suid nas xpilot xfig </pre> <p> The Packages to Remove list shows all of the packages that will be removed from the system. It can be shown for any of the operations and should be given a careful inspection to ensure nothing important is to be taken off. The <code class="literal">-f</code> option is especially good at generating packages to remove so extreme care should be used in that case. The list may contain packages that are going to be removed because they are only partially installed, possibly due to an aborted installation. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="s4.2.3"/>4.2.3. The New Packages list</h3> </div> </div> </div> <pre class="screen"> The following NEW packages will installed: zlib1g xlib6g perl-base libgdbmg1 quake-lib gmp2 pgp-i python-base </pre> <p> The New Packages list is simply a reminder of what will happen. The packages listed are not presently installed in the system but will be when APT is done. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="s4.2.4"/>4.2.4. The Kept Back list</h3> </div> </div> </div> <pre class="screen"> The following packages have been kept back compface man-db tetex-base msql libpaper svgalib1 gs snmp arena lynx xpat2 groff xscreensaver </pre> <p> Whenever the whole system is being upgraded there is the possibility that new versions of packages cannot be installed because they require new things or conflict with already installed things. In this case the package will appear in the Kept Back list. The best way to convince packages listed there to install is with <code class="literal">apt-get install</code> or by using <span class="command"><strong>dselect</strong></span> to resolve their problems. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="s4.2.5"/>4.2.5. Held Packages warning</h3> </div> </div> </div> <pre class="screen"> The following held packages will be changed: cvs </pre> <p> Sometimes you can ask APT to install a package that is on hold, in such a case it prints out a warning that the held package is going to be changed. This should only happen during dist-upgrade or install. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h3 class="title"><a id="s4.2.6"/>4.2.6. Final summary</h3> </div> </div> </div> <p> Finally, APT will print out a summary of all the changes that will occur. </p> <pre class="screen"> 206 packages upgraded, 8 newly installed, 23 to remove and 51 not upgraded. 12 packages not fully installed or removed. Need to get 65.7M/66.7M of archives. After unpacking 26.5M will be used. </pre> <p> The first line of the summary simply is a reduced version of all of the lists and includes the number of upgrades - that is packages already installed that have new versions available. The second line indicates the number of poorly configured packages, possibly the result of an aborted installation. The final line shows the space requirements that the installation needs. The first pair of numbers refer to the size of the archive files. The first number indicates the number of bytes that must be fetched from remote locations and the second indicates the total size of all the archives required. The next number indicates the size difference between the presently installed packages and the newly installed packages. It is roughly equivalent to the space required in /usr after everything is done. If a large number of packages are being removed then the value may indicate the amount of space that will be freed. </p> <p> Some other reports can be generated by using the -u option to show packages to upgrade, they are similar to the previous examples. </p> </div> </div> <div class="section"> <div class="titlepage"> <div> <div> <h2 class="title"><a id="s4.3"/>4.3. The Status Display</h2> </div> </div> </div> <p> During the download of archives and package files APT prints out a series of status messages. </p> <pre class="screen"> # apt-get update Get:1 http://ftp.de.debian.org/debian-non-US/ stable/non-US/ Packages Get:2 http://llug.sep.bnl.gov/debian/ testing/contrib Packages Hit http://llug.sep.bnl.gov/debian/ testing/main Packages Get:4 http://ftp.de.debian.org/debian-non-US/ unstable/binary-i386/ Packages Get:5 http://llug.sep.bnl.gov/debian/ testing/non-free Packages 11% [5 testing/non-free `Waiting for file' 0/32.1k 0%] 2203b/s 1m52s </pre> <p> The lines starting with <span class="emphasis"><em>Get</em></span> are printed out when APT begins to fetch a file while the last line indicates the progress of the download. The first percent value on the progress line indicates the total percent done of all files. Unfortunately since the size of the Package files is unknown <code class="literal">apt-get update</code> estimates the percent done which causes some inaccuracies. </p> <p> The next section of the status line is repeated once for each download thread and indicates the operation being performed and some useful information about what is happening. Sometimes this section will simply read <span class="emphasis"><em>Forking</em></span> which means the OS is loading the download module. The first word after the [ is the fetch number as shown on the history lines. The next word is the short form name of the object being downloaded. For archives it will contain the name of the package that is being fetched. </p> <p> Inside of the single quote is an informative string indicating the progress of the negotiation phase of the download. Typically it progresses from <span class="emphasis"><em>Connecting</em></span> to <span class="emphasis"><em>Waiting for file</em></span> to <span class="emphasis"><em>Downloading</em></span> or <span class="emphasis"><em>Resuming</em></span>. The final value is the number of bytes downloaded from the remote site. Once the download begins this is represented as <code class="literal">102/10.2k</code> indicating that 102 bytes have been fetched and 10.2 kilobytes is expected. The total size is always shown in 4 figure notation to preserve space. After the size display is a percent meter for the file itself. The second last element is the instantaneous average speed. This values is updated every 5 seconds and reflects the rate of data transfer for that period. Finally is shown the estimated transfer time. This is updated regularly and reflects the time to complete everything at the shown transfer rate. </p> <p> The status display updates every half second to provide a constant feedback on the download progress while the Get lines scroll back whenever a new file is started. Since the status display is constantly updated it is unsuitable for logging to a file, use the <code class="literal">-q</code> option to remove the status display. </p> </div> <div class="section"> <div class="titlepage"> <div> <div> <h2 class="title"><a id="s4.4"/>4.4. Dpkg</h2> </div> </div> </div> <p> APT uses <span class="command"><strong>dpkg</strong></span> for installing the archives and will switch over to the <span class="command"><strong>dpkg</strong></span> interface once downloading is completed. <span class="command"><strong>dpkg</strong></span> will also ask a number of questions as it processes the packages and the packages themselves may also ask several questions. Before each question there is usually a description of what it is asking and the questions are too varied to discuss completely here. </p> </div> <div class="footnotes"> <br/> <hr/> <div id="ftn.idp1242884188" class="footnote"> <p><a href="#idp1242884188" class="para"><sup class="para">[2] </sup></a> The <span class="command"><strong>dselect</strong></span> method actually is a set of wrapper scripts to <span class="command"><strong>apt-get</strong></span>. The method actually provides more functionality than is present in <span class="command"><strong>apt-get</strong></span> alone. </p> </div> <div id="ftn.idp1242891684" class="footnote"> <p><a href="#idp1242891684" class="para"><sup class="para">[3] </sup></a> APT however considers all known dependencies and attempts to prevent broken packages </p> </div> </div> </div> <div class="navfooter"> <hr/> <table width="100%" summary="Navigation footer"> <tr> <td align="left"><a accesskey="p" href="ch3.html">Prev</a> </td> <td align="center"> </td> <td align="right"> </td> </tr> <tr> <td align="left" valign="top">Chapter 3. DSelect </td> <td align="center"> <a accesskey="h" href="index.html">Home</a> </td> <td align="right" valign="top"> </td> </tr> </table> </div> </body> </html>