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<h1>
APT User's Guide
<br>Chapter 4 - The Interface
</h1>

<p>
Both that APT <code>dselect</code> method and <code>apt-get</code> 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="footnotes.html#f2" name="fr2">2</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>

<hr>

<h2 id="s4.1">4.1 Startup</h2>

<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 <samp>apt-get
check</samp>.
</p>

<pre>
     # 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
<code>apt-get</code> will refuse to run.
</p>

<pre>
     # apt-get check
     Reading Package Lists... Done
     Building Dependency Tree... Done
     You might want to run apt-get -f 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 (&gt;= 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 (&gt;= 2.01) but 2.0-3 is installed
       cthugha: Depends: svgalibg1 but it is not installed
                Depends: xlib6g (&gt;= 3.3-5) but it is not installed
       libreadlineg2: Conflicts:libreadline2 (&lt;&lt; 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 <code>dpkg</code> missing some subtle relationships between
packages when performing upgrades.  [<a href="footnotes.html#f3"
name="fr3">3</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 <samp>-f</samp> option to <code>apt-get</code> will cause APT to
deduce a possible solution to the problem and then continue on.  The APT
<code>dselect</code> method always supplies the <samp>-f</samp> option to allow
for easy continuation of failed maintainer scripts.
</p>

<p>
However, if the <samp>-f</samp> 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>

<hr>

<h2 id="s4.2">4.2 The Status Report</h2>

<p>
Before proceeding <code>apt-get</code> 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 <samp>-f</samp> option and any
other relevant activities to the command being executed.
</p>

<hr>

<h3 id="s4.2.1">4.2.1 The Extra Package list</h3>

<pre>
     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 <samp>install</samp> command.  The listed packages are often
the result of an Auto Install.
</p>

<hr>

<h3 id="s4.2.2">4.2.2 The Packages to Remove</h3>

<pre>
     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
<samp>-f</samp> 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>

<hr>

<h3 id="s4.2.3">4.2.3 The New Packages list</h3>

<pre>
     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>

<hr>

<h3 id="s4.2.4">4.2.4 The Kept Back list</h3>

<pre>
     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 <samp>apt-get install</samp> or by using <code>dselect</code>
to resolve their problems.
</p>

<hr>

<h3 id="s4.2.5">4.2.5 Held Packages warning</h3>

<pre>
     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>

<hr>

<h3 id="s4.2.6">4.2.6 Final summary</h3>

<p>
Finally, APT will print out a summary of all the changes that will occur.
</p>

<pre>
     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>

<hr>

<h2 id="s4.3">4.3 The Status Display</h2>

<p>
During the download of archives and package files APT prints out a series of
status messages.
</p>

<pre>
     # 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 <em>Get</em> 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
<samp>apt-get update</samp> 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 <em>Forking</em>
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
<em>Connecting</em> to <em>Waiting for file</em> to <em>Downloading</em> or
<em>Resuming</em>.  The final value is the number of bytes downloaded from the
remote site.  Once the download begins this is represented as
<samp>102/10.2k</samp> 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 <samp>-q</samp> option to remove the status display.
</p>

<hr>

<h2 id="s4.4">4.4 Dpkg</h2>

<p>
APT uses <code>dpkg</code> for installing the archives and will switch over to
the <code>dpkg</code> interface once downloading is completed.
<code>dpkg</code> 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>

<hr>

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<p>
APT User's Guide
</p>

<address>
$Id: guide.sgml,v 1.7 2003/04/26 23:26:13 doogie Exp $<br>
<br>
Jason Gunthorpe <code><a href="mailto:jgg@debian.org">mailto:jgg@debian.org</a></code><br>
<br>
</address>
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apt-doc 1.0.1ubuntu2 / usr / share / doc / apt-doc / guide.html / ch4.html
