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<h1 class="title"><a id="ch1"/>Chapter 1. Introduction</h1>
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<div class="toc">
<p>
<strong>Table of Contents</strong>
</p>
<dl class="toc">
<dt>
<span class="section">
<a href="ch1.html#s1.1">1.1. General</a>
</span>
</dt>
<dt>
<span class="section">
<a href="ch1.html#s1.2">1.2. Terms</a>
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<div>
<div>
<h2 class="title"><a id="s1.1"/>1.1. General</h2>
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<p>
The APT method interface allows APT to acquire archive files (.deb), index
files (Packages, Release, Mirrors) and source files (.tar.gz, .diff). It is a
general, extensible system designed to satisfy all of these requirements:
</p>
<div class="orderedlist">
<ol class="orderedlist">
<li class="listitem">
<p>
Remote methods that download files from a distant site
</p>
</li>
<li class="listitem">
<p>
Resume of aborted downloads
</p>
</li>
<li class="listitem">
<p>
Progress reporting
</p>
</li>
<li class="listitem">
<p>
If-Modified-Since (IMS) checking for index files
</p>
</li>
<li class="listitem">
<p>
In-Line MD5 generation
</p>
</li>
<li class="listitem">
<p>
No-copy in-filesystem methods
</p>
</li>
<li class="listitem">
<p>
Multi-media methods (like CD's)
</p>
</li>
<li class="listitem">
<p>
Dynamic source selection for failure recovery
</p>
</li>
<li class="listitem">
<p>
User interaction for user/password requests and media swaps
</p>
</li>
<li class="listitem">
<p>
Global configuration
</p>
</li>
</ol>
</div>
<p>
Initial releases of APT (0.1.x) used a completely different method interface
that only supported the first 6 items. This new interface deals with the
remainder.
</p>
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<div>
<h2 class="title"><a id="s1.2"/>1.2. Terms</h2>
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<p>
Several terms are used through out the document, they have specific meanings
which may not be immediately evident. To clarify they are summarized here.
</p>
<div class="variablelist">
<dl class="variablelist">
<dt>
<span class="term">source</span>
</dt>
<dd>
<p>
Refers to an item in source list. More specifically it is the broken down
item, that is each source maps to exactly one index file. Archive sources map
to Package files and Source Code sources map to Source files.
</p>
</dd>
<dt>
<span class="term">archive file</span>
</dt>
<dd>
<p>
Refers to a binary package archive (.deb, .rpm, etc).
</p>
</dd>
<dt>
<span class="term">source file</span>
</dt>
<dd>
<p>
Refers to one of the files making up the source code of a package. In debian
it is one of .diff.gz, .dsc. or .tar.gz.
</p>
</dd>
<dt>
<span class="term">URI</span>
</dt>
<dd>
<p>
Universal Resource Identifier (URI) is a super-set of the familiar URL
syntax used by web browsers. It consists of an access specification
followed by a specific location in that access space. The form is
<access>:<location>. Network addresses are given with the form
<access>://[<user>[:<pas>]@]hostname[:port]/<location>.
Some examples:
</p>
<pre class="screen">
file:/var/mirrors/debian/
ftp://ftp.debian.org/debian
ftp://jgg:MooCow@localhost:21/debian
nfs://bigred/var/mirrors/debian
rsync://debian.midco.net/debian
cdrom:Debian 2.0r1 Disk 1/
</pre>
</dd>
<dt>
<span class="term">method</span>
</dt>
<dd>
<p>
There is a one to one mapping of URI access specifiers to methods. A method is
a program that knows how to handle a URI access type and operates according to
the specifications in this file.
</p>
</dd>
<dt>
<span class="term">method instance</span>
</dt>
<dd>
<p>
A specific running method. There can be more than one instance of each method
as APT is capable of concurrent method handling.
</p>
</dd>
<dt>
<span class="term">message</span>
</dt>
<dd>
<p>
A series of lines terminated by a blank line sent down one of the communication
lines. The first line should have the form xxx TAG where xxx are digits
forming the status code and TAG is an informational string
</p>
</dd>
<dt>
<span class="term">acquire</span>
</dt>
<dd>
<p>
The act of bring a URI into the local pathname space. This may simply be
verifying the existence of the URI or actually downloading it from a remote
site.
</p>
</dd>
</dl>
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