350 lines
8.0 KiB
HTML
350 lines
8.0 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<HTML
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><HEAD
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><TITLE
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>Why jigdo?</TITLE
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><META
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NAME="GENERATOR"
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CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK
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REL="HOME"
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TITLE="Debian Jigdo mini-HOWTO"
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HREF="index.html"><LINK
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REL="PREVIOUS"
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TITLE="Administrata"
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HREF="administrata.html"><LINK
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REL="NEXT"
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TITLE="How Jigdo Works (optional)"
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HREF="howjigdoworks.html"></HEAD
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><BODY
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CLASS="SECT1"
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BGCOLOR="#FFFFFF"
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TEXT="#000000"
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LINK="#0000FF"
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VLINK="#840084"
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ALINK="#0000FF"
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><DIV
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CLASS="NAVHEADER"
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><TABLE
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SUMMARY="Header navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TH
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COLSPAN="3"
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ALIGN="center"
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>Debian Jigdo mini-HOWTO</TH
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></TR
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><TR
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><TD
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WIDTH="10%"
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ALIGN="left"
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VALIGN="bottom"
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><A
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HREF="administrata.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="80%"
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ALIGN="center"
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VALIGN="bottom"
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></TD
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><TD
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WIDTH="10%"
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ALIGN="right"
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VALIGN="bottom"
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><A
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HREF="howjigdoworks.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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></TABLE
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><HR
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ALIGN="LEFT"
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WIDTH="100%"></DIV
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><DIV
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="WHYJIGDO"
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></A
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>2. Why jigdo?</H1
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN97"
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></A
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>2.1. How Does One Get A Debian ISO Image Set?</H2
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><P
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>If you want a set of Debian CDs there are many ways of getting them. One way is to buy
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them from <A
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HREF="http://www.debian.org/CD/vendors/"
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TARGET="_top"
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>vendors</A
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> who sell Debian CDs.
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This definitely has merit since some of the vendors donate money back to the Debian project.
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Your donations help make sure that Debian is around for a long time.</P
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><P
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>Another way of getting a set of Debian CDs is to burn your own set. This first entails
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obtaining an ISO image and then burning that ISO image to a blank CD. Before jigdo, there
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were two ways of creating Debian CDs:</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Downloading the entire ISO</P
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></LI
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><LI
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><P
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>Using the pseudo-image kit (PIK)</P
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></LI
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></OL
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><P
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>This document is about the newer and better way of obtaining Debian ISO images, using a
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tool called jigdo. In fact, the PIK is now officially dead and all further references to it
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have been removed from this document. The canonical method of getting Debian ISO images is
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with jigdo.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="WHYNOTDOWNLOADTHEWHOLEISOIMAGE"
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></A
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>2.2. Why Not Download The Whole ISO Image?</H2
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><P
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>There are mirrors which offer http and ftp downloads of Debian ISOs. The problem is
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that there are very few mirror sites, and their bandwidth can't support everyone who wants
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Debian ISOs. For example, fsn.hu has reportedly saturated the connection of its provider.
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The outgoing traffic reaches a few terabytes per month!</P
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><P
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>In addition, Debian testing and unstable get updated often. Your ISOs may become
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outdated the same day you download them unless you find some sneaky way of updating them like
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mounting the ISO on a loopback device and using rsync (which is what the PIK did). So if you
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want up-to-date ISO images, you must download a new set of ISO images every day. Clearly,
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this is not the way you want to obtain Debian ISOs!</P
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><P
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>Even if you want to download the stable ISO images, they still get updated every few
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months. Downloading the ISO images will give you up-to-date images for a few months, but
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every time a new revision of Debian stable is released, you'll need to go through the painful
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process of downloading the entire ISO set from scratch. This is not a good use of your time
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and the mirror's resources.</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="WHATISJIGDO"
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></A
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>2.3. What Is Jigdo?</H2
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><P
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>Jigdo (which stands for "Jigsaw Download") was written by <A
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HREF="mailto:atterer@debian.org"
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TARGET="_top"
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>Richard Atterer</A
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> and is released under the GNU GPL.
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It's a tool that allows efficient downloading and updating of an ISO image. Any ISO image.
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Jigdo is not Debian specific, however Debian has chosen it to be the official method of
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downloading ISO images.</P
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><P
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>A common misconception is that jigdo creates ISO images; it doesn't. Let's discuss the
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overall process of how jigdo allows you to obtain an ISO image. Let Adam (a Debian release
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manager) be the person offering the ISO image. Let Betty (a Debian user) be the person who
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wants to download the ISO image.</P
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><P
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></P
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><OL
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TYPE="1"
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><LI
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><P
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>Adam first creates an ISO image suitable for burning a CD. He might use a utility
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like <SPAN
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CLASS="APPLICATION"
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>mkisofs</SPAN
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> or <SPAN
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CLASS="APPLICATION"
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>debian-cd</SPAN
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> to create
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the ISO image. He also creates two small files associated with his newly created image: a
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<TT
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CLASS="FILENAME"
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>.jigdo</TT
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> file and a <TT
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CLASS="FILENAME"
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>.template</TT
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> file. He makes these
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two files available for download to anyone who wants to obtain his ISO image.</P
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></LI
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><LI
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><P
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>Betty then downloads the <TT
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CLASS="FILENAME"
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>.jigdo</TT
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> and
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<TT
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CLASS="FILENAME"
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>.template</TT
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> files. She uses <SPAN
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CLASS="APPLICATION"
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>jigdo-lite</SPAN
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> along
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with these two files to download Adam's ISO image.</P
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></LI
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><LI
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><P
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>When Debian gets updated, Adam creates a new version of the ISO and generates new
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<TT
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CLASS="FILENAME"
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>.jigdo</TT
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> and <TT
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CLASS="FILENAME"
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>.template</TT
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> files.</P
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></LI
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><LI
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><P
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>When Betty wants to update her CDs, she downloads the new <TT
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CLASS="FILENAME"
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>.jigdo</TT
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>
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and <TT
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CLASS="FILENAME"
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>.template</TT
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> files and uses them with
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<SPAN
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CLASS="APPLICATION"
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>jigdo-light</SPAN
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> to update her copy of the ISO images. The important
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thing here is that she only downloads the differences between her old ISO and Adam's new
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ISO. She does not have to re-download the parts that are unchanged.</P
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></LI
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></OL
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><P
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>Jigdo comes with two utilities: <SPAN
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CLASS="APPLICATION"
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>jigdo-file</SPAN
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> (used by Adam)
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which creates the <TT
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CLASS="FILENAME"
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>.jigdo</TT
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> and <TT
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CLASS="FILENAME"
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>.template</TT
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> files, and
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<SPAN
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CLASS="APPLICATION"
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>jigdo-lite</SPAN
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> (used by Betty) which uses these two files to download
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or update the ISO. If all you want to do is obtain/update Debian ISOs, you'll only use
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<SPAN
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CLASS="APPLICATION"
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>jigdo-lite</SPAN
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>. You can forget that jigdo-file even exists. <20>
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:-)</P
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><P
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>Jigdo addresses all the problems with the other methods of obtaining Debian ISO
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images:</P
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><P
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></P
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><UL
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><LI
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><P
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>It's much faster than downloading the entire ISO image.</P
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></LI
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><LI
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><P
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>Unlike downloading the entire ISO image, it can take an outdated CD (or a loop
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mounted outdated ISO image), download <EM
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>only</EM
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> the files that have changed
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since the CD (or ISO image) was created and create a new updated ISO. Very similar to how you
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use cvs to update source code.</P
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></LI
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><LI
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><P
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>jigdo-lite uses wget which, by default, uses http to transfer files. Unlike
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rsync, http is never blocked by firewalls (except the ones behind which you shouldn't be using
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jigdo to begin with).</P
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></LI
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><LI
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><P
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>Jigdo is very kind to the bandwidth of the servers offering the Debian images.
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The Debian mirrors can handle a bigger load of people using jigdo to download Debian images
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than with other methods of getting them.</P
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></LI
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></UL
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><P
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>Clearly, jigdo is the best method of obtaining Debian ISO images.</P
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></DIV
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></DIV
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><DIV
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CLASS="NAVFOOTER"
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><HR
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ALIGN="LEFT"
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WIDTH="100%"><TABLE
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SUMMARY="Footer navigation table"
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WIDTH="100%"
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BORDER="0"
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CELLPADDING="0"
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CELLSPACING="0"
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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><A
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HREF="administrata.html"
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ACCESSKEY="P"
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>Prev</A
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></TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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><A
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HREF="index.html"
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ACCESSKEY="H"
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>Home</A
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></TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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><A
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HREF="howjigdoworks.html"
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ACCESSKEY="N"
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>Next</A
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></TD
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></TR
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><TR
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><TD
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WIDTH="33%"
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ALIGN="left"
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VALIGN="top"
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>Administrata</TD
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><TD
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WIDTH="34%"
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ALIGN="center"
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VALIGN="top"
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> </TD
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><TD
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WIDTH="33%"
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ALIGN="right"
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VALIGN="top"
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>How Jigdo Works (optional)</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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>
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