UbuntuHelp:RsyncCdImage

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https://help.ubuntu.com/community/RsyncCdImage

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rsync is a wonderful piece of software that only downloads the parts of a file that have changed. https://launchpad.net/products/rsync is a good resource for more information. A nice thing about the way the Ubuntu CDs are constructed is that it's quite easy to keep an up to date local install CD using rsync. Since the daily CDs generally change quite little, it can be processed quite quickly.

Acquiring the ISO

The various files that you need are at http://cdimage.ubuntu.com It's best to use the torrent file if you can. If you have a local Ubuntu archive mirror or cache, you can also use Jigdo. Rsync is handy for finishing up Jigdo downloads that still have a few missing pieces.

Updating the ISO

A number of the Ubuntu servers also work as rsync servers with quite similar URIs to the websites. For example:

rsync -zhhP rsync://cdimage.ubuntu.com/cdimage/daily-live/current/gutsy-desktop-i386.iso .

will sync the server's daily Gutsy desktop image (for i386) to your local system with an older desktop image already stored on your hard drive. -z is compression, -hh is human readable file size, and -P is a progress indicator. A slightly more advanced script will automate much of the syncing process. To run this script successfully, you will need to set the ISO, DIR, and ISOPATH variables according to your needs.

#!/bin/bash
#Script for updating individual ISO image at cdimage.ubuntu.com (daily/current versions).
#Script written by Henrik Omma

ISO="gutsy-alternate-amd64.iso"
DIR="/media/isos/ubuntu"
ISOPATH="cdimage.ubuntu.com/cdimage/daily/current"

cd $DIR
rsync -Lvv --progress rsync://$ISOPATH/$ISO .
md5sum $ISO | sed -e "s/  / */" > $ISO.md5.local #create identical formatted md5sum file from local copy
wget http://$ISOPATH/MD5SUMS 
grep $ISO MD5SUMS > $ISO.md5.server
rm MD5SUMS

This script does two things. First, it syncs your local ISO image to the most recent ISO image on the Ubuntu servers. It then creates files containing the MD5SUMs of both the local and server images, allowing you to quickly compare the two MD5SUMS and tell if your image was synced correctly.