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Introduzione

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/karmic-desktop-i386.iso .

will sync the server's daily Karmic 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 (in KB or MB), and -P is a progress indicator.

Note: If you are using other flavors of Ubuntu don't forget to add the flavor's name in the rsync path after cdimage/, e.g.

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

A slightly more advanced script will automate much of the syncing process. To run this script successfully, you will need to set the DIR variable according to your needs. You can set ISO inside the script or simply pass it in on the command-line (to make it easier to sync multiple ISO images). In some cases you may need to manually set ISOPATH if you're downloading an image not automatically detected. Add "#!/bin/bash" on Top of the script (It is there in editing-mode).

#Script for updating individual ISO image at cdimage.ubuntu.com (daily/current versions).
#Orginal script written by Henrik Omma, slightly adjusted by Bert Verhaeghe, then a bit by Victor Van Hee
#Jeremy Yoder made it try to automatically pick an ISOPATH, adapted to karmic by Christian Bangerter

# Change this next line to the directory where your previously downloaded iso image sits.
DIR="/home/USERNAME/Desktop/karmic"

# Choose only one of the iso files below and uncomment it
ISO="karmic-desktop-amd64.iso"
# ISO="karmic-desktop-i386.iso"
# ISO="karmic-alternate-amd64.iso"
# ISO="karmic-alternate-i386.iso"

# Uncomment the line below if you want a different image not listed below
# ISOPATH="cdimage.ubuntu.com/cdimage/LOCATION/current"

# Default ISO to the first command-line parameter
if [ "$1" != "" ]; then
  ISO=$1
fi

if [ "$ISOPATH" = "" ]; then
  if [[ "$ISO" =~ "-desktop-" ]]; then
    ISOPATH="cdimage.ubuntu.com/cdimage/daily-live/current"
  elif [[ "$ISO" =~ "-alternate-" ]]; then
    ISOPATH="cdimage.ubuntu.com/cdimage/daily/current"
  elif [[ "$ISO" =~ "-dvd-" ]]; then
    ISOPATH="cdimage.ubuntu.com/cdimage/dvd/current"
  elif [[ "$ISO" =~ "-netbook-remix-" ]]; then
    ISOPATH="cdimage.ubuntu.com/cdimage/ubuntu-netbook-remix/daily-live/current"
  elif [[ "$ISO" =~ "-server-" ]]; then
    ISOPATH="cdimage.ubuntu.com/cdimage/ubuntu-server/daily/current"
  else
    echo "Unrecognized distribution, set ISOPATH manually"
    exit 1
  fi
fi

if [ ! -d $DIR ]; then
  echo "Sorry, $DIR does not exist"
  exit
fi

cd $DIR

md5sum $ISO | sed -e "s/  / */" > $ISO.md5.local 
# ^ create identical formatted md5sum file from local copy
echo ""
echo "########################################"
echo "# diff'ing MD5SUMs : local <-> server  #"
echo "########################################"

wget -q http://$ISOPATH/MD5SUMS 
grep $ISO MD5SUMS > $ISO.md5.server
rm MD5SUMS
diff -q $ISO.md5.local $ISO.md5.server

if [ ! $? -eq "0" ]; then
        echo ""
        echo "!!! MD5SUMs differ !!!"
        echo "...Performing rsync..."
        echo "###################"
        echo "# rsync iso image #"
        echo "###################"
        rsync -avzhhP rsync://$ISOPATH/$ISO .
else
        echo ""
        echo "MD5SUMs identical -- no need to Rsync"
        echo ""
        exit 0
fi
echo ""
echo "########################################"
echo "# diff'ing MD5SUMs : local <-> server  #"
echo "########################################"

md5sum $ISO | sed -e "s/  / */" > $ISO.md5.local
diff -q $ISO.md5.local $ISO.md5.server

if [ ! $? -eq "0" ]; then
        echo ""
        echo "!!! MD5SUMs differ !!!"
        echo "!!! Rsync failed!  !!!"
else
        echo ""
        echo "MD5SUMs identical"
        echo "SUCCESS!"
fi
echo ""

This script does three things. First, it creates files containing the MD5SUMs of both the current local and server images, and outputs if the MD5SUMs are identical or not. If they are not identical, it syncs your local ISO image to the most recent ISO image on the Ubuntu servers. It then rechecks the new local MD5SUM and compares it to the server image, and outputs if the MD5SUMs are identical or not.

Using zsync instead

zsync is another implementation of the same algorithm that rsync uses, but does not require special software at the server end. It seems to be more efficient (require less data to be downloaded) for ISO images.

To download or update an image with zsync:

zsync http://cdimage.ubuntu.com/daily-live/current/karmic-desktop-amd64.iso.zsync

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