Currently there are 2 methods available to sync existing images against a current image, both enable us to only download from a server the difference between what we have locally and what exists on the server cutting down on the required bandwidth.
The first of these is in general already installed and available to use, zsync will need installing.
The following examples assume that you are currently in the same folder that the image to be synced exists in.
From the download page of the tracker copy and paste the command you see, then append the filename of the image you wish to sync.
rsync -tzhhP rsync://cdimage.ubuntu.com/cdimage/xubuntu/daily-live/20150205/vivid-desktop-i386.iso vivid-desktop-i386.iso
In this example the local 32 bit image file is being synced with xubuntu/daily-live/20150205/vivid-desktop-i386.iso.
Once the sync has taken place you will see the result of the sync echoed in the terminal
vivid-desktop-i386.iso 961.00M 100% 9.88MB/s 0:01:37 (xfr#1, to-chk=0/1)
If you run the command in a folder which does not contain an existing image to sync with, you will get no warning and the image will be fully recreated in that folder.
zsync runs from the command you find in the relevant download page on the tracker with no further input
During the sync process, information is echoed to the terminal. First information about the state of the local image against the image found on the server
Read vivid-desktop-amd64.iso. Target 78.6% complete.
Then during download a running total of speed of download and current progress
downloading from http://cdimage.ubuntu.com/xubuntu/daily-live/20150205/vivid-desktop-amd64.iso: #################### 100.0% 4059.4 kBps DONE
Finally, once finished you will be shown whether the checksum matches following verification and how much data was fetched from the server
verifying download...checksum matches OK used 787906560 local, fetched 215340595
If you run the command in a folder which does not contain an existing image to sync with, you will with zsync be warned and can abort the sync with Ctrl+C before too much data is downloaded.
zsync http://cdimage.ubuntu.com/xubuntu/daily-live/20150205/vivid-desktop-amd64.iso.zsync #################### 100.0% 1036.3 kBps DONE No relevent local data found - I will be downloading the whole file. If that's not what you want, CTRL-C out. You should specify the local file is the old version of the file to download with -i (you might have to decompress it with gzip -d first). Or perhaps you just have no data that helps download the file downloading from http://cdimage.ubuntu.com/xubuntu/daily-live/20150205/vivid-desktop-amd64.iso: -------------------- 0.1% 993.6 kBps 16:50 ETA ^C