Download Changes

Brandon Rozek

April 12, 2020

When testing daily ISO images, it is useful to only download the parts of the ISO that has changed since the previous days. That way we can preserve time and bandwidth.

Rsync method

This approach requires server-side support, and a lot of flags specified.

rsync --times \
  --compress --partial \
  --progress --stats \
  --human-readable \
  --human-readable \
  rsync://cdimage.ubuntu.com/cdimage/kubuntu/daily-live/20200412/focal-desktop-amd64.iso \
  kubuntu-focal-desktop-amd64.iso
Flag Description
--times Transfer modification times along with the files.
--compress Compress the file data during transit.
--partial Keep partial downloads if interrupted.
--progress Print information showing the progress of the /transfer.
--stats Print a set of statistics on the file transfer.
--human-readable Output numbers in a more human readable format, can use up to 3 times.

Zsync method

This approach does not involve adding a bunch of flags, but it does require the provider to have a .zsync file on their server and for the user to have the zync package installed. This package typically isn’t installed by default on most systems.

zsync http://cdimage.ubuntu.com/kubuntu/daily-live/20200412/focal-desktop-amd64.iso.zsync