1. Go to www.java.com and install the latest Java Runtime Environment, see also requirements, if a suitable JRE does not exist already on the computer.
2. Download and unzip the file called jacksum-1.7.0.zip.
cd Downloadverzeichnis
unzip jacksum-1.7.0.zip
3. Start Jacksum in a terminal by typing
cd Installationfolder
java -jar jacksum.jar
4. In order to start Jacksum with more comfort from any directory
jacksum
you have to modify the launch script that is part of the distribution and place it in a folder that is reachable within your PATH environment variable. Also make sure that the user has execute permissions on the file (man chmod). Alternatively you can set also an alias (e. g. alias jacksum="java -jar "<path to jacksum.jar>"/jacksum.jar)