It's pretty simple just download the zip archive from here.
Unzip and edit the sh script sunflow.sh
from the sunflow folder.
By default the script is:
#/bin/sh
mem=1G
java -Xmx$mem -server -jar sunflow.jar $*
If we run this script will have this error :
$ sh sunflow.sh
Invalid maximum heap size: -Xmx1G
Could not create the Java virtual machine.
The solution is:
$ whereis java
java: /usr/bin/java ...
Now change the script :
#!/bin/bash
/usr/bin/java -Xmx1024M -server -jar sunflow.jar $*
And run it ...
$ sh sunflow.sh
The result is :