Overviewer was used to render the minecraft map, but has since been abandoned in favor of dynmap
Usually the render is created from a backup that is downloaded from the vps.
The arguments to run overviewer are:
overviewer.exe --rendermodes=smooth-lighting [PATH_TO_SERVER_FILES] [PATH_TO_RENDER]
To use overviewer with less cores use the argument -p <number_of_cores>
Unrar: unrar x /source.rar /destination
NO -X just x
For information see these pages: