Creating a Linux (or Minecraft) Macro that would change the seed number to a random number and start the server
Solution 1:
If you are OK with the world being deleted, you can just delete the world folder (using rm). When you restart the server a new world will be generated.
If you do not specify a seed in server.properties, it is only stored in level.dat, meaning that it gets reset when you delete the world folder and chosen randomly the next time you start the server.