This directory holds the actual data for the Minecraft servers which are
managed by minecproxy/minecctl.

You need to download the Minecraft server .jar file and place it in this
folder.

The recommended approach is to download the version(s) of your choice
and to store them with version numbers.

So, for example, if you go to the minecraft.net server download page[1]
and download version "1.16.1", then save it in this directory as
"minecraft_server.1.16.1.jar".

Next, create a symlink to the newly downloaded server to make it the default
version by executing "ln -sf minecraft_server.1.16.1.jar server.jar".

Whatever "server.jar" is pointing to will be used as the default server
version.

If you wish to use a particular server version for a particular server
configuration, change the symlink in the corresponding server directory
so that it points to a specific server version.

For example, if server "myworld" should be at version 1.15.1, do the
following (assuming you've already downloaded the corresponding
Minecraft server .jar):

cd myworld
rm server.jar
ln -sf ../minecraft_server.1.15.1.jar server.jar

[1] https://www.minecraft.net/en-us/download/server/