Unix VoxelMap waypoints disappear constantly on LAN

[Kahless61]

I play FTB Ultimate over LAN, one computer Hosts, the other computer Joins. The Joining computer loses waypoints every time it joins. The Serving computer keeps its waypoints.
Both computers run Ubuntu. The problem is exactly as described when I switch which computer hosts and which one joins (always the joining computer loses its waypoints).

One thing to note, usually both computers start and stop playing at about the same time, so I'm not sure if the waypoints are lost if, say, the joining computer disconnects and reconnects while the host stays up. I could test later this evening (EST).

I'd greatly appreciate any help in not only finding out how to fix this, but also if I could recover some of my waypoints.

 

[gattsuru]

Open To Lan setups randomly select an ephemeral port every time the world is reopened to lan, while most minimaps save waypoint based on IP address or computer name then port number. Rei's Minimap has a similar issue, since the use of port as part of the naming schema is actually a bit of Minecraft's internal code, and the problem is independent of operating system. You'll also run into a related issue over the longer-term, if the server computer is set to use DHCP -- as soon as the server computer's IP address changes (which can take weeks, or happen on reset or overnight), it'll select a new file for you waypoint data.

There are a couple workarounds. The old waypoint file does still exist, and it can be moved to the new server name. That's rather tedious, though. Some mods exist that let you determine which port the LAN server uses, or force it to a single port instead of a random selection -- but there are potential issues with reliability, so I can't recommend any.

The most complete solution is to set your serving machine to a static IP address (or have your router/DHCP set to give the serving machine the same IP address always), run the full server configuration on your server machine, and have both computers join to that server through that IP address.

 

[Kahless61]

Wow, thanks for the detailed answer. I did notice it with REI as well back when I played on Direwolf20 pack (before Ultimate). It's nice to see that there's a good understanding of the problem.
Thanks again.