Springlobby.log
From Spring
springlobby.log (since springlobby 0.248) is the log file of SpringLobby.
On windows it can be found in %LobbyWriteDir%\logs\(year)(month)(day)_(hour)(minute)(second)-springlobby.log, usually %APPDATA%\springlobby\logs\(year)(month)(day)_(hour)(minute)(second)-springlobby.log .
On linux its ~/.springlobby/logs/(year)(month)(day)_(hour)(minute)(second)-springlobby.log .
