I started an application with:
mono-service app.exe
Now the problem is that I can’t find it. I tried finding the process, but I can’t find it. When I try to start the application it gives me the following error:
MySql.Data.MySqlClient.MySqlException: There is already an open DataReader associated with this Connection which must be closed first.
You are misinterpreting the error message. It isn’t complaining about another process, it’s complaining about a problem in the program you are trying to execute which happens even if only a single instance is running. You must have a bug that tries to reuse a connection that’s still busy. See also various other questions about the problem, for example this one.