I have to admit that I wasn't being brilliant and didn't figure this out myself. I had set up a Raspberry Pi with fidigi/grig and Raspbian to control an 817 according to directions I found. I was trying to figure out an answer to your question in a way that you would understand. I looked around for something which would explain the process and found the note I posted. In Unix/Linux, many problems can be traced to permission settings. As Unix has its roots in big computers that many people use at the same time, permission to use parts of it are only allowed to certain people. There are programs the administrators get to use and there are programs everybody gets to use. I have used Unix for a long time but I wouldn't say that I am an expert. As with many of us, I kind of lean on the shoulders of others and contribute what I can.
Glad you got it working.
Jeff, K7AIL CN87