OK, unless I set xhost +localhost prior to dialing-up (this solution obtained from here), I cannot start any processes. It appears to be a permissions/ownership problem somewhere. Also, when a user telnets in, this error message appears:-
xhost: unable to open display ""
Now, I have also noticed that when I shutdown, this message:-
stdin: is not a tty
is displayed as the first entry on the shutdown screen (sometimes more than once, i.e. multiple entries), but not in sys logs?
Now, after a bit of poking around, I believe these are related.