Up to this point I’ve been using a hardcoded
Option "Rotate" "CCW"
in my /etc/X11/xorg.conf file to get a portrait-mode display on my right-hand monitor, as described in grisly detail there.
That kills xrandr, which prevented any further display configuration and seemed to sometimes kill off the screensaver. Maybe the screens would blank and then power down, maybe they’d just power down, maybe they’d be on all the time.
However, simply eliminating the hardcoded Rotate didn’t solve the problem, as xrandr refused to do anything. The appropriate command-line syntax isn’t obvious to the casual observer, but this was alleged to work: xrandr -o left.
Come to find out, after considerable digging, that one must add this secret incantation to each Display stanza in /etc/X11/xorg.conf:
Option "RandRRotation" "on"
And, perforce, remove the Rotate option.
That’s evidently due to the fact I’m using the proprietary nVidia driver, which I think everybody does.
Log out, Ctrl-Alt-Backspace to restart the X server, log back in again, and shazam the cute little Display applet in the Settings Manager actually works. Not only that, but you can specify Left rotation for Display 1 and that actually works, too.
Update: but, alas, it seems to not be sticky between sessions. Worse, there seems to be no combination of xrandr parameters that can rotate the right-hand screen from a console on the other or, presumably, from a startup script. It is not obvious what this means, either:
This option selects the X display to use. Note this refers to the X screen abstraction, not the monitor (or output).
I can’t find anything that works.
And, FWIW, there’s no Screensaver config applet in the Settings Manager (at least not that I can find), so you fire it up from the command line:
Yes, you use the Gnome screensaver preferences in Xubuntu.