xfce4-display-settings

[Boris Hollas]

I use xrandr to detect and activate monitors. However, the Xfce window 
manager doesn't always discover that the screen resolution has changed. 
So I tried

~$ xfce4-display-settings --display=DVI-0
xfce4-display-settings: Cannot open display: DVI-0.

although

~$ xrandr -q
Screen 0: minimum 320 x 200, current 1920 x 1200, maximum 8192 x 8192
DVI-0 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 
546mm x 352mm

Also,

~$ xfce4-display-settings --display=LVDS
xfce4-display-settings: Cannot open display: LVDS.

although LVDS is connected.

What is the correct syntax?