I've had this issue with every version of Ubuntu I've tried over the past 8 years, whether running LXDE, Unity or XFCE. Currently I'm running 17.04 with XFCE on a Dell Precision 7510 with a dock, and I've always had various Dell laptops.
Preconditions
At first monitors turn off correctly, either after configured timeout or if I issue xset dpms force off (which I have on a hotkey). After a while (a few days of uptime) that no longer works, probably as a consequence of running some applications that force the monitors to stay on (vlc, yousician, chrome: youtube, etc). The problem does not occur the first time I run them, but will happen after a while, even though the offending applications are no longer running. Rebooting makes things work again, for a while, but is rather inconvenient (I normally reboot every 3-6 months).
Problem:
Once the above happens, the Screens stay on forever. After issuing xset dpms force off, the monitor backlights turn off for a second or two, then come right back on. Same results with xset s activate .
Diagnostics:
$ xset q
Keyboard Control:
auto repeat: on key click percent: 0 LED mask: 00000000
XKB indicators:
00: Caps Lock: off 01: Num Lock: off 02: Scroll Lock: off
03: Compose: off 04: Kana: off 05: Sleep: off
06: Suspend: off 07: Mute: off 08: Misc: off
09: Mail: off 10: Charging: off 11: Shift Lock: off
12: Group 2: off 13: Mouse Keys: off
auto repeat delay: 500 repeat rate: 20
auto repeating keys: 00ffffffdffffbbf
fa9fffefffedffff
9fffffffffffffff
fff7ffffffffffff
bell percent: 50 bell pitch: 400 bell duration: 100
Pointer Control:
acceleration: 10/1 threshold: 3
Screen Saver:
prefer blanking: yes allow exposures: yes
timeout: 0 cycle: 0
Colors:
default colormap: 0x20 BlackPixel: 0x0 WhitePixel: 0xffffff
Font Path:
/usr/share/fonts/X11/misc,/usr/share/fonts/X11/Type1,built-ins
DPMS (Energy Star):
Standby: 720 Suspend: 0 Off: 900
DPMS is Enabled
Monitor is On
Question
What can I do to clear this "stay on" condition without rebooting?
