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2.4. XF86Config Tuning

There are essentially two different types of screen blanking that can be performed under X-Windows: BlankTime and DPMS. The first is simply a fake "blanking" effect that doesn't actually save any power. The others are specific only to DPMS-compliant monitors, and must be specifically enabled to take effect. They are located in your XF86Config file, which normally resides in /etc/X11/XF86Config.

DPMS (Display Power Management Signaling) is a standard to reduce power consumption in monitors [2]. Typically, both the monitor and the video card must support the DPMS standard in order to receive any benefit from it. DPMS specifies four modes of operation (in order of increasing power savings): "Normal", "Standby", "Suspend" and "Off". Two signal lines, "Horizontal Sync" and "Vertical Sync" provide a method for signaling these four different states to a DPMS monitor.

If you have a DPMS-compliant monitor, you might want to try enabling support for it under the Monitor section of your XF86Config file:

Section "Monitor"
	[... other values here ...]
	Option	"DPMS"
EndSection

To manipulate the DPMS functions, you can create/modify the following items in the ServerLayout section.

Section "ServerLayout"
	Option "BlankTime"	"10"	# Blank the screen in 10 minutes (Fake)
	Option "StandbyTime" 	"20"	# Turn off screen in 20 minutes (DPMS)
	Option "SuspendTime"	"30"	# Full hibernation in 30 minutes (DPMS)
	Option "OffTime"	"40"	# Turn off DPMS monitor (DPMS)
EndSection

BlankTime is not actually a power saving level at all. The screen is sent a "fake" blanking effect and defaults to activate after 10 minutes. Alternately, it can indicate the number of minutes until the screensaver should activate. It has nothing to do with DPMS.

StandbyTime is a very minor power saving level. This setting usually involves blanking the screen by turning off the electron (RGB) gun. However, the power supply is left on and the tube filaments energized. When you need to use the monitor again, the monitor will come back on very quickly. This option requires DPMS monitor/video-card support and defaults to 20 minutes under X-Windows. Also known as hsync suspend mode, since the horizontal sync signal is turned off to signal this power management state to a DPMS monitor.

SuspendTime is a very strong low power alternative. This setting usually involves the same power conservation as StandbyTime, however in addition the power supply is turned off. This option requires DPMS monitor/video-card support and defaults to 30 minutes under X-Windows. Also known as vsync suspend mode, since the vertical sync signal is turned off to signal this power management state to a DPMS monitor.

OffTime usually means just that. The computer monitor is turned off. A small auxiliary circuit stays on to monitor the signals from the computer to turn the monitor back on when data needs to be displayed to the screen. Obviously, this keeps power consumption to a bare minimum (zero). While the power saving is substantial, to reactivate the monitor may take up to 8-10 seconds. This option requires DPMS monitor/video-card support and defaults to 40 minutes under X-Windows. Both the horizontal and vertical sync signals are turned off to signal this power management state to a DPMS monitor.

After activating your changes and restarting X-Windows, you might want to examine your logfile to see if your video card has any problems with your changes:

$ egrep "^\(WW|EE\)" /var/log/XFree86.0.log

There may be additional options that you can enable for your specific video card/chip driver; see the XFree86 Documentation website for specifics.

Of course, all of this can also be activated "on-the-fly" by using xset(1). If you don't have access to your system's XF86Config file, a good place to put these commands would be in your ~/.Xsession or ~/.xinitrc file.

$ xset -dpms			# Disable DPMS
$ xset +dpms			# Enable DPMS
$ xset s off			# Disable screen blanking
$ xset s 150			# Blank the screen after 150 seconds
$ xset dpms 300 600 900		# Set standby, suspend, & off times (in seconds)
$ xset dpms force standby	# Immediately go into standby mode
$ xset dpms force suspend	# Immediately go into suspend mode
$ xset dpms force off		# Immediately turn off the monitor
$ xset -q			# Query current settings

If instead you're using the Linux console (not X-Windows), you'll want to use setterm(1):

$ setterm -blank 10		# Blank the screen in 10 minutes
$ setterm -powersave on		# Put the monitor into VESA power saving mode
$ setterm -powerdown 20		# Set the VESA powerdown to 20 minutes