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I have an embedded board with a small UPS. When AC power goes down, I need to turn off all power hungry devices in order to have a clean shutdown. First thing I do, is set DPMS to force powerdown, then go through the usual SIGTERM/SIGKILL/umount sequence. I have an Intel i915 Display adapter connected to an LVDS LCD panel.

Unfortunately, when Xorg dies, Xserver or the VT code turn the LCD panel back on.

I even tried working around it by directly poking the panel enable register in the Display chip, so that X doesn't know about it, but the panel goes back on when the VT comes back.

Is there any "legal" way of keeping the display off?

Thank you

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Just leave Xorg running. Let it die when the system shuts down.

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Don't plug the monitor into the UPS. Or is it a device with an embedded screen? For turning off the display from a VT, you may find vbetool useful.

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Yes, it's a device with an embedded screen. Yes, I used the vbetool to turn off the display immediately after the X server exits, but I need to avoid even the brief flicker which happens, since it's going to drain a lot of power. – Metiu Mar 20 '10 at 6:28
    
Perhaps you can simply not kill Xorg until after all the critical stuff like unmounting filesystems. You might have to do a lazy unmount, then kill Xorg and hope that the bits make it to disk (or flash) before the power runs out. – Ryan Thompson Apr 16 '10 at 19:19

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