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We have up-to-date Debian Jesse boxes configured with Xorg / lightdm / xfce4. They're set up to auto login and run some programs at startup. This normally works just fine.

The problem is when there's no monitor plugged in at boot time (due to KVM switch in wrong position, or simply forgot to plug in monitor cable). Xorg still starts, does not detect a monitor (as expected), and seems to create a frame buffer at a nominal resolution that's not connected to any video outputs. The other processes all start, outputting to that frame buffer. Xorg.0.log shows this:

[    20.650] (II) intel(0): Output VGA1 has no monitor section
[    20.651] (II) intel(0): Output HDMI1 has no monitor section
[    20.651] (II) intel(0): Output DP1 has no monitor section
[    20.652] (II) intel(0): EDID for output VGA1
[    20.653] (II) intel(0): EDID for output HDMI1
[    20.653] (II) intel(0): EDID for output DP1
[    20.653] (II) intel(0): Output VGA1 disconnected
[    20.653] (II) intel(0): Output HDMI1 disconnected
[    20.653] (II) intel(0): Output DP1 disconnected
[    20.653] (WW) intel(0): No outputs definitely connected, trying again...
...
[    20.653] (WW) intel(0): Unable to find connected outputs - setting 1024x768 initial framebuffer
[    20.653] (II) intel(0): Using default gamma of (1.0, 1.0, 1.0) unless otherwise stated.
[    20.653] (II) intel(0): Kernel page flipping support detected, enabling
[    20.653] (==) intel(0): DPI set to (96, 96)

If I now plug in a monitor, it seems to EDID just fine, but the video output remains disabled. I can ctrl-alt-F1 to get a text console and log in, but can't figure out how to enable the video output and get the frame buffer attached to it.

xrandr -d :0 --prop says:

Screen 0: minimum 320 x 200, current 320 x 200, maximum 8192 x 8192
VGA1 connected (normal left inverted right x axis y axis)
    EDID: 
        00ffffffffffff0010ac4a40554e4743
        151401030a351e78ea9eb5a259559b25
        0e5054a54b00714f8180d1c001010101
        010101010101023a801871382d40582c
        4500132a2100001e000000ff0031344b
        304e30355043474e550a000000fc0044
        454c4c2047323431300a2020000000fd
        00384c1e5312000a202020202020009b
   1920x1080     60.00 +
   1280x1024     75.02    60.02  
   1152x864      75.00  
   1024x768      75.08    60.00  
   800x600       75.00    60.32  
   640x480       75.00    60.00  
   720x400       70.08  
HDMI1 disconnected (normal left inverted right x axis y axis)
    Broadcast RGB: Automatic 
        supported: Automatic, Full, Limited 16:235
    audio: auto 
        supported: force-dvi, off, auto, on
DP1 disconnected (normal left inverted right x axis y axis)
    Broadcast RGB: Automatic 
        supported: Automatic, Full, Limited 16:235
    audio: auto 
        supported: force-dvi, off, auto, on

So we're seeing the monitor now attached to VGA1. Trying xrandr -d :0 --output VGA1 --auto (and variations with various modeline settings) all result in:

xrandr: Configure crtc 0 failed

I can't figure out what this is trying to tell me...

Two problems / questions:

  1. If there a way to force Xorg to default to enabling the VGA output when no monitors are initially detected, even if it's at a less than ideal resolution?

  2. Failing that, how can I enable the video output once a monitor is plugged in?

Edit: Here's the output from xrandr -d :0 --verbose :

Screen 0: minimum 320 x 200, current 1024 x 768, maximum 8192 x 8192
VGA1 connected (normal left inverted right x axis y axis)
    Identifier: 0x41
    Timestamp:  21055
    Subpixel:   unknown
    Clones:     HDMI1
    CRTCs:      0 1
    Transform:  1.000000 0.000000 0.000000
                0.000000 1.000000 0.000000
                0.000000 0.000000 1.000000
               filter: 
    EDID: 
        00ffffffffffff0010ac4a40554e4743
        151401030a351e78ea9eb5a259559b25
        0e5054a54b00714f8180d1c001010101
        010101010101023a801871382d40582c
        4500132a2100001e000000ff0031344b
        304e30355043474e550a000000fc0044
        454c4c2047323431300a2020000000fd
        00384c1e5312000a202020202020009b
  1920x1080 (0x99) 148.500MHz +HSync +VSync +preferred
        h: width  1920 start 2008 end 2052 total 2200 skew    0 clock  67.50KHz
        v: height 1080 start 1084 end 1089 total 1125           clock  60.00Hz
  1280x1024 (0x9a) 135.000MHz +HSync +VSync
        h: width  1280 start 1296 end 1440 total 1688 skew    0 clock  79.98KHz
        v: height 1024 start 1025 end 1028 total 1066           clock  75.02Hz
  1280x1024 (0x9b) 108.000MHz +HSync +VSync
        h: width  1280 start 1328 end 1440 total 1688 skew    0 clock  63.98KHz
        v: height 1024 start 1025 end 1028 total 1066           clock  60.02Hz
  1152x864 (0x9c) 108.000MHz +HSync +VSync
        h: width  1152 start 1216 end 1344 total 1600 skew    0 clock  67.50KHz
        v: height  864 start  865 end  868 total  900           clock  75.00Hz
  1024x768 (0x9d) 78.800MHz +HSync +VSync
        h: width  1024 start 1040 end 1136 total 1312 skew    0 clock  60.06KHz
        v: height  768 start  769 end  772 total  800           clock  75.08Hz
  1024x768 (0x9e) 65.000MHz -HSync -VSync
        h: width  1024 start 1048 end 1184 total 1344 skew    0 clock  48.36KHz
        v: height  768 start  771 end  777 total  806           clock  60.00Hz
  800x600 (0x9f) 49.500MHz +HSync +VSync
        h: width   800 start  816 end  896 total 1056 skew    0 clock  46.88KHz
        v: height  600 start  601 end  604 total  625           clock  75.00Hz
  800x600 (0xa0) 40.000MHz +HSync +VSync
        h: width   800 start  840 end  968 total 1056 skew    0 clock  37.88KHz
        v: height  600 start  601 end  605 total  628           clock  60.32Hz
  640x480 (0xa1) 31.500MHz -HSync -VSync
        h: width   640 start  656 end  720 total  840 skew    0 clock  37.50KHz
        v: height  480 start  481 end  484 total  500           clock  75.00Hz
  640x480 (0xa2) 25.200MHz -HSync -VSync
        h: width   640 start  656 end  752 total  800 skew    0 clock  31.50KHz
        v: height  480 start  490 end  492 total  525           clock  60.00Hz
  720x400 (0xa3) 28.320MHz -HSync +VSync
        h: width   720 start  738 end  846 total  900 skew    0 clock  31.47KHz
        v: height  400 start  412 end  414 total  449           clock  70.08Hz
HDMI1 disconnected (normal left inverted right x axis y axis)
    Identifier: 0x42
    Timestamp:  21055
    Subpixel:   unknown
    Clones:     VGA1
    CRTCs:      0 1
    Transform:  1.000000 0.000000 0.000000
                0.000000 1.000000 0.000000
                0.000000 0.000000 1.000000
               filter: 
    Broadcast RGB: Automatic 
        supported: Automatic, Full, Limited 16:235
    audio: auto 
        supported: force-dvi, off, auto, on
DP1 disconnected (normal left inverted right x axis y axis)
    Identifier: 0x43
    Timestamp:  21055
    Subpixel:   unknown
    Clones:    
    CRTCs:      0 1
    Transform:  1.000000 0.000000 0.000000
                0.000000 1.000000 0.000000
                0.000000 0.000000 1.000000
               filter: 
    Broadcast RGB: Automatic 
        supported: Automatic, Full, Limited 16:235
    audio: auto 
        supported: force-dvi, off, auto, on
  • Did you red that: unix.stackexchange.com/a/60110/85876 ? – dervishe May 10 '16 at 16:23
  • @dervishe Thanks for the link, but that's not the issue. Monitor detection seems to be working just fine. The problem is that once a monitor is detected how do I enable video driver output to it? (or how to not disable the video output in the first place?) – Mike Blackwell May 10 '16 at 18:06
  • Could you give us the result of xrandr --verbose ? (when the monitor is plugged in) – dervishe May 10 '16 at 18:16
  • Verbose output added to question. – Mike Blackwell May 10 '16 at 19:33
  • did you try the --crtc 1 option with your xrandr config ? something like: xrandr -d :0 --output VGA1 --mode 1920x1080 --crtc 1 and eventually disable each other outputs – dervishe May 10 '16 at 19:40

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