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I'm facing a kind of a mysterious problem.

We have a PC with Debian 8 installed. It boots fine and works well, unless I try to boot it wihout a display. So, I shutdown the PC, unplug display and then boot the PC again. After that I try to plug the display on and nothing happens - display not working, it just shows the "No signal detected" message.

But that's not all of the mystery: if I boot the PC without a display, its network card also does not get started. Yes, without a display, the network card is not working. If I try to plug a display after the PC has booted, network card and display are not working either. If I boot the PC with a display plugged, both display and network card are working. If I unplg the display after the OS has started, the network card continues to work and once I plug the display back, it also works.

We actually have a set of identical PCs (entirely identical) and they all have the same behavior. I've installed Windows on one of them, the problem has gone, no matter when I plug a display, everything works fine.

What have I done:

  • installed CentOS 6 - still no luck
  • removed acpid from CentOS - no luck
  • disabled acpi entirely using this tutorial - apparently, no luck.

Display is connected with a DVI port, if that matters.

Have anyone faced the same problem?

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I use SUSE (SLES) linux and have encountered a similiar problem. In my case it has to do with /etc/X11/xorg.conf which is where the graphics drivers start... this file then points to the rest of what's needed for graphics whether it's an nvidia graphics card on a pcie slot or onboard graphics on the motherboard/cpu.

I have found that when using a nvidia card, and the nvidia graphics drivers for linux are installed, and i am using a white dvi port for connection, that linux needs to have the monitor connected prior to & during boot for everything to come up clean and without error. If the monitor is not connected and your xorg.conf file is saying to check for monitor, there will be an error preventing you from entering run level 5 successfully.

In your case if the network setup happens after the graphic setup, then this would cause the problem you describe. But normally i've always seen the graphics, such as gdm, happen last in the boot process. Realize if you set usedisplaydevice none in xorg.conf then you will have no console monitor once booted, and you will need network capability to access your computer. If you don't have network capability then you will be forced to hard reset and boot in linux single mode (runlevel 1) so you can edit xorg.conf and comment out usedisplaydevice none

in xorg.conf:

Section "Screen"
    Identifier     "Screen0"
    Device         "Device0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "NoLogo" "True"
#    Option         "UseDisplayDevice" "None"
    SubSection     "Display"
        Depth       24
    EndSubSection

you can try adding the usedisplaydevice line. when it is not commented out with a # then if your monitor is the problem this may help and get you into runlevel 5 and have the network card activated.

In any case, you should scour the boot.msg file showing everything that happens during boot. That's where you'll find warnings/errors that will give you a clue as to what is happening.

You may also try editting etc/inittab mine has this line in the beginning

# The default runlevel is defined here
id:5:initdefault:

if centos works the same way, then that id:5 means boot to run level 5 == full networking and graphics. You can try changing that 5 to a 3, where runlevel 3 stops short of graphics and gives you a simple console on your entire monitor screen; and have UseDisplayDevice None in xorg.conf commented out if you do this.

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