display port suddenly not detected

[displaynope]

Everything was going fine with my install of Kubuntu, but today I turned the monitor off and back on again and now it says that it is not getting a signal from the display port. I have no idea why this happened. I can get to the login page and I can login as guest, but I can't log in as my primary user. It goes from the login page to the first part of logging in and then the monitor dies and it says no signal from display port again. I think the problem has to do with my previous session, but I don't know how I can exit the session without having a graphical desktop. I have come to hate sessions with desktop environments, and I fear I may be stuck in a situation that is impossible to fix.

It switches to HDMI input, but I never installed that driver and the screen is so poorly rendered and jittery that I can't possibly use it. If I logout of my main account the screen goes blank again and says no input from HDMI, and then it goes back to display port and correctly renders the login screen. I am using intel 4600 graphics. I don't have any idea what could have caused this to happen, I didn't make any changes to drivers or anything. All that I did was turn the monitor off and back on, and it hasn't been able to get signal from the intel graphics card ever since. I hope I don't need to reinstall and reconfigure everything all over again.

[Robtygart]

At your login screen is there an option to login as "Failsafe"? Try that and see if you can login and change your session settings.

[displaynope]

update: too much is broken I am going to reinstall.

[Robtygart]

Try truning off your effects and see what happens, Ctrl+Alt+F12. That should stop any openGL stuff.

[displaynope]

Well this is a persistent problem. I did a fresh install and decided to test it, turning my monitor off and on again caused the same exact problem to happen again. At first everything works fine, it doesn't care that I have display port and HDMI up to the first time I turn my monitor off and back on again. After doing that once it is impossible to login to my main account with both cables plugged in, it doesn't detect a signal from display port and the signal from HDMI is too corrupted to be able to do anything. This persists across reboots. The first time this happened it actually seemed to make all of my fonts tiny and mess my desktop settings up in weird ways, but this time it seems to work okay as long as I don't have the HDMI cable plugged in. I don't notice anything broken this time, and I can plug the HDMI cable back in after it logs me in. I need to unplug it during the login though, and I can't power cycle my monitor with both cables plugged in.

I have never faced a problem like this before and I don't even know where to start with it. I didn't realize power cycling my monitor could trigger a bug like this! I am open to any suggestions as to how I can keep both cables plugged in during login, I don't want to need to manually pull the HDMI cable out before every login only to insert it again right afterwards.

If I plug them both in after logging in it works to get input from display port, if I go to display configuration it detects the display port and HDMI input but it has HDMI grayed out. If I enable HDMI the issue happens again and I am forced to reboot and pull the HDMI cable to login again. Even if I leave the HDMI display grayed out I can't login to my main account with the HDMI cable plugged in. I actually disabled the HDMI display myself because my mouse cursor was getting lost off the side of the screen, and applications were opening to the side of my monitor instead of in the center. I had to drag the applications to the center by moving my mouse off to the side and getting lucky. Disabling the HDMI display fixed this and all of my applications started opening in the center of the monitor, and my mouse couldn't get lost to the side of the screen anymore. This was working great up to the point that I power cycled my monitor, now even with HDMI grayed out I can't get a signal from display port if the HDMI cable is plugged in during the login process.

I don't need to use the HDMI connection for my Linux host, I am going to pass it to a Windows VM and use the display port from my onboard graphics card for Linux. But I do need to be able to boot into my Linux host with the HDMI cable plugged in, it is a pretty big pain to have to pull it out and plug it back in again after I login.

update: logging into guest with both plugged in still works, and once again my mouse goes off the side of the screen. When I go into display configuration it shows an HDMI input display to the left of a display port input display, but I only have one monitor. The monitor has onboard intel graphics plugged into the display port and a discrete graphics card plugged into HDMI. I am apparently on the display to the right, as my mouse can get lost to the left and applications open to the left off of my monitor. I can drag opened applications to my monitor by letting the mouse go to the left off of my display. I power cycled my monitor as guest and now it can't detect my display port signal either, and now I need to reboot again.

[Robtygart]

What version of Kubuntu are you trying to install, 13.10? If so have you looked at 12.04?

[oshunluvr]

I'm lost as to what you are trying to accomplish. What the reason to have both cables connected at once? What problem are you trying to solve?

Your mouse goes "off screen" likely because with both cables detected as connected, the system thinks you have two monitors connected. If your idea is to use one output for the linux host and one for the windows VM but on the same monitor, you've got some configuration work ahead of you. This is not a standard configuration by any means. With both connected, run xrandr -q in a terminal and I have little doubt it will show two connected monitors - as it should.

I also assume you've not written a detailed xorg.conf file so xorg is left to it's own detection methods - which usually work fine at boot time but not as well when swapping things about sort of willy-nilly.

[displaynope]

The problem I am trying to solve is being able to switch between a Kubuntu host and a Windows VM. This is becoming a standard configuration for Linux gamers thanks to VT-d technology, a Windows guest can be given direct access to a secondary graphics card. This allows the user to use the Windows VM to play games with a minimal performance penalty. The typical configuration is to use on board graphics for the Linux host while passing a discrete card to the Windows VM with VT-d. Usually you will want to pass a PCI USB card to the Windows guest, in addition to the graphics card. Then you can change your monitors input source to switch between Linux and Windows, and you can use a USB switch to move your mouse and keyboard between the Linux host and the Windows VM. This allows you to simultaneously boot Windows and Linux with only a small performance penalty.

There are tutorials for doing this with Mint and Debian, I can't find any for Ubuntu though. The problem that I am running into is that having both graphics cards plugged in to my monitor at the same time is confusing Ubuntu. I don't mind if it thinks I have two monitors, and this is what it was doing at first. I can disable the discrete graphics input display in display manager and then it acts like I only have one monitor hooked up to the on board graphics. The problem is that this only works up to the first time I power cycle my monitor. If I power cycle my monitor Kubuntu can never again get signal from the display port with the HDMI cable plugged in. I think it is a bug because it appears to work correctly at first but then has problems when I power cycle the monitor.

[oshunluvr]

Ok, so you're using an on-board Intel graphics processor and a PCI nVidia or AMD/ATI card simultaneously but attached to the same monitor using different ports?

Ok, I get why you might want to do that, so why are you turning the monitor on and off? DPMS should be able to switch the monitor to power save mode without punching the power button.

If there's some reason you need to do that, you might have to restart your graphics as well. I've never messed with a display port or hdmi this way (powering on and off) so I can't speak to why this is happening. Some web searching reveals this is common when using hdmi/display port. That is to say powering off the monitor causes these ports to disappear from detection. Not surprising actually as these are "smarter" ports than VGA or HDMI. It called "Display Port Blanking" and is causing a lot of headaches with Windows users.