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I have Xubuntu 14.04 installed on two PCs, each has its own monitor, different brands.

With both PCs, if I turn off the monitor by power switch, turning it on does not work. In other words, when I turn them on, even after few seconds, they say there is no video signal coming from the PCs.

Why this happens?

Thanks a lot.

EDIT: I installed KDE plasma desktop along with KDE power manager. Nothing changed. I if turn off my monitor, I have to ssh on my system from another machine and reboot it...

EDIT 2: Look what I've found in kern.log:

Feb 24 06:09:47 fuji kernel: [ 1190.076641] [drm:intel_dp_start_link_train] *ERROR* too many voltage retries, give up
Feb 24 06:09:47 fuji kernel: [ 1190.076842] [drm:intel_dp_complete_link_train] *ERROR* failed to train DP, aborting
Feb 24 06:09:47 fuji kernel: [ 1195.355350] video LNXVIDEO:00: Restoring backlight state
Feb 24 06:09:48 fuji kernel: [ 1196.586083] [drm:intel_dp_i2c_aux_ch] *ERROR* too many retries, giving up

While in syslog i found something like:

Feb 24 19:54:39 fuji kernel: [    0.818294] intel_idle: lapic_timer_reliable_states 0xffffffff
Feb 24 19:54:39 fuji kernel: [    1.958366] fb: conflicting fb hw usage inteldrmfb vs VESA VGA - removing generic driver
Feb 24 19:54:39 fuji kernel: [    2.004978] [drm:intel_dp_i2c_aux_ch] *ERROR* too many retries,giving up
Feb 24 19:54:39 fuji kernel: [    2.011007] [drm:intel_dp_i2c_aux_ch] *ERROR* too many retries,giving up
Feb 24 19:54:39 fuji kernel: [    2.782239] fbcon: inteldrmfb (fb0) is primary device
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  • It may be the bug in the new screen locker in XFCE. Unfortunately I can't remember its name but you can find it in the settings menu. You can uninstall it and install xscreensaver. You can also just disable the screensaver but this way your session won't be "locked" after wakeup.
    – Reza
    Feb 23, 2015 at 11:08
  • It is called lightlocker. Uninstalled, but with no luck. If I turn off display, it stays dead :(
    – MadHatter
    Feb 23, 2015 at 22:15
  • Have you tried turning off all power settings on the monitor itself? (as you use manual power-off...)
    – Fabby
    Feb 26, 2015 at 9:29
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    I think Fabby is right. This isn't the sort of thing that Ubuntu controls. WHether or not the monitor will come back on is controlled by the monitor and not by Ubuntu.
    – John Scott
    Feb 27, 2015 at 1:12
  • Have you tried Ctrl+Alt+F2 followed by Ctrl+Alt+F7? See if it fix it temporary
    – kos
    Feb 27, 2015 at 14:09

1 Answer 1

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It is a kernel bug, limited to monitors connected via Display Port output to an Intel Integrated Graphics.

I found it googling [drm:intel_dp_i2c_aux_ch] *ERROR* too many retries,giving up

However, this bug has been fixed in Linux 3.16, which can be installed in Ubuntu 14.04. If you are running 14.10, you already have this kernel and you should not have to do this. You also have 3.16 if you have installed Ubuntu 14.04 from a 14.04.2 installation disk. It does not matter whether or not you are using Ubuntu 14.04.2 or not (which you are if you have been staying up-to-date), but if you used a 14.04.2 DVD or flash drive to do the installation. If you installed Ubuntu 14.04 with a 14.04 or 14.04.1 installation disk, there is a solution, which is explained below.

Linux 3.16 is available as an HWE kernel, a kernel that is designed for Ubuntu LTS users to get better hardware support, but it also fixes some bugs. However, I will warn you, that if you have been using Ubuntu for a while and have lots of different programs installed on your system, then you are at a small risk of experiencing minor bugs, such as an application having slightly unusual behavior. It is best to follow these steps just after doing a fresh install of 14.04 or 14.04.1. (Again, I can't say this enough, but don't do this with a 14.04.2 disk.)

Now, let's get started. Open up a terminal and run the command sudo apt-get update && sudo apt-get install linux-hwe-generic-trusty. This will install Linux 3.16 and it's kernel headers for you. Now, prepare to test the new kernel! Reboot your system, and your computer should boot into Linux 3.16. The bug should be fixed, and all should be well now. If they are, skip the next paragraph on troubleshooting.

If the above worked for you, great. Move to the next paragraph. If it didn't, gave some unusual errors, prevented you from logging in, or had some other bizarre behavior, you need to reboot your system and remove the kernel. Hold down Shift as your system boots (no need if you dual-boot with GRUB!) and choose "Advanced options" or something similar. Choose the newest Linux 3.13 (recovery mode) and boot that. Choose to get to a root shell or terminal (again, could say something different), and let it load. Then, you must enter the command mount -o remount,rw / to make your filesystem writeable. If you have multiple partitions for your filesystem, you must also run mount --all afterwards. (If you're unsure if you do or not, run it anyway.) Then run apt-get purge linux-hwe-generic-trusty && apt-get autoremove. Reboot your system, and skip the next paragraph (it is meant for those that got the kernel to work).

If you didn't get the kernel to work, skip tot he next paragraph. If you did, you must be lucky, as it makes this much easier. As you now have Linux 3.16 working well, you can remove 3.13 to free yourself some disk space. Run the command sudo apt-get remove linux-generic linux-image-3.13* && sudo apt-get autoremove. You should be able to reboot your computer and it will still work fine.

Okay, I hope that helped you. If you never got the kernel to work and followed my directions for removing it, you need to backup your files and re-install. It's the best way. However, make sure you use an Ubuntu 14.04.2 or newer installation disk this time! (If you have a 14.04 or 14.04.1 disk, don't think you can just install that and follow my directions. Believe me, it's just better to create a new disk and install 14.04.2. Then you won't have to follow my directions at all!)

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    Would you mind giving a link to the bug report? Also, have you tried the HWE kernel?
    – John Scott
    Feb 27, 2015 at 23:05
  • For example, bbs.archlinux.org/viewtopic.php?id=184918. Besides, I didn't try the HWE. I am afraid of making mess with such an important stuff.. Do you think the HWE kernel is worth a try? Thanks.
    – MadHatter
    Feb 28, 2015 at 0:06
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    The HWE kernel is definitely worth the try. It upgrades you to Linux 3.16, after all! 3.16 offers so many new hardware enhancements that it is shipping with Ubuntu 14.04 from this point forward. Run 'sudo apt-get install linux-hwe-generic-trusty' and reboot. If it doesn't work, boot with an older kernel and remove the package.
    – John Scott
    Feb 28, 2015 at 5:23
  • I installed the HWE kernel, and I'm testing it. Thanks for your advice. There is a problem, though. When I run dist-upgrade, it wants o install again the 3.13 kernel.. How may I force it to retain 3.16 HWE? Thanks again...
    – MadHatter
    Feb 28, 2015 at 16:08
  • You can have both the HWE kernel installed and the original kernel if you want. (It will automatically boot to HWE.) That 'install again the 3.13 kernel' you are mentioning is just an update for it. (You've had the 3.13 kernel from the start and it's not a bad thing that you have it installed. It's not 'installing again', it's just an update.) If you want to remove the original 3.13 kernel because you don't need it anymore, run 'sudo apt-get remove linux-image-generic && sudo apt-get autoremove'.
    – John Scott
    Feb 28, 2015 at 16:57

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