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    [SOLVED] Boot to black after upgrade

    Hi. This morning I upgraded to 19.10, and I've spent all day trying to troubleshoot a boot problem, so at this point I could use some help.

    I'm running Kubuntu on a MacBook Pro (Late 2008), single-boot via GRUB. This laptop has two NVIDIA graphics processors, and I've been using the NVIDIA proprietary drivers, which are listed as the recommended drivers in system settings. I recall also having trouble booting soon after I first installed Kubuntu on this machine, a year and a half to two years ago, and switched from the default Nouveau open-source driver to the NVIDIA driver. Unfortunately I can't recall what I did at that time to fix the problem.

    Potentially complicating the problem now is that sometime within the last month or so, in Muon, in the Software Sources window, I deleted what I assumed were some unnecessary old software signing keys. I was able to continue doing regular updates, but the new Kubuntu release failed with authentication errors until I figured out to reinstall the package containing the repository signing keys.

    After I did that, the Kubuntu upgrade proceeded apparently normally through the download of almost all of the packages. I stepped away to do other things, and when next I checked, the screen was blank. I left it a while longer, and when I felt confident nothing more was going to happen, I powered it down and back up again.

    Now when I start the laptop, I see the GRUB screen, followed by the usual disk encryption password entry screen. I enter the encryption password and see the success confirmation. Then the screen goes to black, with no backlight, and stays black until I cycle the power.

    Alternatively, if on the GRUB screen I choose one of the recovery mode options, then I get a bunch of text output, which stops to prompt for the encryption password, then continues for a while before the screen again goes black and stays that way.

    I videoed this process and made a screenshot of the text just before the screen goes black, but here on the Post New Thread screen, under Posting Permissions, it says "You may not post attachments". So I will have to just tell you that the last two lines, which seem like the ones most likely to be helpful, are:


    [ OK ] Started Load/Save Screen Backlight Brightness of leds:smc:kbd_backlight.
    [ 52.453471 ] PKCS#7 signature not signed with a trusted key


    I'm thinking that either something in the upgrade broke the graphics driver, or one of the repository signing keys I deleted recently is still not fixed. Or both.

    I'm thinking maybe I need to switch back to the Nouveau driver? And/or, maybe I need to reinstall some other software signing key(s)? I've tried a few GRUB parameter edits to try to boot into a text terminal, but so far I always just keep going to black at the same point.

    So I'd appreciate any advice about how to get booted again, either to the desktop or even just to a terminal, or any other ideas about how to proceed.

    Thank you!

    #2
    Update: I had a spare hard disk drive with OS X on it and plenty of space for another operating system, so I put a fresh Kubuntu on that disk and am now using that one, which after I installed the NVIDIA driver also booted to black. So that rules out the repository keys I deleted pre-upgrade as the cause.

    Using a Kubuntu live USB and some fancy mount-ing and chroot-ing, I managed to remove the NVIDIA driver. Now I'm up and running yet again ... but KMail crashes. Which I expected, since I've experienced the same problem in the past with the nouveau graphics driver. It seems to be a well-known issue, with developers arguing for years over whose responsibility it is, so I don't expect a fix or work-around anytime soon.

    I would like to continue using KMail. Therefore, since it and the NVIDIA graphics driver were working for me before I upgraded Kubuntu, getting the NVIDIA driver working again seems like the more fruitful avenue to pursue. I don't think there's been any change to the driver. I will continue researching possible changes to boot configuration or kernel module signing, and I would still welcome any other ideas.

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      #3
      Update 2: I seem to have solved my own problem, though I don't exactly know how. After some more reading and research, I decided to try installing the nvidia-340 package again so that I could more carefully scrutinize the logs for whatever they might tell me. Lo and behold: I got a login screen. And now here I am. And I've done some email processing in KMail without any crashes.

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