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A major problem solved

Here's one for your cheat sheet.

If you're reading this, I'm succressfully back up on my e-mail after a very serious -- and unexpected -- Fedora 30 failure on my laptop on August 26. When one makes a change to the video display settings, Fedora shouldn't blow up. But that's exactly what it did.

I have a 4K display on my ThinkPad P72 driven by an Nvidia Quadro P5000 mobile graphics card. It defaults to a 60 fps refresh rate with the MATE desktop, but there's a 120 fps option in Monitor Preferences. I thought changing that might be an interesting test, but as soon as I hit the Apply button my video vanished completely. I rebooted thinking it would recover. Nope. Fedora would not boot to anything other than single user mode. Nothing I tried could bring it back to life. Steve suggested trying xrandr, but that won't run in text mode.

After days of hunting for a fix, I gave up and bought a new 4T notebook drive and an external SATA "toaster" adapter. I used ddrescue to make forensic backups of the four F30 partitions to the external SSD. I re-installed a F30 Workstation image and ran "yum update" to get a generic system.

Fortunately a while back (with Steve's help) I'd created the following utility script in /usr/local/bin:

# cat rpmlist-stripper.sh
#! /bin/sh

# This one-liner will generate an alphabized list of RPM packages for use
# by a for loop to install the exact same packages on another instance.

rpm -qa --qf "%{n}.%{arch}\n" | sort > $1

# end-of-file

Using this file in a yum 'for' loop, I was able to restore all of the rpms that had been in the crashed system. There were a couple of dozen other little things that needed to be done, but by this evening I decided to look for an easier way if this ever happens again. And I found it:

Sure enough, I found /etc/mate-settings-daemon/xrandr/monitors.xml in the backup of the root filesystem. In it I found the smoking gun:

# cat monitors.xml 
<monitors version="1">
      <output name="eDP-1">
      <output name="HDMI-1">
      <output name="DP-1">
      <output name="DP-2">
      <output name="DP-3">

Had I known where it was two weeks ago, I could have edited that <rate> line back to 60 in single user mode. The thread suggests all that's needed is to delete that file and reboot. Without it, GNOME will start using its defaults.


P.S. That 4T SSD is now installed in my laptop as bulk storage.