[GTALUG] war story: fixing a Fedora installation that got broken during update

[D. Hugh Redelmeier]

Many people don't update their software.  They claim that it only brings 
grief.  I'm the opposite: I take any update offered in the hope it is an 
improvement.

One of my computers hung during a Fedora update.  I don't know why 
it happened because I wasn't there (I also don't watch paint drying).

Symptom: booting would not get the the log-in screen (GDM?).

Step 1: have booting log to the display

Normally Fedora booting is quiet so as not to disturb the serenity of the 
user.  In this case we want to see the log.  It might tell us what's wrong 
and it might tell us how far it got before hanging.

- at the GRUB boot menu, type "e" to be given the chance to edit the 
  commands that GRUB will execute to boot Linux.

- cursor to the end of the "linux" line

- remove the last two parameters ("rhgb quiet")

- type CTRL-x to get the modified commands executed

Now lots of logging information will scroll by on the screen.

In my particular case, it didn't tell me much but I could see that booting 
got a long way.


Step 2: boot from a live Fedora USB and examine the system's HDD/SSD.

I assume that you know how to boot from a live installation USB flash 
drive.

It is easy from that desktop to examine the broken system.

- SMART scanning the system's disk might by worthwhile, if only to 
  eliminate that source of doubt.

- file system checks are always a good idea

In my particular case, I didn't see anything obvious.

Complicated brain surgery can be done by starting up the broken system in 
a chroot environment.  I started down that road but was interrupted before 
success or failure.


Step 3: boot the system console mode, without a GUI.

This had promise because it looked to me as if the failure was starting 
the graphical system

Proceed like step 1, but after erasing "rhgb quiet", add " 3"; hit CTRL-X.

Log in.  Now you have a shell.

Since the system failed after a software update, I decided to do more of 
them.  You could instead back out of them.

  sudo dnf update

Failure:
There was a set of kernel packages that seemed to be half installed.

I removed the half that was installed and asked again for an update.  It 
worked.

I could reboot the system and it would come up as expected.

Success!