[Bug 1491894] Re: lucid to precise to trusty upgrade may leave system unbootable

[Louis Bouchard]

I have the feeling that this portion of the grub-pc.postinst script is
causing the issue :

            db_get grub-pc/install_devices
            if [ -z "$RET" ]; then
              # Reset the seen flag if the current answer is false, since
              # otherwise we'll loop with no indication of why.
              db_get grub-pc/install_devices_empty
              if [ "$RET" = false ]; then
                db_fset grub-pc/install_devices_empty seen false
              fi
              if db_input critical grub-pc/install_devices_empty; then
                db_go
                db_get grub-pc/install_devices_empty
                if [ "$RET" = true ]; then
                  break
                else
                  db_fset "$question" seen false
                  db_fset grub-pc/install_devices_empty seen false
                fi
              else
                break # noninteractive
              fi
            else
              break
            fi

Here is the debug log of a normal (i.e. failed) update :

debconf (developer): starting /var/lib/dpkg/info/grub-pc.postinst configure 1.99-21ubuntu3.18
...
debconf (developer): <-- INPUT high grub-pc/install_devices
debconf (developer): --> 30 question skipped
debconf (developer): <-- GO 
debconf (developer): --> 0 ok
debconf (developer): <-- GET grub-pc/install_devices
debconf (developer): --> 0 
debconf (developer): <-- GET grub-pc/install_devices
debconf (developer): --> 0 
debconf (developer): <-- GET grub-pc/install_devices_empty
debconf (developer): --> 0 true
debconf (developer): <-- INPUT critical grub-pc/install_devices_empty
debconf (developer): --> 30 question skipped

When install_devices_empty = true, no question is asked and so no chance
of fixing grub

When changing install_devices_empty to false we get :

debconf (developer): starting /var/lib/dpkg/info/grub-pc.postinst configure 1.99-21ubuntu3.18
....
debconf (developer): <-- INPUT high grub-pc/install_devices                      
debconf (developer): --> 30 question skipped                                     
debconf (developer): <-- GO                                                      
debconf (developer): --> 0 ok                                                    
debconf (developer): <-- GET grub-pc/install_devices                             
debconf (developer): --> 0                                                       
debconf (developer): <-- GET grub-pc/install_devices                             
debconf (developer): --> 0                                                       
debconf (developer): <-- GET grub-pc/install_devices_empty                       
debconf (developer): --> 0 false                                                 
debconf (developer): <-- FSET grub-pc/install_devices_empty seen false           
debconf (developer): --> 0 false                                                 
debconf (developer): <-- INPUT critical grub-pc/install_devices_empty            
debconf (developer): --> 0 question will be asked                                
debconf (developer): <-- GO

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https://bugs.launchpad.net/bugs/1491894

Title:
  lucid to precise to trusty upgrade may leave system unbootable

Status in grub2 package in Ubuntu:
  Confirmed

Bug description:
  A system, initially installed on 10.04 Lucid then upgraded to 12.04
  precise, when upgraded to Trusty may not reboot following the end of
  the do-release-upgrade command.

  Reproduction steps
  ==================

  Install a VM with 10.04.4-server ISO. When booted in 10.04, issue :

  $ sudo do-release-upgrade           # to 12.04 precise

  Then let the system upgrade and reboot.

  $ sudo do-release-upgrade           # to 14.04 trusty

  Then let the system upgrade and reboot

  Upon reboot, the system will display a blank screen with a prompt and
  will not reboot.

  Workaround
  ==========

  Force a reconfiguration of the grub-pc package :
  $ sudo dpkg-reconfigure grub-pc

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