[Bug 1836782] Re: "ubi-partman failed with exit code 10" when stepping back and forward over partitioning screen

[Steve Langasek]

** Also affects: ubiquity (Ubuntu Eoan)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1836782

Title:
  "ubi-partman failed with exit code 10" when stepping back and forward
  over partitioning screen

Status in ubiquity package in Ubuntu:
  New
Status in ubiquity source package in Eoan:
  New

Bug description:
  I started an Ubuntu 19.04 amd64 Desktop UEFI installation(running
  under Virtualbox 6.0.8 on an Ubuntu 18.04.2 amd64 host) with default
  settings. I chose automatic partitioning, confirmed this installation
  screen, confirmed the popup prompt about writing changes to disk, then
  the timezone screen was shown and the installer started copying files
  to the installation target.

  At this point, the installer now (I *think* (but have not tested) this was not present in the 18.04.2 installer) allows you to go "back", returning you to the partitioning screen, where you could select a different partitioning scheme. While the installer kept copying files in the background, I just kept the previous settings and clicked 'Next' to return to the timezone selection screen. At this point, an error message
    "ubi-partman failed with exit code 10"
  was shown. This will be a result of the installer failing to update the partition table of the target since there are currently mounted file systems on it where it is copying files to.

  If this message is confirmed and the rest of the installation screens are completed, and the installer finishes copying files, it will fail while running grub, showing the following message:
    "Unable to install GRUB to /dev/sda"
    "Executing 'prub-install /dev/sda' failed."
    "This is a fatal error."

  I would think the "back" button on the timezone selection screen needs
  to be disabled so that changing the installation type and partitioning
  is not possible after the installer has started copying files. This
  appears to be a logical error, I assume log files are not required.
  Please state so if you still need them.

  This affects both Ubuntu 19.04 and Kubuntu 19.04 amd64 Desktop UEFI
  installations.

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