Comment 0 for bug 2063268

unattended-upgrades will fail if a package has a conffile prompt. This is unusual for a new install, but recently became an issue for me because of changes to the ubuntu-advantage-tools packages. Specifically, uu logged issues with the package ubuntu-pro-client.

In older versions of subiquity, unattended-upgrades failing causes subiquity to crash and the install to fail. That no longer appears to be case in newer releases of subiquity. I think because of this commit
https://github.com/canonical/subiquity/commit/800a1e9372f23591b504afa211da7e3cbe30b788

According to the unattended-upgrades source a failure is expected if a package has a conffile prompt. Based on the comment at https://github.com/mvo5/unattended-upgrades/blob/7bf3aa52af1c6b11c031d0949f223c1beb94f84c/unattended-upgrade#L2597

    # Was the overall run succesful: only if everything installed
    # fine and nothing was held back because of a conffile prompt.

A potential simple solution would be to append to /etc/apt/apt.conf.d/zzzz-temp-installer-unattended-upgrade
Dpkg::Options::="--force-confold"

An argument could be made for "--force-confnew" instead, but subiquity is already using "--force-confold" when installing packages individually.
https://github.com/canonical/subiquity/blob/dbcf72367606559e7dae530197e4e0694afa63d3/subiquity/server/pkghelper.py#L84

I believe this will work because the unattended-upgrades source checks for these options and will not "blacklist" any upgrades if present. However, I have not tested to verify.
https://github.com/mvo5/unattended-upgrades/blob/7bf3aa52af1c6b11c031d0949f223c1beb94f84c/unattended-upgrade#L1536

These are some of the logs generated by subiquity when uu fails during an Ubuntu 22.04 install.

Apr 12 22:19:36 ubuntu-server subiquity_log.1234[10785]: check_conffile_prompt(/var/cache/apt/archives/ubuntu-pro-client_31.2~22.04_amd64.deb)
Apr 12 22:19:36 ubuntu-server subiquity_log.1234[10785]: Package ubuntu-pro-client has conffile prompt and needs to be upgraded manually
Apr 12 22:19:36 ubuntu-server subiquity_log.1234[10785]: Package ubuntu-pro-client has conffile prompt and needs to be upgraded manually
...
Apr 12 22:19:37 ubuntu-server subiquity_log.1234[10785]: Packages blacklist due to conffile prompts: ['ubuntu\\-pro\\-client$']
...
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Packages that are kept back:
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: InstCount=0 DelCount=0 BrokenCount=0
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Package python3-update-manager has a higher version available, checking if it is from an allowed origin and is not pinned down.
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Package python3-update-manager is kept back because a related package is kept back or due to local apt_preferences(5).
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Package ubuntu-advantage-tools has a higher version available, checking if it is from an allowed origin and is not pinned down.
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Package ubuntu-advantage-tools is kept back because a related package is kept back or due to local apt_preferences(5).
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Package update-manager-core has a higher version available, checking if it is from an allowed origin and is not pinned down.
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Package update-manager-core is kept back because a related package is kept back or due to local apt_preferences(5).
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10785]: Extracting content from /var/log/unattended-upgrades/unattended-upgrades-dpkg.log since 2024-04-12 22:18:35
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10774]: Running command ['udevadm', 'settle'] with allowed return codes [0] (capture=False)
...
Apr 12 22:45:55 ubuntu-server subiquity_log.1234[10774]: finish: cmd-in-target: FAIL: curtin command in-target