agent ran apt upgrade as part of a runtime migration and a debconf prompt froze the whole run with no tty

TL;DR: Tell both layers to stop asking: run the upgrade with the frontend set to noninteractive and answer yes to apt itself. Pre-seed answers for packages you know will ask, and decide the conffile policy (keep or install) up front. A package upgrade in automation must be fully answerable before it starts.

agent ran apt upgrade as part of a runtime migration and a debconf prompt froze the whole run with no tty

1. Confirm the stall is a debconf prompt: the process is idle mid-upgrade, often with a package name visible in the last output lines.

Expected: identifying which package asked tells you what answer it wanted.

1. Kill the hung process and check for a half-configured package: run dpkg --configure -a.

Expected: it finishes configuring any interrupted packages and exits cleanly.

1. Re-run the upgrade non-interactively: set the DEBIAN_FRONTEND environment variable to noninteractive and pass -y to apt-get (use apt-get, not apt, in scripts).

Expected: the upgrade runs to completion with no prompts.

1. For packages that still ask (services asking about restarts, config file changes), pre-seed their answers before upgrading, and set the conffile policy explicitly (keep existing configs or install new ones) via dpkg options.

Expected: a second run on an identical machine asks nothing.

1. Record the exact package set and versions that upgraded in the run log.

Expected: the migration's environment change is auditable and reproducible.

Use this when

• apt upgrade freezes on a configuration prompt in a scripted or agent session
• a runtime migration step stalls mid-package-upgrade with no tty
• debconf questions block an otherwise automated run

Not for this skill when

• apt fails with a dependency or repository error - fix the sources first
• you are upgrading interactively - answer the prompts normally
• the freeze is a locked dpkg database from another process - wait for or stop that process

Variant phrasings

• apt upgrade hangs on debconf prompt in CI
• debconf question freezes headless apt upgrade
• package configuration prompt with no terminal

Why it happens

Some packages ask configuration questions during upgrade through debconf, and debconf's default frontend needs a terminal. With no tty the question cannot be displayed or answered, so the whole upgrade blocks forever. The -y flag only answers apt's own yes/no questions - it does nothing for debconf - which is why runs with -y still freeze: two separate prompting layers, and only one was silenced.

Edge cases

• noninteractive mode makes debconf pick default answers silently - for packages where the default is wrong (mail servers, databases), pre-seed the right answer instead of accepting defaults blindly.
• The conffile decision (keep your config vs install the package's) defaults to keeping yours in noninteractive mode - verify after upgrading services whose behavior depends on new config defaults.
• A frozen upgrade can leave the package database locked - check for and clear stale locks before re-running, after confirming no apt process is alive.
• Kernel or libc upgrades inside a running migration can require a reboot to take effect - schedule the reboot explicitly rather than discovering it later.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstxfrUs6j0hv8YFfFOvoPKg