An application can launch successfully while lacking a current source for future APT updates. This can happen after repository changes, a release transition or a manual .deb installation. A routine update reporting nothing new does not identify every installed program's maintenance path.

Build a focused inventory

On the Ubuntu computer, use apt list '?obsolete' to list installed packages that are not referenced by the currently configured archives. The quotation marks keep the query together for APT. Treat the result as a review list, not an automatic removal instruction.

For each application you still depend on, record its package name, installed version, purpose and who supplied it. Ask the person who maintains the machine about intentionally local packages. Some entries may be deliberate internal software; others may belong to a third-party repository that was disabled or removed.

Compare the publisher's current supported distribution method with the machine's configuration. A manually installed .deb can receive updates when a suitable version is available from a configured source. Without such a source, the normal APT update path may not cover it. A version taken from a newer or testing release can also sit above the versions offered for the installed release.

Assign a maintenance decision

For software still needed, agree how its updates will be obtained and verified. That might involve correcting a supported repository or replacing an abandoned application through a documented migration. Preserve required data and settings before changing the installed package.

For software no longer needed, review its dependencies and removal consequences before uninstalling it. Do not pipe the entire obsolete list into a removal command: absence from an archive does not tell you whether the business still relies on the program.

Finish with a short inventory showing each required application's supported update source or an explicitly owned exception. Recheck the query after source changes, and test the actual application workflow after any replacement. This makes the update gap visible without pretending that a clean list alone proves all software is maintained.

Sources: Ubuntu documentation, Ubuntu documentation.