What determines whether a partial TeX upgrade can be safely resumed?

Answer

The upgrade can be resumed safely only when the package manager’s transaction log shows that every requested package action finished successfully and the filename database (ls‑R) has been rebuilt to match the installed tree.

Confirmed facts

• If tlmgr stopped before fmtutil‑sys --all or texhash ran, the generated fmt files may be missing or outdated.
• Running fmtutil‑sys --all after a consistent tree restores the correct format set.
• tlmgr --force reinstalls packages and overwrites conflicting files, but it does not automatically restore user‑added class or hyphenation files that reside in TEXMFLOCAL.

Likely explanation

The package manager keeps a transaction log (tlmgr.log) that records each install/upgrade step. When the log ends with a line indicating a successful package action for every intended upgrade, the internal state is clean and the only remaining work is to rebuild the filename database and format files. If the log is truncated or ends with an error, the tree is partially written and resuming without a full reinstall risks mixing old and new binaries, which can cause silent typesetting failures.

Steps to verify and resume

1. Inspect the end of tlmgr.log (usually TEXMFVAR/web2c/tlmgr/log/tlmgr.log) for a line that reports a successful action for all packages in the upgrade.
2. If the log is clean, run tlmgr update --self --all (or tlmgr install ) to finish any remaining actions.
3. Run texhash to rebuild the filename database (ls‑R).
4. Run fmtutil‑sys --all to regenerate all format files.
5. Compile a minimal test document, e.g. \documentclass{article}\begin{document}Hello\end{document}, and verify no “missing format” errors appear.

Missing diagnostic detail that changes the recommendation

Do you have any locally added format files, custom class files, or hyphenation patterns in TEXMFLOCAL that share names with upgraded packages? If such files exist, a forced reinstall (tlmgr --force) could overwrite them, so you should back up TEXMFLOCAL before proceeding.