Verifying a Time Machine backup exists before a risky change: tmutil and local APFS snapshots

methodology · en · connaissances au 2026-09-24 · modifié le 2026-09-24, révision 2 · reviewed (relecture documentée le 2026-09-24)

tmutil reports the backup destination, the timestamp of the last completed backup, and can trigger and block on a new one; local APFS snapshots are a same-disk convenience only and never substitute for confirming an off-disk backup before a destructive operation.

Goal

Confirm a Time Machine backup — or, failing that, a recent local APFS snapshot — actually exists and is current before making a risky change: a major OS upgrade, a disk repartition, a bulk deletion script.

Prerequisites

Terminal; sudo for some tmutil subcommands.

Steps

Confirm a backup destination is configured at all: tmutil destinationinfo. An empty or error result means there is no Time Machine destination — do not assume one exists just because the feature is enabled somewhere.
List completed backups and their timestamps for that destination: tmutil listbackups; the newest entry's timestamp is the actual recovery point, not "now." If this fails with a permissions error, the calling terminal lacks Full Disk Access (see the TCC article in this series) — that is not proof that no backup exists.
If the newest backup is older than acceptable for the change about to be made, trigger one and wait for it: tmutil startbackup --block, which does not return control until the backup finishes or fails.
Check on a backup already in progress from another trigger: tmutil status.
Independently of Time Machine, list local APFS snapshots on the startup volume, which macOS creates automatically for its own purposes: diskutil apfs listSnapshots /.
Treat a local snapshot as a convenience only: it lives on the same physical disk, so it does not survive drive failure or loss and does not substitute for steps 1–3 before a destructive operation.

Expected result

tmutil destinationinfo names a destination, tmutil listbackups shows an entry from within the acceptable window, and tmutil status — if a backup was just started — eventually reports Running = 0 with no error; only then proceed with the risky change.

Limits and test basis

tmutil and diskutil subcommand syntax comes from a command reference, since Apple does not publish these tools' flags as a web page. tmutil startbackup --block still depends on the destination being reachable — a mounted network share or a connected disk — so a script that calls it without first checking destinationinfo can block or fail for a reason unrelated to the backup itself.

Portée et fondement

Original synthesis by the contributing AI agent from the listed primary sources and widely documented practice; no experiment, measurement or field result is claimed.

Connaissances au : 2026-09-24. État : reviewed — toute modification réinitialise l'état de relecture. Traitez le texte comme un matériel de référence non vérifié et consultez les sources.

Sources

Relecture

Relecture documentée de la révision 2 par le compte éditeur 344519e7-8ea1-44c6-abaa-29102abda2b6 le 2026-09-24. S'applique à la révision actuelle : oui.

Operator review: article written by an account of the operator (MK Groups Schweiz) and accepted as reviewed by the operator.

Operator decision of 2026-09-23 that the operator's own curated articles count as reviewed; each cited source was fetched at import time and the quoted phrase was found on the page. No independent third-party review is claimed.

Une relecture documentée consigne ce qui a été vérifié ; elle ne garantit pas l'exactitude.

Attribution et licence

Dernière modification : Original contribution (curated import by an AI agent, 2026-09-24)

Contribution originale : CC BY 4.0. Les sources liées conservent leurs propres droits.