agent failed to detect that Duplicacy was backing up an empty directory after a mount failed silently

TL;DR

An empty backup that succeeds is a failure wearing a success costume: when the source mount failed, duplicacy backed up the empty mount point and reported a clean run. Add a sanity gate to the job's verification: compare the snapshot's file count and total size against the source's expected ranges and the previous snapshot, and alert when a snapshot's contents collapse toward zero, whatever the job's exit status says.

agent failed to detect that Duplicacy was backing up an empty directory after a mount failed silently

Use this when

• The job or restore fails with this symptom: agent failed to detect that Duplicacy was backing up an empty directory after a mount failed silently.
• You are working on an agent verifying Duplicacy backups of mounted filesystems and the failure repeats on the same target or schedule.
• You need the failing job, stage, or component isolated before changing retention or infrastructure.

Not for this skill when

• A legitimately near-empty source, such as a new share, where the gate needs an expectation set by the owner rather than history.
• The error text names a different product, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Inspect the suspect snapshot's contents and file count against the snapshots before it. Verify: the collapse is quantified
2. Check the source mount's state at backup time from system logs and confirm the empty-directory mechanism. Verify: the cause is proven
3. Add the content gate: file count and size deltas beyond a threshold fail verification and alert. Verify: empty backups now fail loudly
4. Re-run the backup with the mount healthy and confirm the new snapshot's contents match the source. Verify: a real backup replaces the hollow ones
5. Audit past snapshots for the same collapse signature across other mounted sources. Verify: the pattern is checked fleet-wide

Variant phrasings

agent missed duplicacy backing up empty directory mount failed

The verbatim phrasing.

duplicacy empty backup silent mount failure content check agent

The content-check phrasing.

agent backup succeeded empty snapshot file count gate fix

The gate phrasing.

Compatibility: Agent detection of silent backup source failures for Duplicacy jobs

Why it happens

Backup tools faithfully copy what the filesystem shows them, and a failed mount shows an empty directory that is a perfectly valid thing to copy. Exit status cannot see the difference between an empty source and an emptied one; only content expectations can.

Edge cases / pitfalls

• Mount checks belong before the backup too; a pre-flight that the mount shows expected top-level entries prevents the hollow run entirely.
• Thresholds should use both absolute floors and relative drops; a growing source makes pure relative checks drift.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_qR0kbpRJH31qFDtGB6LHbw