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The backup verifier did not fail because the PostgreSQL dump was corrupt. It failed because each disposable restore could leave an anonymous Docker volume behind. After 34 days, 57 abandoned volumes held 156 GB, filled Docker’s separate data partition, and prevented a new PostgreSQL container from completing initdb. The immediate repair was one character: change docker rm -f to docker rm -fv. The -v tells Docker to remove anonymous volumes attached to the container, including on the forced-cleanup path.
This incident shows why successful-exit cleanup is not enough. A verifier must clean up after timeouts and kills, monitor the filesystem that actually stores Docker data, and print enough diagnostics to explain a readiness failure.
What exactly happened to the backup verifier?
A nightly check for the textstack.app project restored a fresh PostgreSQL dump into a throwaway container and ran sanity queries. The dump and storage archive completed, but the restore gate began returning the seven-word error “postgres did not become ready.” In other words, the backup artifacts had been produced; it was the disposable restore-and-check stage that failed.
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The hidden condition was storage placement. Docker’s data root was on /mnt/data, while the routine health check looked at /. The root filesystem was only 61% full, but /mnt/data had reached 100% usage with zero free bytes. Production PostgreSQL and file storage were bind-mounted on /, so live production data still had headroom; disposable restore-test data had consumed the separate Docker partition. This was a serious verification outage, but the incident report describes the leaked data as test data rather than a loss of the production database.
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| Incident measurement | Value | Qualification |
|---|---|---|
| Anonymous volumes accumulated | 57 | Collected over 34 days |
| Space attributed to the leaked volumes | 156 GB | Incident-specific measurement from Vasyl’s 2026 report |
| Root filesystem usage | 61% | The partition checked by the habitual alert |
| Docker data partition usage | 100% | /mnt/data, with zero bytes free |
| Space reclaimed during cleanup | 163 GB | Reduced /mnt/data from 100% to 17% |
The cleanup reclaimed 163 GB, a figure larger than the 156 GB attributed to the leaked volumes; those are separate measurements reported for the incident, not a general estimate of how much a volume leak consumes. The scale and duration are specific to this verifier, not an industry-wide rate.
The author summarized the design failure this way: “The backup broke the very step that verified the backup.” A separate postmortem line captures the operational risk: “a backup you never restored is a hope, not a backup.” Both are statements about this incident, not industry-wide statistics.
Why did Docker create a new volume on every run?
The official PostgreSQL image declares VOLUME /var/lib/postgresql/data. If a verification container does not provide its own mount, Docker supplies an anonymous volume for that path. Consecutive containers using that arrangement receive separate anonymous volumes, so a disposable container does not imply disposable data.
Anonymous does not mean temporary. Docker’s documented behavior is that anonymous volumes persist after ordinary container removal unless the container is run with --rm or the volume is explicitly removed. A successful verifier run used --rm, so Docker normally deleted the anonymous volume when the process exited.
The leak appeared on abnormal exits. A timeout or kill could prevent the normal --rm cleanup from running. The timeout handler then called docker rm -f, which removed the container but left its anonymous PostgreSQL volume. One initialized pgdata volume per failed run accumulated for 34 days. Because each failure left storage behind, the behavior could remain invisible while the verifier was healthy and then become more damaging precisely when it began having trouble.
This is why “we use --rm” is not a complete cleanup policy. It describes the automatic cleanup associated with a container’s exit; it does not replace a correct explicit-removal path for timeouts, forced kills, or any other route that removes the container before that normal cleanup can finish.
Does docker rm -f delete volumes?
No. docker rm -f force-removes the container, but it does not remove its anonymous volumes. Add -v to remove anonymous volumes associated with that container.
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| Command | Container | Anonymous volumes | Named volumes |
|---|---|---|---|
docker rm |
Removes a stopped container | Retained | Retained |
docker rm -f |
Force-removes a running or stopped container | Retained | Retained |
docker rm -fv |
Force-removes the container | Removed when associated with it | Retained |
docker run --rm |
Removes the container automatically at exit | Removed on the normal exit cleanup path | Not deleted by that automatic cleanup |
That distinction is why the repair was a one-letter change:
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docker rm -fbecame:
docker rm -fvThe Docker CLI’s -v (also written --volumes) removes anonymous volumes associated with the removed container. It does not erase named volumes, which are treated as explicitly managed state. The flag addresses the specific container-removal path; it is not a substitute for deciding what to do with volumes that have already become orphaned.
Why did PostgreSQL readiness fail after the disk filled?
When /mnt/data reached 100%, a fresh throwaway PostgreSQL container could not initialize its data directory. PostgreSQL’s initdb therefore failed before the server could become ready, producing a readiness error rather than a useful storage diagnosis. A message saying only that PostgreSQL did not become ready can sound like a database or dump problem, even when the immediate blocker is that Docker’s storage filesystem has no free space.
The failure created a closed loop:
- The verifier started a new PostgreSQL container.
- Docker allocated another anonymous volume under its data root.
- The full partition prevented successful initialization.
- The readiness check failed.
- The timeout cleanup used
docker rm -f, leaving the new anonymous volume behind. - The next run had even less room.
The verifier therefore consumed the storage pool it depended on to test restores. It is a useful distinction when diagnosing an incident: the report says the dump and storage tarball succeeded, but the restore gate failed after Docker could no longer initialize PostgreSQL’s data directory. That evidence points to a failure in the verification environment, not by itself to a corrupt backup.
A readiness message alone concealed the cause. The verifier needed to report container logs, filesystem usage, and Docker’s own storage accounting at the point of failure.
How do you repair leaked volumes safely?
First stop creating new test containers, then remove the failed verifier containers with the volume flag and prune only the disposable orphan volumes covered by your policy. The order matters: changing the cleanup behavior prevents a continuing leak, while cleanup of existing leftovers recovers the space already consumed.
1. Fix the trap and timeout path
Put the same volume-aware removal in the cleanup trap and in the code that reaps containers after a timeout:
cleanup() {
docker rm -fv "$VERIFY_CONTAINER" >/dev/null 2>&1 || true
}
trap cleanup EXIT INT TERMUse the real container identifier rather than relying on a name that may not exist after a partial startup. Keep the error path tolerant of an already-removed container, but do not silently omit the -v. The important property is consistency: every path that removes the verifier container must also remove its associated anonymous data volume.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware match2. Reap containers left by earlier runs
Apply docker rm -fv to the known leaked verification containers. Removing only the containers is insufficient because their anonymous PostgreSQL volumes are the storage that accumulated. The incident fix included both a change to the trap and a reap of leaked verify containers from earlier runs.
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3. Prune orphaned anonymous volumes deliberately
The incident cleanup also added:
docker volume prune -fUse this only when your environment has a clear orphan-volume policy. A prune command removes unused volumes; it is a broad cleanup action, not a targeted replacement for cleaning up the verifier’s own container. If another workflow depends on an unused volume being retained, an indiscriminate prune can remove state you meant to keep. Distinguish disposable verification volumes from retained state before automating a prune, and do not assume that a volume is disposable merely because no container currently uses it.
4. Add diagnostics to the readiness failure
On startup or readiness failure, emit the PostgreSQL container logs, the filesystem containing Docker’s data root, and Docker’s storage summary:
docker logs "$VERIFY_CONTAINER"
df -h /mnt/data
docker system dfThese outputs turn “postgres did not become ready” into evidence showing whether initialization failed, the Docker partition is full, or old artifacts are consuming the pool. Use the actual data-root mount in place of /mnt/data if your deployment stores Docker data elsewhere. A root-only check is not a substitute: it can report ample space while the filesystem Docker needs is exhausted.
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Monitor the mount that contains Docker’s data root, not just the host’s root mount. In this incident, df -h / reported a comfortable 61% while Docker’s storage partition was exhausted.
- Identify where Docker stores container and volume data in your deployment.
- Alert on that mount’s free space and use the same path in normal health checks and failure diagnostics.
- Include Docker’s storage accounting so volume, image, and container usage can be considered alongside filesystem capacity.
- Set a headroom threshold that stops new verification jobs before initialization becomes impossible.
The practical troubleshooting question is not simply “Is the server disk full?” but “Is the filesystem holding Docker’s data full?” The root mount and Docker’s data mount can have different capacity and different workloads. Checking only the familiar root mount can leave the team looking in the wrong place while new verification attempts fail.
A verifier shares the storage pool with the Docker engine that runs it. If test artifacts can consume that pool without a quota or alert, the verification system can disable itself while trying to prove that backups work. This incident’s 57 leaked volumes accumulated over 34 days; it does not establish how quickly another system will fill, since dump sizes and available storage vary.
Which storage design prevents a repeat?
No single design is best for every restore test. Compare designs by whether cleanup still works on forced exits, whether data can become orphaned, whether named state must be reset between runs, capacity constraints, prune-command blast radius, and the quality of diagnostics when PostgreSQL fails to become ready.
| Design | Cleanup on forced exit | Orphan risk | Reset requirement | Main constraint | Diagnostic and operational notes |
|---|---|---|---|---|---|
Anonymous volume plus docker rm -fv |
Handled when every removal path uses -v |
Possible if a path bypasses the trap | None; each run starts with a new volume | Consumes Docker’s data partition | Simple isolation; requires monitoring and robust traps |
| Named volume reused between runs | Not automatic; lifecycle is explicit | Lower accidental-orphan risk, but stale state can persist | Yes; empty it before initdb |
Operator must safely reset retained state | Can make storage ownership obvious; prune must not remove it |
| Temporary filesystem | Data disappears with the container | Structurally low | None after teardown | Capacity is constrained by available memory and must cover the dump | Evaluate dump size before adoption |
Anonymous volumes: simplest isolation
Give each restore a fresh data directory and make forced cleanup equivalent to normal cleanup. This is the closest match to the existing verifier, provided the trap, timeout handler, and manual reaper all use docker rm -fv. Its weakness is operational rather than mysterious: a missed exceptional path can leave another anonymous volume, so cleanup and filesystem monitoring must be treated as part of the design.
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A named volume mounted at /var/lib/postgresql/data can make ownership and retention clearer. It must be emptied before a new initdb, and the automation must define who resets it, when that reset happens, and how accidental deletion is prevented. Reusing the same named volume is not a “set it and forget it” alternative: stale database files are still present until deliberately cleared, and Docker’s rm -v does not delete named volumes.
Temporary filesystem: automatic disappearance with a memory trade-off
A temporary filesystem can make test data vanish with the container, but its usable capacity is tied to available memory. Compare the dump size with the memory-backed space available, allowing for the restore’s needs, before adopting it. It may reduce the risk of persistent orphaned disk data, but it does not remove the need to ensure the chosen capacity can accommodate the test.
What should the cleanup workflow look like?
- Create the container with an identifiable name or ID. Record that identifier so the timeout and cleanup paths can target the intended verifier container.
- Install cleanup immediately. The trap must run on normal exit and interruption, while timeout handling must also remove volumes explicitly.
- Use
docker rm -fveverywhere the verifier removes its container. Do not reserve the volume flag for the happy path. - Capture failure evidence before teardown when possible. Save
docker logs,df -hfor Docker’s data mount, anddocker system df. - Check capacity before another restore. If Docker’s filesystem is full, diagnose and clear the intended disposable artifacts rather than repeatedly starting containers that cannot initialize.
- Reap leftovers on the next run. A startup sweep can remove known disposable verifier containers and their anonymous volumes.
- Run pruning under an explicit policy. Keep retained named volumes outside the disposable set and document what automation is allowed to delete.
- Alert on the correct storage pool. Watch the Docker data filesystem as well as the host root, so an unrelated healthy mount does not mask the problem.
This workflow keeps the two kinds of cleanup separate. Container removal with -v handles the anonymous volume attached to the container being removed; a prune is for orphaned volumes and needs an explicit policy. Neither action replaces the other, and neither makes the Docker data filesystem irrelevant to monitor.
What failure modes still need testing?
A cleanup design is not proven by a successful run. Exercise the paths that previously bypassed --rm:
- Terminate the verifier while PostgreSQL is initializing.
- Force a timeout during a long restore.
- Kill the wrapper process before it reaches its normal exit handler.
- Make PostgreSQL fail readiness and confirm that logs and storage diagnostics are emitted.
- Restart the host or Docker engine during verification, then confirm the next run reaps the abandoned container and volume.
- Verify that the cleanup does not remove named volumes intended to be retained.
After each scenario, check that no disposable volume remains and that the diagnostic output identifies the relevant mount and container. In particular, test both halves of the failure: whether the old container and volume are cleaned up, and whether a subsequent run reports useful evidence if PostgreSQL still cannot become ready.
What is the practical lesson for backup verification?
Restore testing is part of the backup, not an optional report generated after it. A verifier that leaves data behind on every exceptional exit can exhaust its own execution environment and turn a storage problem into a false conclusion about backup integrity. In this incident, the dump and archive succeeded, but the restore check could not proceed once Docker’s separate data partition filled.
The reliable pattern is straightforward: make cleanup idempotent and volume-aware, observe Docker’s actual data filesystem, and make readiness failures self-diagnosing. The one-letter fix solved the immediate leak; the guardrails prevent the same failure loop from returning.
Frequently Asked Questions
Can a named PostgreSQL volume be removed by docker rm -fv?
No. The -v option removes anonymous volumes associated with the container, while named volumes are retained. A named-volume design therefore requires a separate, deliberate reset and retention policy.
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Why did the normal --rm option not protect this verifier?
--rm handles the container’s normal exit cleanup. A timeout, kill, or interrupted wrapper can bypass that path, so the exceptional removal handler must explicitly include -v.
Why can df -h / show space when Docker cannot start PostgreSQL?
The filesystem checked by df -h / may not be the one holding Docker’s data root. In the textstack.app incident, / was 61% used while Docker’s /mnt/data partition was at 100% with zero free bytes.
Is a temporary filesystem always safer for disposable restores?
It reduces orphaned-disk data because the contents disappear with the container, but its capacity is limited by available memory. Compare the dump size and the available memory-backed capacity before choosing it.
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What should an alert include when PostgreSQL never becomes ready?
Include the container logs, usage for the filesystem holding Docker’s data root, and docker system df output. Those details help distinguish initialization errors from an exhausted Docker storage pool.
Will docker volume prune -f only remove this verifier’s volumes?
Do not assume that. The incident used pruning for orphaned anonymous volumes, but prune should run only under a policy that distinguishes disposable verification volumes from state you intend to retain.
How much space did the fix recover in the reported incident?
Vasyl’s 2026 incident report says cleanup reclaimed 163 GB and reduced /mnt/data from 100% usage to 17%. The 156 GB and 163 GB figures are incident-specific measurements, not general expectations.
The Bottom Line
Bottom line: docker rm -f can remove a failed container while leaving its anonymous PostgreSQL volume behind. Use docker rm -fv on every forced-cleanup path, deliberately handle existing orphans, and monitor the filesystem that actually contains Docker’s data root. A readiness error is much easier to solve when it includes container logs and Docker storage usage.
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