Docker /dev/shm No Space Left On Device
A container can fail with write /dev/shm/...: no space left on device while the host disk still has plenty of free space. Treat it as a shared-memory, session, or health-check loop incident before deleting app data or Docker volumes.
Find the biggest storage culprit first.
Run the Chrome or Edge web scan, delete one approved low-risk item free, then use the $29 Deep Cleanup only if meaningful space remains.
Separate host disk, container shared memory, and runaway sessions.
These checks are read-only. They show whether the failure is ordinary disk pressure, a tiny default 64 MB /dev/shm, or a request loop creating too many session artifacts.
container="YOUR_CONTAINER_NAME"
echo "== host and container filesystems =="
df -h /
docker exec "$container" sh -lc 'df -h / /tmp /dev/shm 2>/dev/null || true'
docker exec "$container" sh -lc 'df -i / /tmp /dev/shm 2>/dev/null || true'
echo "== largest /dev/shm entries =="
docker exec "$container" sh -lc 'find /dev/shm -maxdepth 2 -type f -printf "%s %p\n" 2>/dev/null | sort -nr | head -40'
echo "== recent shared-memory/session errors =="
docker logs --since=2h "$container" 2>&1 | grep -Ei "dev/shm|no space left|SIGBUS|session|health" | tail -80What Not To Delete First
- Do not prune Docker volumes because
/dev/shmis full. Volumes may contain databases or app state and may not be related. - Do not delete random session files while active workers are still writing. Stop the loop or route first, then clean stale files.
- Do not only increase
shm_sizeif a health check or redirect loop is creating a new session every second. - Do not treat
SIGBUSworkers as a normal app crash until shared-memory pressure is measured.
Common Root Causes
- Docker's default container
/dev/shmis too small for the workload. - A reverse proxy or health check hits an authenticated route and creates session files repeatedly.
- Browser automation, databases, Python workers, or image tooling use shared memory for temporary state.
- Workers crash and restart while leaving stale shared-memory files behind.
- The app logs the symptom as HTTP 400 or worker
SIGBUS, hiding the storage boundary.
Use this when maintainers ask for useful logs.
This keeps the thread focused on evidence they can act on without exposing secrets or deleting data.
I would capture this as a /dev/shm pressure incident, not ordinary host disk-full yet.
Useful evidence:
- container `df -h /dev/shm /tmp /` and `df -i /dev/shm /tmp /`
- largest files under `/dev/shm`, grouped by prefix such as session IDs
- request logs around the growth window, especially health checks, redirects, and unauthenticated paths
- worker restart logs showing SIGBUS or "no space left on device"
- compose/run config showing `shm_size` or Docker's default 64 MB shared memory
Acceptance check for a fix:
- the health-check route no longer creates sessions
- `/dev/shm` usage stabilizes over the previous failure window
- stale session cleanup only runs after active writers are stopped or aged out
- alerting watches `/dev/shm` free bytes separately from host disk free bytesStill not sure what is safe?
Use the free browser cleanup for local Mac storage, or request the $29 Deep Cleanup when the evidence points to a Docker, session, or shared-memory cleanup boundary.
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