Docker: No Space Left on Device

Your build stops dead:

write /var/lib/docker/...: no space left on device

Nine times out of ten your disk isn't actually full of your files — it's full of Docker's leftovers. Every image layer, stopped container, and unused volume you've ever created is sitting in /var/lib/docker until you clean it up.

Step 1: See what Docker is holding

Before deleting anything, look at where the space went:

docker system df        # summary: images, containers, volumes, build cache
df -h /var/lib/docker   # confirm the underlying filesystem is the full one

docker system df breaks it down by type and shows a RECLAIMABLE column — that's your target.

Step 2: Prune the safe stuff first

Start with dangling images and stopped containers — nothing you're using loses data:

docker container prune   # remove stopped containers
docker image prune       # remove dangling (untagged) images

Step 3: The bigger sweep

If you need more room, prune everything unused in one shot:

docker system prune -a    # removes ALL images not used by a running container

-a is aggressive: it deletes every image without a running container, so the next build re-pulls base images. Great for reclaiming gigabytes, but expect the next build to be slower.

Watch out: volumes hold your data

docker system prune -a does not touch named volumes by default — that's deliberate, because volumes usually hold databases. Only add --volumes if you're certain nothing important lives there:

docker volume ls                 # look before you leap
docker volume prune              # removes volumes not attached to any container

Build cache is often the real hog

On machines that build a lot, the BuildKit cache balloons:

docker builder prune             # clear build cache specifically

The checklist

1. docker system df — find the reclaimable space.
2. docker container prune + docker image prune — safe wins first.
3. docker system prune -a — bigger sweep (re-pulls later).
4. docker builder prune — if build cache is the culprit.
5. Only touch docker volume prune after checking docker volume ls.