Docker Error: No Space Left on Device

Docker has run out of disk space — usually from accumulated unused images, stopped containers, and build cache, not the disk itself being full.

What This Error Means

This means Docker's storage area (images, containers, volumes, build cache — typically under /var/lib/docker on Linux) has consumed all available disk space, or the specific filesystem/partition Docker uses is full.

Why It Occurs

Docker accumulates unused images, stopped containers, dangling build layers, and unused volumes over time unless actively cleaned up — this is extremely common on development machines and CI runners that build images frequently without pruning.

Symptoms

⚠ Builds fail partway through with this error
⚠ Containers fail to start or write to disk
⚠ General disk-full symptoms elsewhere on the system too, if Docker shares the same partition

Common Causes

• Accumulated unused/dangling images from repeated builds
• Stopped containers never removed
• Unused volumes accumulating data
• Build cache growing unbounded over many builds

How to Fix It

Check what Docker is actually using: `docker system df` — shows a breakdown of images, containers, volumes, and build cache size
Remove unused data safely: `docker system prune` (removes stopped containers, unused networks, dangling images, and build cache — NOT volumes or running containers)
For a more aggressive cleanup including unused (not just dangling) images: `docker system prune -a`
To also remove unused volumes (check first — this can delete data you need): `docker system prune -a --volumes`
Check overall disk usage on the host to confirm the fix actually freed meaningful space: `df -h`

Command	Purpose
docker system df	See a breakdown of what's consuming Docker's disk space
docker system prune	Remove unused containers, networks, dangling images, and build cache (safe default)
docker system prune -a --volumes	Aggressive cleanup including unused images and volumes — verify you don't need any of it first

Verification

✓ `df -h` shows meaningfully more free space after cleanup
✓ A previously-failing build now completes successfully

Prevention

→ Schedule regular `docker system prune` runs (e.g. a weekly cron job) on development machines and CI runners
→ Use multi-stage Docker builds to reduce final image size and intermediate layer accumulation