Disk space

Docker cleanup has two separate steps:

1. Remove unused Docker data.
2. Return the freed space to the host filesystem.

Removing images and build cache does not necessarily reduce the size of Docker's underlying virtual disk immediately.

Remove unused Docker data

Run these commands wherever the Docker daemon is running:

docker image prune -a -f
docker builder prune -a -f
docker system df

The final command shows Docker's remaining disk usage. Confirm that the build cache and other reclaimable data are close to zero.

These commands are safe to repeat, but docker image prune -a removes every image not currently used by a container. The images will need to be downloaded or rebuilt again when next used.

For a more aggressive cleanup that also removes stopped containers, unused networks, and unused volumes:

docker system prune -a --volumes -f
docker system df

Only include --volumes when unused Docker volumes do not contain data you need.

Docker inside Composery

Composery ships its own Docker daemon, and it is the largest thing that will grow your /data volume. Its storage deliberately lives there rather than on the container's root filesystem: /etc/docker/daemon.json sets data-root to /data/docker, and /etc/containerd/config.toml sets containerd's root to /data/containerd. Since Docker Engine 29 the containerd store holds the image layers and container snapshots, so both settings are needed - data-root alone would move volumes and daemon state while every layer stayed on the root filesystem. See Persistence.

The practical consequence: images you pull inside Composery consume the volume you sized, not the image. On a small instance a few large images are the whole disk. Prune from a terminal inside Composery, which is where that daemon runs:

docker system df
docker image prune -a -f
docker builder prune -a -f

df -h /data shows what is left. This is separate from the host-level cleanup below, which reclaims space from the Docker that runs Composery itself.

Linux

On native Linux, Docker normally stores its data directly on the host filesystem. Once unused Docker data is removed, the freed space should become available to the host automatically.

Check Docker's storage location and available disk space:

docker info --format '{{.DockerRootDir}}'
df -h

The default Docker root is usually /var/lib/docker.

When Docker runs inside a VM, WSL, Lima, Colima, or another virtualized environment, the virtual disk may need to be compacted separately using that environment's tooling.

Windows with Docker Desktop

Docker Desktop stores Linux container data in a dynamically growing VHDX file. Deleting Docker data frees space inside the virtual disk, but does not automatically reduce the VHDX file's size on Windows.

When the configured scheduled task is available, run:

Start-ScheduledTask -TaskName "Docker VHDX compact"
Get-Content "$env:USERPROFILE\.docker\compact-docker-vhdx.log" -Tail 20 -Wait

The task runs elevated, so it should not require a new UAC prompt.

Manual compaction

Quit Docker Desktop, open PowerShell as Administrator, and run:

wsl --shutdown

Optimize-VHD `
  -Path "$env:LOCALAPPDATA\Docker\wsl\disk\docker_data.vhdx" `
  -Mode Full

The exact VHDX path depends on the Docker Desktop version and installation. Check Docker Desktop's disk image location before running Optimize-VHD.

wsl --shutdown stops Docker Desktop and every running WSL distribution, including Ubuntu. Unsaved processes inside those distributions will be terminated.

In one previous cleanup, compaction reduced the Docker virtual disk from 498.7 GB to 59.4 GB. The result depends on how much unused space exists inside the disk.

macOS with Docker Desktop

Docker Desktop also stores container data inside a Linux virtual disk on macOS. After pruning Docker data, use Docker Desktop's storage controls to reclaim or resize the disk image:

Docker Desktop → Settings → Resources → Advanced

The available controls and labels vary by Docker Desktop version. Resetting Docker Desktop will reclaim space, but also removes local containers, images, volumes, and other Docker data.