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Docker and disk space

diskdiet clean asks Docker to remove:

  • stopped containers created more than --older-than ago,
  • images no container uses, created more than --older-than ago,
  • build cache not used for --older-than,
  • with --volumes only: every volume no container uses. Volumes have no age filter and can hold databases, so diskdiet never removes them unless you ask.

These are Docker's own container prune, image prune --all, builder prune --all and volume prune --all commands with an until filter, run against your current docker context (Docker Desktop, OrbStack, Colima, Rancher Desktop or Docker Engine).

Note that Docker's age filter for images is the image's creation time, which is when it was built rather than when you pulled it. An image you pulled today can be older than 30 days, and if no container uses it, it counts as old.

Docker Desktop's disk file

On macOS and Windows, Docker Desktop keeps everything in a virtual disk file. After pruning, the space is free inside that disk, but the file may not shrink right away.

macOS: Docker Desktop hands freed space back to macOS by itself, which can take a few minutes. To cap the disk's size, open Docker Desktop → Settings → Resources → Advanced → Virtual disk limit.

Windows (WSL 2): the disk file (for example %LOCALAPPDATA%\Docker\wsl\disk\docker_data.vhdx; older versions use ...\wsl\data\ext4.vhdx) does not shrink by itself. To compact it:

  1. Quit Docker Desktop, then run wsl --shutdown.
  2. Compact the file, either:
  3. on Windows Pro or Enterprise, in an administrator PowerShell: Optimize-VHD -Path "<path to the .vhdx>" -Mode Full
  4. on any edition, in an administrator prompt: 
    diskpart
select vdisk file="<path to the .vhdx>"
attach vdisk readonly
compact vdisk
detach vdisk
exit
  5. Start Docker Desktop again.