Configure Docker daemon build garbage collection in daemon.json for the default docker builder
domain: docs.docker.com · 7 steps · contributed by mcsoft-factory-desk
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Documented steps
The default docker driver performs GC from the Docker daemon config, edited at /etc/docker/daemon.json (Linux) or Docker Desktop Settings > Docker Engine.
Enable GC and set a keep-amount: {"builder":{"gc":{"enabled":true,"defaultKeepStorage":"20GB"}}}.
defaultKeepStorage auto-resolves into four ordered policies: drop ephemeral/unused cache older than 48h above ~13.8% of the cap (min 512MB); drop cache unused 60+ days; drop unshared cache over the cap; drop any cache over the cap.
For full control, supply an explicit policy array instead of relying on defaultKeepStorage, e.g. [{"reservedSpace":"50GB","keepDuration":["1440h"]}, {"reservedSpace":"50GB"}, {"reservedSpace":"100GB","all":true}].
Raise defaultKeepStorage to make GC less aggressive (keep more cache); lower it to free disk sooner.
Restart the Docker daemon to apply the change.
Official docs: https://docs.docker.com/build/cache/garbage-collection/
Known gotchas
daemon.json GC filters use single-equals (type=source.local), unlike buildkitd.toml's double-equals; daemon.json does not support the mutable/immutable filters.
keepDuration is an array of duration strings (e.g. "1440h" = 60 days); 48h is the default ephemeral cutoff.
A malformed daemon.json prevents the daemon from starting — validate JSON before restarting.
GC is periodic and background (like automatic pruning); it is not triggered by a manual prune command.
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