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Dockerfile SOURCE_DATE_EPOCH context and stage values

Introduced 2026-05-13 · score 0.94

HOW TO USE IT

When building with a remote context or a stage timestamp, define `ARG SOURCE_DATE_EPOCH=context` or `ARG SOURCE_DATE_EPOCH=<stage>` to set the build timestamp from that source. Context resolution uses the Git commit time or, for HTTP contexts, `Last-Modified` or the newest TAR entry mtime when the header is absent.

ARG SOURCE_DATE_EPOCH=context FROM alpine
ARG SOURCE_DATE_EPOCH=<stage> FROM alpine

WHY THIS HELPS

Set reproducible build timestamps from a remote context or build stage.

REQUIREMENTS AND LIMITATIONS

  • Version: dockerfile/1.24.0
  • SOURCE_DATE_EPOCH=context: Special build-arg value: resolve the main build context to a numeric Unix timestamp. Git context uses commit time; HTTP context uses `Last-Modified` or, for an archive without that header, the newest archive entry mtime.
  • SOURCE_DATE_EPOCH=<stage>: Special build-arg value that selects the timestamp associated with the named stage.
  • Prerequisite: Dockerfile frontend supports `SOURCE_DATE_EPOCH` as a special build arg since BuildKit 0.11; minimal support is available on older BuildKit with Dockerfile 1.5 frontend.
  • The context timestamp is a Git commit timestamp for Git commit builds.
  • For remote URL builds, the timestamp comes from TAR archive file metadata or the URL's `Last-Modified` header.
  • Docs conflict: Release note says remote URL timestamps may come from TAR file metadata or `Last-Modified`; versioned build-repro docs specify the newest archive entry mtime when `Last-Modified` is absent.

FIRST-PARTY EVIDENCE

Check the installed version and the source before using it. Entry JSON

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