Job orb


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orb: check opam package reproducibility

This tool can check if an opam package build is reproductible (cf. It has two subcommands: build and rebuild.

The orb build conducts a build of an opam package, and collects the build result (and hashes thereof) and the build input (or build info), consisting of:

The orb rebuild takes this data as input and conducts a second build with the same environment, and compares that the hashes of the produced binaries are identical.

The orb build also has a command-line flag "--twice" to conduct a build and a rebuild directly afterwards. For debugging reproducibility, a "--keep-build" (useful with opam's "--keep-build-dir") option is provided that allows to compare intermediate build products as well.

Please have a look at "--diffoscope", "--out", "--switch-name", "--solver-timeout", "--date", and other command line parameters.

It is currently used as a payload of builder-worker to run the reproducible MirageOS unikernels infrastructure.

Binary packages for different platforms (Debian, Ubuntu, FreeBSD) are available at

Install & use

$ opam pin git+
$ orb build --twice --repos=default: cmdliner

Simple (and fast) failing and successful reproducible opam packages are in the reproducible-testing-repo.

Build 2022-01-14 11:43:28Z

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Built on platform freebsd-12

Build took 5min23s.

Execution result: exited 0.

Build info

Build artifacts

SHA256:7f3d0decf9bd51c07f37a97ba8579bf21711c3a24749162d29c9250d395ce0e6 (3.45MB)
SHA256:27133a91392899ecd1e72f3235c1a1d3ff2274bf391a8e6d75bfa9ec3990c54b (357B)
SHA256:f0bae5ae93f8f1a7241589b7a848a27c0dd159ef8632580102ac631ab644c805 (53.7kB)
SHA256:807822222231e96a09553362d8cc20d7573478d9e73ddf7aeebb6f8d2991e7de (179B)

Reproduced by 12 builds

Comparisons with other builds on the same platform