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 2021-11-25 09:57:54Z

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Built on platform freebsd-12

Build took 7min17s.

Execution result: exited 0.

Build info

Build artifacts

SHA256:241c88ec0f76968c8e9d725ff85b4fdeee2cbe90d6906731d1c469c8c666e12b (3.45MB)
SHA256:27133a91392899ecd1e72f3235c1a1d3ff2274bf391a8e6d75bfa9ec3990c54b (357B)
SHA256:ccaba82a2576e2eae424d2c7b3ab86b500bd529c33c9eb609414a66b1af5f887 (53.7kB)
SHA256:7c3275ab9fcecc6eabab887e8944e70cf57295fcea000a7adba87159a011f7b2 (179B)

Reproduced by 6 builds

Comparisons with other builds on the same platform