---
layout: event_detail
title: .buildinfo files
event: berlin2016
order: 90
permalink: /events/berlin2016/buildinfofiles/
---

## Early work

A goal was to minimise the conditions needed to reproduce a binary.

`.buildinfo` files ("buildinfo files") would be a formula to reproduce a build.  It should be small as possible.

They don't/can't describe every possible input;
[a] build process [can be] affected by obscure things or external, variable factors.

1. buildinfo files:
record inputs to the build that produced the output, so that you can recreate its state.

2. analysis of buildinfo and outputs:
as more builders provide buildinfo files, we can look for intersections (reproducible binaries), and causes of any differences (non-reproducibility)

3. the ideal (reproducible) build would depend only the source code and build dependencies

buildinfo files should:

 - contain the minimal information needed to produce a given binary
 - be small, compact, and easily distributable


## buildinfo files might contain:

- source package (name, version, hash?)
- binaries produced (name, arch, checksums)
- build dependencies (recursively)
- build path (until recently?)
- environment variables (since recently?)

In Debian, buildinfo is a separate file.

In Arch Linux, buildinfo is included in the package files (but signatures are detached).


## Consuming and aggregating buildinfo files:

in Debian, buildinfo files are used when:

  * DD uploads a package
  * debian-ftp system distributes packages
  * end-user installs packages

and now we also realised:

  * rebuilders
  * buildinfo distributors


## Further work

We want to collate and distribute buildinfo files from external parties too;
not just those from Debian developers and the official builds.

Collecting and distributing those, is a quite different task than just distributing buildinfo from Debian's official builds.

[buildinfo.debian.net](https://buildinfo.debian.net) already collects and distributes some non-official buildinfo files.

We will need to write tools making it easy to test [reproducibility] and submit buildinfo,
and tools to retrieve buildinfo files/signatures when installing.

Signed buildinfos save people from having to build every package themselves:
it gives them sufficient confidence to trust pre-built binaries.


## Ongoing concerns

buildinfo files should to be detailed enough to explain the causes of non-reproducibility;
but too much information ($HOME, hostname, installed packaged versions)

An argument arose that a normalised build environment avoids lots of reproducibility issues,
like build path, environment, etc., affecting the build.
Whilst that would be easier, some of us think that is really a bug in the software that ought to be fixed.

In the extreme case, 
when a build-dependency affects an output binary,
we may need to generate a new set of buildinfo files
describing that situation.