After
rebuilding all added/modified packages in Trisquel, I have been circling around the elephant in the room: 99% of the binary packages in Trisquel comes from Ubuntu, which to a large extent are built from Debian source packages. Is it possible to rebuild the official binary packages identically? Does anyone make an effort to do so? Does anyone care about going through the differences between the official package and a rebuilt version?
Reproducible-build.org s effort to track
reproducibility bugs in Debian (and other systems) is amazing. However as far as I know, they do not confirm or deny that their rebuilds match the official packages. In fact, typically their rebuilds do not match the official packages, even when they say the package is reproducible, which had me surprised at first. To understand why that happens, compare the
buildinfo file for the official coreutils 9.1-1 from Debian bookworm with the
buildinfo file for reproducible-build.org s build and you will see that the SHA256 checksum does not match, but still they declare it as a reproducible package. As far as I can tell of the situation, the purpose of their rebuilds are not to say anything about the official binary build, instead the purpose is to offer a QA service to maintainers by performing two builds of a package and declaring success if both builds match.
I have felt that something is lacking, and months have passed and I haven t found any project that address the problem I am interested in. During my earlier work I created a project called
debdistreproduce which performs rebuilds of the difference between two distributions in a GitLab pipeline, and display
diffoscope output for further analysis. A couple of days ago I had the idea of rewriting it to perform rebuilds of a single distribution. A new project
debdistrebuild was born and today I m happy to bless it as
version 1.0 and to announces the project! Debdistrebuild has rebuilt the top-50 popcon packages from Debian bullseye, bookworm and trixie, on amd64 and arm64, as well as Ubuntu jammy and noble on amd64, see the
summary status page for links. This is intended as a proof of concept, to allow people experiment with the concept of doing GitLab-based package rebuilds and analysis. Compare how
Guix has the
guix challenge command.
Or I should say
debdistrebuild has
attempted to rebuild those distributions. The number of identically built packages are fairly low, so I didn t want to waste resources building the rest of the archive until I understand if the differences are due to consequences of my build environment (plain
apt-get build-dep followed by
dpkg-buildpackage in a fresh container), or due to some real difference. Summarizing the results,
debdistrebuild is able to rebuild 34% of Debian bullseye on amd64, 36% of bookworm on amd64, 32% of bookworm on arm64. The results for trixie and Ubuntu are disappointing, below 10%.
So what causes my rebuilds to be different from the official rebuilds? Some are trivial like the classical problem of
varying build paths, resulting in a different
NT_GNU_BUILD_ID causing a mismatch. Some are a bit strange, like a
subtle difference in one of perl s headers file. Some are due to
embedded version numbers from a build dependency. Several of the build logs and diffoscope outputs doesn t make sense, likely due to bugs in my build scripts, especially for Ubuntu which appears to strip translations and do other build variations that I don t do. In general, the classes of reproducibility problems are the expected. Some are
assembler differences for GnuPG s gpgv-static, likely triggered by upload of a new version of gcc after the original package was built. There are at least two ways to resolve that problem: either use the same version of build dependencies that were used to produce the original build, or demand that all packages that are affected by a change in another package are rebuilt centrally until there are no more differences.
The current design of
debdistrebuild uses the latest version of a build dependency that is available in the distribution. We call this a idempotent rebuild . This is usually not how the binary packages were built originally, they are often built against earlier versions of their build dependency. That is the situation for most binary distributions.
Instead of using the latest build dependency version, higher reproducability may be achieved by rebuilding using the same version of the build dependencies that were used during the original build. This requires parsing
buildinfo files to find the right version of the build dependency to install. We believe doing so will lead to a higher number of reproducibly built packages. However it begs the question: can we rebuild that earlier version of the build dependency? This circles back to really old versions and
bootstrappable builds eventually.
While rebuilding old versions would be interesting on its own, we believe that is less helpful for trusting the latest version and improving a binary distribution: it is challenging to publish a new version of some old package that would fix a reproducibility bug in another package when used as a build dependency, and then rebuild the later packages with the modified earlier version. Those earlier packages were already published, and are part of history. It may be that ultimately it will no longer be possible to rebuild some package, because proper source code is missing (for packages using build dependencies that were never part of a release); hardware to build a package could be missing; or that the source code is no longer publicly distributable.
I argue that getting to 100% idempotent rebuilds is an interesting goal on its own, and to reach it we need to start measure idempotent rebuild status.
One could conceivable imagine a way to rebuild modified versions of earlier packages, and then rebuild later packages using the modified earlier packages as build dependencies, for the purpose of achieving higher level of reproducible rebuilds of the last version, and to reach for bootstrappability. However, it may be still be that this is insufficient to achieve idempotent rebuilds of the last versions. Idempotent rebuilds are different from a reproducible build (where we try to reproduce the build using the same inputs), and also to bootstrappable builds (in which all binaries are ultimately built from source code). Consider a cycle where package X influence the content of package Y, which in turn influence the content of package X. These cycles may involve several packages, and it is conceivable that a cycle could be circular and infinite. It may be difficult to identify these chains, and even more difficult to break them up, but this effort help identify where to start looking for them. Rebuilding packages using the same build dependency versions as were used during the original build, or rebuilding packages using a bootsrappable build process, both seem orthogonal to the idempotent rebuild problem.
Our notion of rebuildability appears thus to be complementary to
reproducible-builds.org s definition and
bootstrappable.org s definition. Each to their own devices, and Happy Hacking!
Addendum about terminology: With idempotent rebuild I am talking about a rebuild of the entire operating system, applied to itself. Compare how you build the latest version of the
GNU C Compiler: it first builds itself using whatever system compiler is available (often an earlier version of gcc) which we call step 1. Then step 2 is to build a copy of itself using the compiler built in step 1. The final step 3 is to build another copy of itself using the compiler from step 2. Debian, Ubuntu etc are at step 1 in this process right now. The output of step 2 and step 3 ought to be bit-by-bit identical, or something is wrong. The comparison between step 2 and 3 is what I refer to with an idempotent rebuild. Of course, most packages aren t a compiler that can compile itself. However entire operating systems such as Trisquel, PureOS, Ubuntu or Debian are (hopefully) a self-contained system that ought to be able to rebuild itself to an identical copy. Or something is amiss. The reproducible build and bootstrappable build projects are about improve the quality of step 1. The property I am interested is the identical rebuild and comparison in step 2 and 3. I feel the word idempotent describes the property I m interested in well, but I realize there may be better ways to describe this. Ideas welcome!
Twenty years ago, it was easy to dislike Microsoft. It was the quintessential evil MegaCorp that was quick to squash competition, often ruthlessly, but in some cases slowly through a more insidious process of embracing, extending, and exterminating anything that got in the way. This was the signature personality of Ballmer-era Microsoft that also inspired and united the software freedom fighting forces that came together to safeguard things that mattered to them and were at risk.I remember the era when the Novell, SCO, and Microsoft saga cast fear, uncertainty, and doubt on the future of open Unix and Linux and on what would happen to the operating systems that we loved if the suits of Redmond prevailed. Looking back, I&aposm glad that the arc of this story has bent towards justice, and I shudder at the possibilities had it worked out differently.Looking at today&aposs Microsoft, I&aposm amazed at how much change a leader with the right vision can make to the trajectory of a company that even makes an old-school software freedom advocate as me admire and even applaud the strides it has taken in the last 10 or so years that has dramatically shifted the perception of Microsoft. The personality of the Satya-era Microsoft is one to behold. While it will take more time to win back the trust, we see the tides changing and the positivity is important for the entire industry.For Microsoft, it was TypeScript and VS Code that helped change the narrative internally which led to its internal resurgence and acceptance of open source. Its acquisition of GitHub propelled it forward within the community overnight. Its contributions to the Linux kernel and other major software projects have also been consequential in changing its public perceptions.It takes a while to claw back trust and is very easy to breach. This time, however, Microsoft seems to understand this dynamic more than it did 20 years ago. All it took was the right leadership.
Like each month, have a look at the work funded by 
Dear Debian community,
Statement on Daniel Pocock
The Debian project has successfully taken action to secure its
trademarks and interests worldwide, as detailed in our press