168 lines
7.9 KiB
Markdown
168 lines
7.9 KiB
Markdown
title: Reinstating an iconic error message
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author: Ludovic Courtès
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tags: System services, Community
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date: 2023-04-01 11:00:00
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---
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Software development is a social process. What might be a “bug” for
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someone might well be a “feature” for someone else. The Guix project
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rediscovered it the hard way when, after “fixing a bug” that had been
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present in Guix System for years, it was confronted with an uproar in its
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user base.
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In this post we look at why developers considered the initial behavior a
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“bug”, why users on the contrary had come to rely on it, and why
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developers remained blind to it. A patch to reinstate the initial
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behavior [is being reviewed](https://issues.guix.gnu.org/62584). This
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post is also an opportunity for us Guix developers to extend our
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apologies to our users whose workflow was disrupted.
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# The crux of the matter
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Anyone who’s used Guix System in the past has seen this message on the
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console during the boot process:
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```
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error in finalization thread: Success
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```
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The following picture shows a typical boot screen (with additional
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messages in the same vein):
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If you have never seen it before, it may look surprising to you. Guix
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System users lived with it literally for years; the message became a
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hint that the boot process was, indeed, successful.
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A few months ago, a contributor sought to satisfy their curiosity by
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finding the origin of the message. It did look like a spurious error
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message, after all, and perhaps the right course of action would be to
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address the problem at its root—or so they thought.
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As it turns out, the message [originated in
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Guile](https://git.savannah.gnu.org/cgit/guile.git/tree/libguile/finalizers.c#n238?id=df86a2a8c8725ac6244a222d399a5b959101f621)—check
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out the [Guile
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manual](https://www.gnu.org/software/guile/manual/html_node/Foreign-Object-Memory-Management.html)
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if you’re curious about finalization. Investigation revealed two
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things: first, that this `perror` call in Guile was presumably reporting
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the wrong error code—this was
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[fixed](https://git.savannah.gnu.org/cgit/guile.git/commit/?id=1fbe89f7bdbf35408ec2df8de755c2f1323016a6).
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The second error—the core of the problem—lied in Guix System itself.
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Remember that, in its quest of memory safety™, statelessness, and fun,
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Guix System does it all in Guile Scheme—well, except for the kernel (for
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now). As soon as Linux has booted, Guix System spawns Guile to run boot
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code that’s in its [*initial RAM
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disk*](https://guix.gnu.org/manual/en/html_node/Initial-RAM-Disk.html)
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(“initrd”). Right before executing
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[`shepherd`](https://gnu.org/software/shepherd), its service manager, as
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PID 1, the initrd code would carelessly close all the file descriptors
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above 2 to make sure they do not leak into PID 1. The problem—you
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guessed it—is that one of them was the now-famous file descriptor of the
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finalization thread’s pipe; the finalization thread would quickly notice
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and boom!
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```
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error in finalization thread: Success
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```
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Our intrepid developers thought: “hey, we found it! Let’s fix it!”. And
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so [they
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did](https://git.savannah.gnu.org/cgit/guix.git/commit/?id=168a7933c0e138dc7061a3f0dc96871e16da5c5f).
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# Breaking user workflows
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This could have been the end of the story, but there’s more to it than
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software. As Xkcd [famously captured](https://xkcd.com/1172/), this was
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bound to break someone’s workflow. Indeed, had developers paid more
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attention to what users had to say, they would have *known* that the
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status quo was preferable.
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For some time now, users had shown that they held the error/success
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message deep in their heart. The message was seen on the blackboard at
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the [Ten Years of Guix](https://10years.guix.gnu.org) celebration, as a
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motto, as a rallying cry, spontaneously put on display:
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What’s more, a fellow NixOS hacker and Guix enthusiast, beguiled by this
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powerful message, [designed](/static/blog/img/error-success-sticker.svg)
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stickers and brought them to FOSDEM in February 2023:
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The sticker design builds upon the “test pilot” graphics made by Luis
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Felipe for the [1.3.0
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release](https://guix.gnu.org/en/blog/2021/gnu-guix-1.3.0-released/).
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The test pilot has a bug on its helmet. In a way, the drawing and error
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message both represent, metaphorically, a core tenet of Guix as a
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project; just like Haskell is *avoiding success at all costs*, Guix
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seems trapped in an *error/success* quantum state.
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Had it gone too far? Was calling it a “bug” the demonstration of the
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arrogance of developers detached from the reality of the community?
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# Fixing our mistakes
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Those who installed Guix System starting from [version
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1.4.0](https://guix.gnu.org/en/blog/2022/gnu-guix-1.4.0-released/) have
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been missing out on the error/success boot message. The patch
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[submitted today](https://issues.guix.gnu.org/62584) finally reinstates
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that message. The review process will determine whether consensus is to
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enable it by default—as part of
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[`%base-service`](https://guix.gnu.org/manual/en/html_node/Base-Services.html#index-_0025base_002dservices-1)—or
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whether to make it optional—after all, we also need to accommodate the
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needs of *new* users who never saw this message. This will allow users
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to restore their workflow, while also ensuring that those freshly
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printed stickers remain relevant.
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This incident had broader consequences in the project. It led some to
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suggest that we, finally, set up a *request-for-comment* (RFC) kind of
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process that would give all the community a say on important topics—a
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process most large free software projects have developed in one form or
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another. Such a process could have prevented this incident: instead of
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arrogantly labeling it as a “bug”, developers would have proposed an RFC
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to remove the message; the discussion period, most likely, would have
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made it clear that removal was not a desirable outcome and we would all
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have moved on.
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This incident made many users uncomfortable, but we are glad that it is
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now being addressed. The lessons learned will be beneficial to the
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project for the years to come.
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# Credits
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> [Test
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> pilot](https://git.savannah.gnu.org/cgit/guix/guix-artwork.git/tree/promotional/)
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> by Luis Felipe distributed under the terms of
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> [CC-BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/);
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> sticker design distributed under
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> [CC-BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/) as
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> well. Blackboard picture by Julien Lepiller under
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> [CC0](https://creativecommons.org/publicdomain/zero/1.0/); sticker
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> pictures under
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> [CC0](https://creativecommons.org/publicdomain/zero/1.0/).
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>
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> Many thanks to the anonymous sticker provider!
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#### About GNU Guix
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[GNU Guix](https://guix.gnu.org) is a transactional package manager and
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an advanced distribution of the GNU system that [respects user
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freedom](https://www.gnu.org/distros/free-system-distribution-guidelines.html).
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Guix can be used on top of any system running the Hurd or the Linux
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kernel, or it can be used as a standalone operating system distribution
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for i686, x86_64, ARMv7, AArch64 and POWER9 machines.
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In addition to standard package management features, Guix supports
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transactional upgrades and roll-backs, unprivileged package management,
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per-user profiles, and garbage collection. When used as a standalone
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GNU/Linux distribution, Guix offers a declarative, stateless approach to
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operating system configuration management. Guix is highly customizable
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and hackable through [Guile](https://www.gnu.org/software/guile)
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programming interfaces and extensions to the
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[Scheme](http://schemers.org) language.
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