Debian: Init Interfaces–Our Users *and* Free Software

Recently, I’ve been watching the Debian Schadenfreude related to init systems. For those who do not know, Debian is trying to decide whether Systemd or Upstart will be used to start software on Debian. There are two other options, although I think Systemd and Upstart are the main contenders. Currently the Technical Committee is considering the issue, although there’s some very real chance that the entire project will get dragged through this swamp with the general resolution process. This is one of those discussions that proves that Debian truly is a community: if we didn’t have something really strong holding us together we’d never put up with something this painful. Between the accusations that our users now know the persecution European pagans faced at the hands of Christians as the Systemd priests drive all before them, a heated discussion of how the Debian voting system interacts with this issue, two failed calls for votes, a discussion of conflicts of interests, and a last-minute discussion of whether the matter had been appropriately brought before the Technical committee (and if so, under what authority), there’s certainly schadenfreude to go around if you’re into that sort of thing.

However, through all this, the Technical Committee has been doing great work understanding the issues; it has been a pleasure to watch their hard work from the side lines. I’d like to focus on one key question they’ve found: how tightly can other software depend on the init system. Each init system offers some nice features. Upstart has an event triggering model. Systemd manages login sessions and at least in my opinion has a really nice service file format. Can I take advantage of these in my software. If I do, then users of my software might need to use a particular init system. Ian Jackson argues that we should give our users the choice of what init system to run. He reminds us that Debian is a community that supports diversity and diverse goals. We support multiple desktop systems, web browsers, etc. Wherever we can, we support people working on their goals and give developers the opportunity to make it work. When developers succeed, we give our users the opportunity to choose from among the options that have been developed.

I think of Ian’s argument as an appeal to part of our Social Contract. Clause 4 of the social contract begins:

Our priorities are our users and free software.
We will be guided by the needs of our users and the free software community. We will place their interests first in our priorities. We will support the needs of our users for operation in many different kinds of computing environments.

Ian is right that our users will be served by choice in init systems. However, this trade off needs to be balanced against the needs of the free software community. Diversity is an important goal but it should not come at the price of stagnation and innovation. If I want to avoid using init scripts because they don’t provide restart on failure, because they are hard to write correctly, and because they don’t provide access to modern security isolation techniques, I should be able to do that. If Systemd service files provide a superior solution, I should be able to work toward using them. If the desire for init system diversity shuts down my ability to find like-minded people who want to take advantage of improvements in init systems and work towards that goal, then we’ve significantly damaged Debian as a forum for technical cooperation.

Early in my work as a Debian Developer, Anthony Towns taught me an interesting principle. Those who do the work get significant influence over how and what gets done. Ian’s right that we need to enable people to work towards choice in init systems. Those like-minded people need to be given a chance to find each other and pursue their goal. However the cost of success should be on the shoulders of those who value choice in init systems. It should not come at the cost of preventing people from depending on improvements in init systems.

The best proposal I’ve seen for balancing this is to enumerate stable interfaces that people want to use. Things like the logind interface or my favorite the service file interface. It needs to be possible to make another implementation of the interface. The interface needs to be stable enough that a dedicated team could have a chance of catching up with an implementation. At some point during the release cycle such interfaces would need to be frozen. However, I don’t think it is reasonable to mandate that there are multiple implementations of the interface, only that there could be. The point is to give people a chance to work towards diversity in init systems, not to force it down peoples’ throats kicking and screaming until they leave the project or ignore our processes. Steve Langasek and Colin Watson seem to be working towards this.

It’s possible there’s another approach besides interfaces. My main concern is the same as Ian’s: maintain Debian as a forum for people to pursue their goals and work together. I suspect we see the conflict in these goals differently. I hope that we as a project can explore this conflict and figure out where we have common ground. I commit to exploring how we can work towards init choice in my frameworks; I ask those who prioritize init choice to commit to explore how we can take advantage of new features in their framework.

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