Re: Appled

Si, parmi les systèmes d'init launchd est la principale source d'inspiration de systemd. C'est encore plus apparent sur ce billet qui a introduit systemd en 2010.

But first, let's clear a few things up: is this kind of logic new? No, it certainly is not. The most prominent system that works like this is Apple's launchd system: on MacOS the listening of the sockets is pulled out of all daemons and done by launchd. The services themselves hence can all start up in parallel and dependencies need not to be configured for them. And that is actually a really ingenious design, and the primary reason why MacOS manages to provide the fantastic boot-up times it provides. I can highly recommend this video where the launchd folks explain what they are doing. Unfortunately this idea never really took on outside of the Apple camp.

The idea is actually even older than launchd. Prior to launchd the venerable inetd worked much like this: sockets were centrally created in a daemon that would start the actual service daemons passing the socket file descriptors during exec(). However the focus of inetd certainly wasn't local services, but Internet services (although later reimplementations supported AF_UNIX sockets, too). It also wasn't a tool to parallelize boot-up or even useful for getting implicit dependencies right.

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For socket activation we support full compatibility with the traditional inetd modes, as well as a very simple mode that tries to mimic launchd socket activation and is recommended for new services.

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The problem set of a session manager and an init system are very similar: quick start-up is essential and babysitting processes the focus. Using the same code for both uses hence suggests itself. Apple recognized that and does just that with launchd. And so should we: socket and bus based activation and parallelization is something session services and system services can benefit from equally.

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Later on, we will publish a longer guide explaining and suggesting how to write a daemon for use with this systemd. Basically, things get simpler for daemon developers:

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Note that systemd supports daemons not written in this style perfectly as well, already for compatibility reasons (launchd has only limited support for that). As mentioned, this even extends to existing inetd capable daemons which can be used unmodified for socket activation by systemd.

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If you love Apple launchd so much, why not adopt that?

launchd is a great invention, but I am not convinced that it would fit well into Linux, nor that it is suitable for a system like Linux with its immense scalability and flexibility to numerous purposes and uses.

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Well, before we started this we actually had a very close look at the various systems, and none of them did what we had in mind for systemd (with the exception of launchd, of course). If you cannot see that, then please read again what I wrote above.

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the point of the part about Upstart above was to show that the core design of Upstart is flawed, in our opinion. Starting completely from scratch suggests itself if the existing solution appears flawed in its core. However, note that we took a lot of inspiration from Upstart's code-base otherwise.