SYSTEMD-UD...E.SERVICE(8)

👑 SYSTEMD-UD...E.SERVICE(8) 👑

okay bestie, we're talking about systemd-udev-settle.service — she's a little unit from the systemd girlies, and she has OPINIONS attached to her. let's get into it 💅

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✨ NAME ✨

systemd-udev-settle.service — the girl whose whole job is waiting for all the pending udev events to get handled 🫶

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🌸 SYNOPSIS 🌸

systemd-udev-settle.service

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💖 DESCRIPTION 💖

so basically, this service calls udevadm settle, and that call just sits there and waits until every single event that udev(7) has queued up has actually been processed. that's it. that's the whole vibe. it's a crude way of waiting until "all" hardware has been discovered — and yes, the scare quotes around "all" are doing a LOT of work there, iykyk.

the idea is that other services can pull this one in and then order themselves after it, so they know the udev queue is empty before they do their thing. sounds cute, right?

🚨 okay so here's the thing: using this service is not recommended. like, at all. periodt.

why? because there is no guarantee whatsoever that hardware is fully discovered at any specific time. none. zero. the kernel does hardware detection asynchronously, and some buses and devices take a genuinely very long time to become ready — and on top of all that, extra hardware can get plugged in at any time, because of course it can. 🙈

so instead of this whole situation, services should subscribe to udev events and react to any new hardware as it's discovered, live, in real time, main character energy. and services that — based on their configuration — expect certain devices to show up, they may warn or report a failure after a timeout. that timeout should be tailored to the hardware type. like, customize it. make it make sense for your hardware. 🎀

also, waiting for systemd-udev-settle.service usually slows boot significantly, because it means you're waiting for all the unrelated events too. all of them. the ones you don't even care about. it's giving "standing in line at the DMV for something that has nothing to do with you." 😭

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🔥 SEE ALSO 🔥

• udev(7)
• udevadm(8)

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and that's the tea, bestie 🍓 this page came to you courtesy of systemd 262.1 — go forth and subscribe to udev events instead, mwah 💜✨