Writing systemd units that stop gracefully before shutdown
1–10 of 57 posts
Re: Writing systemd units that stop gracefully before shutdown
#2No post body was provided.
Re: Writing systemd units that stop gracefully before shutdown
#3I love this. Lots of details I didn't know.
Re: Writing systemd units that stop gracefully before shutdown
#4Halt is apparently not the same as poweroff.
Re: Writing systemd units that stop gracefully before shutdown
#5Halt is apparently not the same as poweroff.
A "halt -fp" just unmounts file systems and immediately shuts down.
I find that CentOS systems that I've used for a while seem to hang on shutdowns; halt -fp is a way to get them down quickly. It is important to terminate any sensitive processes beforehand.
Re: Writing systemd units that stop gracefully before shutdown
#6A much more challenging task is writing a systemd unit that starts gracefully before shutdown. I wanted to write a unit that could issue an API call to delete the instance rather than doing a normal power off. Putting it at a reasonable place in the sequence took a lot of trial and error! The trick is actually to have the unit be started at some point in normal boot up (e.g. “armed”) and then do the actual task when the unit is stopped.
Here’s the unit I ended up with: https://github.com/CGamesPlay/infra/blob/master/private-serv...
Re: Writing systemd units that stop gracefully before shutdown
#7A much more challenging task is writing a systemd unit that starts gracefully before shutdown. I wanted to write a unit that could issue an API call to delete the instance rather than doing a normal power off. Putting it at a reasonable place in the sequence took a lot of trial and error! The trick is actually to have the unit be started at some point in normal boot up (e.g. “armed”) and then do the actual task when…
That's what this post builds to solving at the end and in the next post - having a unit deletes the instance from a cluster before shutdown
Re: Writing systemd units that stop gracefully before shutdown
#8A much more challenging task is writing a systemd unit that starts gracefully before shutdown. I wanted to write a unit that could issue an API call to delete the instance rather than doing a normal power off. Putting it at a reasonable place in the sequence took a lot of trial and error! The trick is actually to have the unit be started at some point in normal boot up (e.g. “armed”) and then do the actual task when…
I tend to push the metaphor of software being meant to be read and only incidentally to be run by a computer as far as I can. We are telling a story to future us or our successors. Stories have rules and it's jarring when you violate them.
There's an idea in software that's a bit like the corollary of Chekhov's gun. Chekhov's gun is about not presaging jarring story elements that will never come to pass. But it's nearly as jarring to leave important story arcs as complete surprises until the end. Producing the gun moments before the curtain goes down would be quite a WTF. We didn't know that was a possibility. That's a niche that some people occupy, but it is a niche.
Introducing things early fights with Locality of Reference, but when we're talking about things of deep, dramatic importance (like an attempted murder, or a reaper process) it's important to introduce that "character" early in the story so that people know that it exists. Failing to do so is a form of deus ex machina and we only appreciate that in very small doses.
So framed that way, I don't see a problem with having to start a killswitch while you're spinning everything up. It's there, people can see it, and know to ask questions about it.
Re: Writing systemd units that stop gracefully before shutdown
#9Halt is apparently not the same as poweroff.
A "halt -fp" just unmounts file systems and immediately shuts down. I find that CentOS systems that I've used for a while seem to hang on shutdowns; halt -fp is a way to get them down quickly. It is important to terminate any sensitive processes beforehand.
For systems that hang or take intolerably long to shutdown, I typically do:
systemctl --force [poweroff|reboot]
Re: Writing systemd units that stop gracefully before shutdown
#10A much more challenging task is writing a systemd unit that starts gracefully before shutdown. I wanted to write a unit that could issue an API call to delete the instance rather than doing a normal power off. Putting it at a reasonable place in the sequence took a lot of trial and error! The trick is actually to have the unit be started at some point in normal boot up (e.g. “armed”) and then do the actual task when…
[deleted]