Delay being killed on reboot/poweroff

[champtar]

Setting KillSignal=SIGCONT is a hack, but it gives us DefaultTimeoutStopSec before being killed (45s on Fedora, 90s on EL9).
The proper systemd way would be to use inhibit locks but they are ignored by reboot/poweroff commands, ie you need the systemctl reboot/poweroff variants, and just using systemd-inhibit makes all the logs starts with systemd-inhibit instead of bootupctl.

[openshift-ci]

Hi @champtar. Thanks for your PR.

I'm waiting for a coreos member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[cgwalters]

Thanks for the patch! I'd prefer to have us explicitly ignore SIGTERM in our own code.

[champtar]

Thanks for the patch! I'd prefer to have us explicitly ignore SIGTERM in our own code.

If we want to fully integrate with systemd, we can use sd_notify() and send EXTEND_TIMEOUT_USEC= (https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#EXTEND_TIMEOUT_USEC=%E2%80%A6)

If we just ignore SIGTERM, we must set KillMode=mixed so that subprocess do not also get SIGTERM (https://www.freedesktop.org/software/systemd/man/latest/systemd.kill.html#KillMode=)

I'm hello world level in rust so if someone wants to implement this please go ahead

[cgwalters]

Moving this to #812

Thanks again for submitting a patch though!