Want to understand about kured reboot-sentinel

[dharsanb]

https://github.com/kube-hetzner/terraform-hcloud-kube-hetzner/blob/db33eeedc367831995122b72d8a10cc7c6aa5e3c/locals.tf#L905
In the above line, I wanted to understand how the file /sentinel/reboot-required is populated. I couldn't find any documentation on it being a part of MicroOS. I know I'm missing some context but wanted to understand if reboot-sentinel option is getting replaced somewhere else in terraform or the file is populated by some daemon running on the host.
Thanks.

[dharsanb]

Found it. It's because host path /var/run is mounted at /sentinel.