Suricata

https://www.freedesktop.org/software/systemd/man/devel/sd_notify.html#Notes

"PSA: In context of the xzpocalypse we now added an example reimplementation of sd_notify() to our man page:

https://www.freedesktop.org/software/systemd/man/devel/sd_notify.html#Notes

It's pretty comprehensive (i.e. uses it for reload notification too), but still relatively short.

In the past, I have been telling anyone who wanted to listen that if all you want is sd_notify() then don't bother linking to libsystemd, since the protocol is stable and should be considered the API, not our C wrapper around it. After all, the protocol is so trivial"
From: https://mastodon.social/@pid_eins/112202687764571433