Is that protocol documented/stable? For whatever reason, daemons are choosing to link to libsystemd instead of implementing it themselves.
It doesn't matter that libsystemd links to liblzma for other reasons. It's still in the address space of any daemon that is using libsystemd for the notification protocol.
I know Golang has their own implementation of sd_notify().
For Slurm, I looked at what a PITA pulling libsystemd into our autoconf tooling would be, stumbled on the Golang implementation, and realized it's trivial to implement directly.
Caveat is that golang is not a good enough actor to be a reliable indicator of whether this interface is supported, though. They’ll go to the metal because they can, not because it’s stable.
The funny thing is that libsystemd _used_ to be split into several different libraries. I certainly remember libsystemd-journal (which is presumably the part of libsystemd that pulls in liblzma) being separate to libsystemd-daemon (which is the part that implements sd_notify, as used by OpenSSH [after patching by distros]).
If that split had never happened, then liblzma wouldn't have ended up being linked into sshd...
Services may be in a different mount namespace from systemd for sandboxing or other reasons (also means you have to worry about filesystem permissions I suppose). Passing an fd from the parent (systemd) is a nice direct channel between the processes
