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.

> libsystemd links to liblzma for other features not related to notifications

Which is pretty emblematic of systemd's primary architectural fault!

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...

Strange protocol. Why not pass a path to a file that should be `touch`d and/or written to, I wonder? Would avoid the complexity of sockets.