Libsystemd is a grabbag utility library, and completely optional:
> The libsystemd library provides functions that allow interacting with various interfaces provided by the systemd(1) service manager, as well as various other functions and constants useful for implementing services in general.
> The libsystemd library provides functions that allow interacting with various interfaces provided by the systemd(1) service manager, as well as various other functions and constants useful for implementing services in general.
https://www.freedesktop.org/software/systemd/man/latest/libs...
E.g. the service readiness protocol is pretty trivial to implement yourself if you don't want to pull libsystemd as dep.