How can a program detect if it is running as a systemd daemon?

Question

Is there any way to detect in a program that it is run by systemd as a daemon?

systemd API

sd_booted()

is used to detected if the whole system is booted by systemd, but says nothing about the program itself.

Thanks

Answer 1

Get the parent process id and see whether that process is systemd.

Answer 2

You could set a magic environment variable in the daemon's service file and look for this variable.