sd_booted - Test whether the system is running the systemd init system
sd_booted() checks whether the system was booted up using the systemd
On failure, this call returns a negative errno-style error code. If the system
was booted up with systemd as init system, this call returns a positive return
value, zero otherwise.
These APIs are implemented as a shared library, which can be compiled and linked
to with the libsystemd pkg-config(1) file.
Internally, this function checks whether the directory
/run/systemd/system/ exists. A simple check like this can also be
implemented trivially in shell or any other language.