sd_booted - Test whether the system is running the systemd init system
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
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.