sd_booted (3) - Linux Man Pages
sd_booted: Test whether the system is running the systemd init system
sd_booted - Test whether the system is running the systemd init system
checks whether the system was booted up using the systemd init system.
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
Internally, this function checks whether the directory
exists. A simple check like this can also be implemented trivially in shell or any other language.