sd_booted — Test whether the system is running the systemd init system
#include <systemd/sd-daemon.h>
| int sd_booted( | void ); | 
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.
This function is provided by the reference implementation of APIs for new-style daemons and distributed with the systemd package. The algorithm it implements is simple, and can easily be reimplemented in daemons if it is important to support this interface without using the reference implementation.
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.
For details about the algorithm check the liberally licensed reference implementation sources: http://cgit.freedesktop.org/systemd/systemd/plain/src/libsystemd-daemon/sd-daemon.c and http://cgit.freedesktop.org/systemd/systemd/plain/src/systemd/sd-daemon.h
sd_booted() is implemented
                in the reference implementation's
                sd-daemon.c and
                sd-daemon.h files. These
                interfaces are available as shared library, which can
                be compiled and linked to with the
                libsystemd-daemon
                pkg-config(1)
                file. Alternatively, applications consuming these APIs
                may copy the implementation into their source
                tree. For more details about the reference
                implementation see
                sd-daemon(3).
If the reference implementation is used as drop-in files and -DDISABLE_SYSTEMD is set during compilation this function will always return 0 and otherwise become a NOP.