The programsystemdis the process with process ID 1. It is responsible for initializing the system in the required way.systemdis started directly by the kernel and resists signal9, which normally terminates processes. All other programs are either started directly by systemd or by one of its child processes.

The system initialization system used in SLES 15 is systemd. It is a modern and powerful system and service manager that replaces the traditional init system. It provides faster boot times, better dependency handling, parallelization, and more features and capabilities. Reference: https://documentation.suse.com/sles/15-SP3/html/SLES-all/cha-systemd-basics.html