Managing Services with systemd
Photon OS manages services with systemd. By using systemd, Photon OS adopts a contemporary Linux standard to bootstrap the user space and concurrently start services. This is an architecture that differs from traditional Linux systems such as SUSE Linux Enterprise Server.
A traditional Linux system contains an initialization system called SysVinit. With SLES 11, for instance, the SysVinit-style init programs control how the system starts up and shuts down. Init implements system runlevels. A SysVinit runlevel defines a state in which a process or service runs.
In contrast to a SysVinit system, systemd defines no such runlevels. Instead, systemd uses a dependency tree of targets to determine which services to start when. Combined with the declarative nature of systemd commands, systemd targets reduce the amount of code needed to run a command, leaving you with code that is easier to maintain and probably faster to execute. For an overview of systemd, see systemd System and Service Manager and the man page for systemd.
On Photon OS, you must manage services with systemd and systemctl, its command-line utility for inspecting and controlling the system, and not the deprecated commands of init.d.
For more information, see the index of all the systemd man pages, including systemctl, at https://www.freedesktop.org/software/systemd/man/