On a systemd operating system there may or may not be a program called "init" and it may or may not be an alias for a systemd program. (One's operating system could be one of the ones that just invokes "/lib/systemd/systemd" directly without an "init" at all; or "init" could be Upstart or van Smoorenburg init or the nosh system manager; and of course just running unadorned "init" assumes that "/sbin" is on an unprivileged user's PATH.)
The best command to invoke here is either "systemctl" or "systemd".