Which of the following are init systems used within Linux systems? (Choose THREE correct answers.)

startd is not a Linux init system - it resembles launchd (macOS) or Service Management Facility (Solaris) but does not exist as a Linux init daemon.

systemd is the current default init system on most modern Linux distributions including RHEL, Debian, Ubuntu, and Fedora, using unit files and parallel service startup.

Upstart is a real event-driven init daemon developed by Canonical, used in older Ubuntu (prior to 15.04) and older RHEL/CentOS releases as a transitional replacement for SysV init.

SysInit is not a real init system - the correct name for the traditional init is SysV init, and SysInit appears to be a distractor combining parts of that name incorrectly.

SysV init is the traditional Unix System V initialization daemon that manages services through sequential runlevel-based shell scripts in /etc/init.d and was the standard Linux init for decades.