Which of the following files starts the initialization process in booting sequence of the Linux operating system?

After the Linux kernel completes hardware initialization and mounts the root filesystem, it executes /sbin/init as PID 1 - the first and only process directly launched by the kernel. This init program then reads its configuration and spawns all other system processes and services, making it the true starting point of the userspace initialization sequence.

/etc/inittab is a configuration file that the init program reads to determine runlevel actions and service startup order; it is a data file consumed by init, not the program that starts initialization.

rc.local is a shell script executed near the very end of the boot sequence for local administrator customizations, running long after initialization has already begun.

rc.sysinit is a script invoked by init to perform early system tasks such as mounting filesystems and setting the hostname, but it runs only after init itself has already started as PID 1.