What is the first process that the Linux kernel runs when it boots on most Linux systems?

The first process that the linux kernel runs when it boots on linux system is the "/sbin/init process"

Explanation:

The first process of the Linux boot process is the execution of the boot loader, the boot loader is responsible for locating and loading the kernel. The kernel is the core of the operating system and can be located in the / boot directory. Next, the initrd is loaded. The initrd file consists of device drivers, file system modules, logical volume modules, and other items required for boot but not built directly into the kernel.

As soon as the kernel and initial ramdisk are loaded, the kernel goes ahead to initialize the system hardware. After this, the kernel begins executing what we know as the operating system, starting the / sbin/init process.