Initrd

• this file is a gzipped cpio archive known as an initramfs file, and it contains a basic, small Linux root file system.

• as the kernel boots, it extracts the initramfs file into RAM and then runs a script called init in the root of that initramfs.

• this script is a standard shell script that does hardware detection, creates some mount points, and then mounts the root file system.

• the kernel knows where the root file system is, because it was passed as one of the boot arguments (root=) by GRUB when it first loaded the kernel

• the final step for the initramfs file after it mounts the real file system is to execute the /sbin/init program, which takes over the rest of the boot process.

• /sbin/init is the parent process of every program running on the system

• always has a PID of 1 and is responsible for starting the rest of the processes that make up a running Linux system.