First, the boot process
1, BIOS: BIOS is input into the present output system. After the boot server host, will be based BIOS setting to host only the CPU memory card, keyboard and other equipment preliminary testing, testing has been successfully handed over control of the system according to the preset startup sequence, failure detection will (1) via a display screen or ( 2) buzzer alarm, and more time will be handed over to the local hard disk. You may store the hardware configuration information, independent battery power supply. BIOS battery discharge can restore factory settings.
BIOS functions: (1) Power On Self Test (2) hardware initialization (3) to boot the operating system (the BOOT)
2, the guide MBR: when starting a program from the local hard drive, first, the first sector of the hard disk in accordance with the MBR is provided, to transfer control to the system partition (/ boot) comprising an operating system boot files; or directly recording the MBR the soundtrack information call the start menu. (GRUB)
3, GRUB menu: For Linux operating systems. GRUB is the most widely used multi-system boot program. After the transfer system control to GRUB, the boot menu will be displayed to the user selected, and depending on the option to load the Linux kernel files, then the system control to the kernel. Note that, CentOS7 uses GRUB2 boot loader.
4, load the Linux kernel: Linux kernel is a special pre-compiled binary files between various hardware resources and system programs, responsible for resource allocation and scheduling. After the kernel took control of the system, will fully grasp the whole process of running the Linux operating system. In CentOS system, the default kernel file is located in "/boot/VMLinuz-3.10.0.el7.x86_64"
5, init process initialization: