Linux Bootup Process

1. Hardware poweron
   > hardware test, load BIOS
   > Find boot device (harddisk, cdrom, usb...)

2. Load harddisk & Boot loader (GRUB)
   > Execute boot loader in MBR
   > Boot menu select OS
   > The MBR then needs to know which partitions on the disk have boot loader code specific to their operating systems in their boot sectors and then attempts to boot one of them.

3. Load kernel
   > Load kernel into memory
   > Detect hardware and load the driver
   > pass control on to the kernel

4. Kernel init task
   > Establish memory management
   > detects the type of CPU
   > any additional functionality
  
5. Run the /sbin/init program
   > system check
   > verify the integrity of the file systems
   > start vital programs for operating system to function properly.
   > Inspects the /etc/inittab file to determine operation mode or runlevel
   > launch process depend on runlevel

6. System initialization
   > run /etc/rc.d/rc.sysinit

7. Init run level service

8. Init run file in /etc/rc.d/rc.local

9. Init prepare login environment and wait user login