Fedora 12 Initialization Process

MBR and kernel

1. BIOS (Basic Input Output System) is the lowest interface between the computer and peripherals. It performs integrity checks on memory and seeks intructions on the MBR (Master Boot Record) on the floppy or hard drive.
2. The MBR points to the GRUB boot loader.
3. The boot loader then asks the OS label which will identify which kernel to run and where it is located. The installation process requires to create/identify the partition and where to install the OS. GRUB are also configured during this process.
4. The boot loader then loads the operating system.
5. The first thing the kernel does is to execute init program. Init is the parent of all processes executed on linux.
6. The first process that init starts is a script /etc/rc.sysinit. The script file then directs init to:
1. Runs /etc/sysconfig/network. NETWORKING variable tells the kernel whether networking function should be activated or not, and HOSTNAME variable contains your computer's hostname and domain name,
2. Mounts filesystems defined in /proc/mounts,
3. Mounts USB filesystems defined in /proc/bus/usb directory,
4. Prints banner contains in /etc/redhat-release,
5. Initializes kernel parameter at runtime by reading /proc/modules configuration file,
6. Initializes user-defined modules from /etc/sysconfig/modules directory,
7. Sets device mapper multipath from /etc/multipath.conf configuration file,
7. Based on the appropriate run-level, several scripts are executed to start various processes to make the system functional.

1. The init process is the last step in the boot process and is identified by process id '1'. init is responsible for starting the system processes as defined in the /etc/inittab. init typically will start multiple instances of getty which waits for console logins which spawns one's shell process. Upon shutdown, init controls the sequence and processes for shutdown. The init process is never shut down. It is a user process and not a kernel system process, although it does run as root.