Linux Booting Process

Grub located at  Grub located at  /boot/grub/grub.conf  and lnked to /etc/grub.conf
● If MBR on /dev/hda is corrupted, reinstall the first stage bootloader with: /sbin/grub-install /dev/hda

BIOS:

Basic input and output system will load  Performs Systemintegrity check Searches, loads and executes the boot loader program ” BIOS loads and executes the MBR boot loader”

MBR:

Master boot record – which will have 446Bytes in size first sector of the HDD.
446 MBR (primary boot loader info)64 Partition Table 2 Active Sign (mbr validation check in last 2 bytes.) “MBR loads and executes the GRUB boot loader”

GRUB

(GRand Unified Boot Loader) :If you have multiple kernel images installed on your system, you can choose which one to be executed.
“GRUB just loads and executes Kernel and initrd images.”
initial RAM disk (initrd) is a temporary root file system that is mounted during system boot to support the two-state boot process. The initrd contains various executables and drivers that permit the real root file system to be mounted, after which the initrd RAM disk is unmounted and its memory freed.
The initrd contains a minimal set of directories and executables to achieve this, such as the insmod tool to install kernel modules into the kernel.

Kernel:

Mounts the root fle system   “Executes the /sbin/init program”Init: locks at the /etc/inittab file to decide the lnux run level

Run levels:

” run level programs are executed from /etc/rc.d/rc*.d/” 0 – Shutdown/Halt/Power off  1 – Single User Mode  2 – Multiple user without Network  3 – Multiple users with Network (CLI)  4 – Unused  5 – GUI mode  (X11) 6 – Reboot
Managing the initrd Image The initial RAM disk provides modules loaded early in the boot process. This file is located under /boot/initrd-$(uname -r).img Extra modules sometimes need to be added due to:  New hardware added to the system. i.e. SCSI controller New features needed such as USB devices.  Module needs to load automatically at boot time.Use mkinitrd and the –with option to rebuild with an extra module:mkinitrd –with=module_name /boot/initrd-$(uname -r).img $(uname -r)
System Processes: Process ID Description 0 The Scheduler  1 The init process    2 kflushd    3 kupdate    4 kpiod    5 kswapd    6 mdrecoveryd