Order of the Boot Process
n BIOS initialization
n Peripherals detected, boot device selected ,
first sector read of d
n Boot loader configuration [
GRUB initialization ]
n Stage 1 : small, resides in MBR or boot sector
contains information about only Stage 2 and loads the stage 2
n Stage 2: This is the core image of GRUB reads
the file
n Grub.conf [
/boot/grub/grub.conf ] symbolic link [ /etc/grub.conf ]
n Kernel Loading
n Init Process [ /sbin/init ]
l Starting init also loads [
/etc/inittab ] file into memory
n rc loading [ /etc/rc.d/rc ]
n rc.sysinit loading for
interactive startup [ /etc/rc.d/rc.sysinit ]
n System reads the file [
/etc/fstab ] to mount system partitions
n rc reads /etc/inittab file
to load default or selected run level and Enter to selected run level
n rc.local for user defined
scripts [ /etc/rc.d/rc.local ]
n Loads the X server [ If
Run Level 5 is selected ]
l prefdm script loads [ /etc/X11/prefdm ]
l prefdm reads the file /etc/sysconfig/desktop file
to load display mangers such as kdm,gdm,xdm
l Then system reads file [ /etc/X11/xorg.conf
] this specifies the hardware components resources
l Monitor
l Keyboard
l Mouse
l Display Adaptor
GRUB and grub.conf
n GRUB – GRand Unified Bootloader Grub is more powerful and
we can edit the Grub
l Command-line interface
available at boot prompt
l Boot form ext2/ext3,
ReiserFS, FAT file systems
l Supports MD5 password
protection
n /boot/grub/grub.conf
n Configuration file provides
the information about kernel location
and other parameters to load operating
system
n Chain-loading is used for
loading other operating system.
Set the password on grub
# grub-md5-crypt
Password redhat
Retype password redhat
It will show the encrypted form of password copy
that line and paste in following file........
#vim /boot/grub/grub.conf
At the line on below hiddenmenu
hiddenmenu
Password --md5
(paste the line which is copied)
Save the file
Now your grub is password protected
Kernel Initialization:-
n Device detection.
n Device drive initialization.
n Mount root file system read
only.
n Load Initial Process.
Run Levels
n Run Levels are different
modes to run linux with different configuration. Init defines 0 to 6 run levels
n Defines in file [
/etc/inittab ]
n Following chard details the
run levels that linux defines by default:
n Runlevel Effect
n 0 Halt
n 1,s,emergency Single
user modes ( Only root user can be logged on. Used to perform
Maintenance )
n
2 Multi-user,
without NFS networking
n 3 Full
multi-user mode. ( Includes networking )
n
4 User
definable, but duplicate of run level 3
n 5 X11
( Includes networking )
n
6 Reboot
Note :- If there is no run level defined then system will
attempt to boot to run level 9 which is undefined.
Chaining the root password
Boot system into a single user mode
for change the root password
Reboot
the system and press
"a" on Grub main menu and
type "s" with one space
# setenforce
0
# passwd
#
setenforce 1
# reboot
Or # init 5
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