***************
\nSummary
\n=======<\/p>\n
A) START – BIOS (Basic Input Output System) = when BIOS load in RAM Called BOOT STARPPING – CMOS = Called this process KERNAL LANDING –
\n MBR in Hard Disk – BOOTLOADER – KERNEL – INITRD IMAGE – Inittab = Upto this process called USER LANDING<\/p>\n
B) There are two tyeps of boot loader in linux <\/p>\n
a) LILO
\n i) 1st stage
\n ii) 2nd stage<\/p>\n
b) GRUB
\n i) 1st stage
\n ii) 1.5 stage(This stage is optional)
\n iii) 2nd stage <\/p>\n
Scratch \\ start
\n============
\nA) Power on by USER<\/p>\n
B) Power goes into SMPS.<\/p>\n
C) Power goes into MOTHERBOARD.<\/p>\n
D) Power goes then into CPU’s single pin.<\/p>\n
E) Then CPU awakes BIOS.<\/p>\n
F) Bios goes into RAM and start POST (power on self test) —>means BIOS will
\n check all hardware and periferels. This step is called BOOTSTRAPPING.<\/p>\n
G) Then Bios goes into CMOS (Complementary metal.oxide.semiconductor) to check
\n the which device load in RAM. We can change the CMOS. CMOS is samll program
\n which take the information from Bios. CMOS battery supply power to CMOS
\n program. Therefore always change the CMOS battery after every 6 months.
\n Bios read the CMOS program for load the device.<\/p>\n
H) BIOS load first sector \/ first track \/ 0 cylinder of harddisk ie. MBR(master boot record) into RAM. <\/p>\n
a) MBR size is 512 MB. It divided into three parts:-
\n 1) Bootsector(446 bytes),partition table(64 bytes),magic number(2 bytes)
\n Where boot sector contains boot loader (LILO or GRUB for linux and NTLDR
\n for windows)
\n 2) Partion table contains 4 programs of 16 bytes.So we can create only 4
\n partition in a harddisk,ie four primary partition and last primary will
\n be extended by logical partition
\n 3) Magic number of 2 bytes contais 0 or 1.If 0 means no and 1 means yes.
\n If bootsector and partition table in MBR contains errors then magic
\n number will be 0 otherwise 1.<\/p>\n
##############################################################################
\n MBR(master Boot Record) First secter of harddisk=512 bytes
\n ********************************************
\n 446 bytes – Boot sector –
\n LILO or GRUB for linux and NTLDR for windows
\n =========================================================================== <\/p>\n
64 bytes – Partition table –
\n 1st primary partition 16 bytes
\n 2nd primary partition 16 bytes
\n 3rd primary partition 16 bytes
\n 4th primary partition 16 bytes \/ extended partition can be subdivided into logical partitions
\n ===========================================================================
\n 2 bytes – Magic number –
\n If bootsector and partition table in MBR contains errors |
\n then magic number will be 0 otherwise 1. <\/p>\n
#################################################################################<\/p>\n
I) Bios first check whether magic number is yes or no in MBR
\n If yes it will go for active partition in partition table else displays
\n error as boot failure. Active partition denoted by * in partition table
\n of linux and in windows C drive by default.<\/p>\n
J) Then goes into first sector of active partition and whatever finds in first
\n sector of active partition loads in RAM. But its same MBR are there. So
\n BIOS goes to boot sector of MBR. IN boot sector, there is boot-loader
\n LILO or GRUB for linux and TLDR for windows. Bios load LILO\/GRUB into RAM
\n for linux and ntldr for windows. NTLDR load windows.<\/p>\n
K) In linux ANACONDA INSTALLER load LILO\/GRUB in MBR while the time of
\n installation. LILO\/GRUB is powerfull than ntldr. In dual boot first install
\n windows then install linux.<\/p>\n
L) Bios load LILO\/GRUB into RAM. This is called the FIRST STAGE OF BOOT
\n PROCESS. The purpose of first stage to load Second Stage ie boot.b.<\/p>\n
M) LILO have a Map Code file. In this file have a address of ‘boot.b’ in CHS
\n format. LILO can not read this format. Therefore call the Bios to read
\n this file. If you change the path of LILO in configuration file then you
\n need to re-read LILO conf file. Using this command ‘\/$ lilo -v’<\/p>\n
N) Bios read map code and load BOOT.B file in RAM. This step called SECOND
\n STAGE OF BOOT PROCESS.<\/p>\n
O) Map and Message these two file locate in the Boot.b file. Once again boot.b
\n can’t read these two files, therefore boot.b file again call the Bios for
\n read this two files. Bios read this files and load into RAM. Message file
\n show the splash screen to select the OS.<\/p>\n
##########################################
\n Prompt message
\n ************
\n Timeout (in seconds)
\n Default OS (if you not select any os)<\/p>\n
=============================================
\n \/boot\/boot.b (2nd stage of boot loading)
\n =============================================
\n \/boot\/map | \/boot\/message
\n \/boot\/boot.0300 | \/boot\/boot.0800
\n =============================================<\/p>\n
###########################################<\/p>\n
P) After slecet the linux os boot.b load the Linux Kernal in RAM. Kernal
\n located in \/boot\/vmlinuz-2.4.20-8, in comparc’d format. At the loading time
\n LILO un-comparc’d it and load into RAM.
\n This steps called KERNEL LANDING.<\/p>\n
Q) Once kernel load into RAM then kernel himself load the INITRD IMAGE in RAM.
\n Initrd image also in comparc’d format. Initrd image have a linuxrc script.
\n Initrd image run the linuxrc script.<\/p>\n
R) Linuxrc script load ext3.o filesystem, jbd.o harddisk driver and others
\n *.o driver. Linuxrc script mount ‘\/’ as a read only partition, it is call<\/p>\n
S) Init – System Daemon this script run by linuxrc script
\n (located at \/sbin\/init )<\/p>\n
a) Inittab this is a script file at \/etc\/inittab<\/p>\n
1) check default runlevel<\/p>\n
2) RC.SYSINIT this is a important file for boot
\n processing. This file read only one time at the
\n booting time and located at \/etc\/rc.d\/rc.sysinit.
\n (as a sub-shell ). This script called ‘systemv’.<\/p>\n
i) Network – reload the \/etc\/sysconfig\/network this file
\n Set the hostname, this file run command $ hostname,
\n if hostname found then set it, else set the default
\n hostname i.e. ‘localhost’<\/p>\n
ii) mounts ‘\/proc’ filesystem (command mount -n -t proc \/proc \/proc)<\/p>\n
iii) \/etc\/init.d\/functions (same env)
\n After finish the proc mounting inittab run this file.
\n This cmd set around 23 functions.<\/p>\n
iv) global UMASK
\n v) global PATH
\n vi) defines 17 shell functions
\n 1) success
\n 2) failure
\n 3) passed
\n 4) warning
\n 5) echo_success
\n 6) echo_failure
\n 7) echo_passed
\n 8) echo_warning
\n 9) killproc
\n 10) pidofproc
\n 11) pidfileofproc
\n 12) action
\n 13) checkpid
\n 14) confirm
\n 15) status
\n 16) strstr
\n 17) daemon
\n vii) \/etc\/redhat-release
\n This cmnd display redhat version
\n which install your system.<\/p>\n
viii) Then display interactive mode to
\n customize start. Press ‘I’ option to
\n boot manually.<\/p>\n
ix) Set Localtime \/etc\/localtime
\n ‘hwclock’ & ‘date’ cmnd change
\n \/etc\/localtime & \/etc\/adjtime file.<\/p>\n
x) \/proc -to check kernel parameters<\/p>\n
xi) \/etc\/sysctl.conf -for kernal tunning<\/p>\n
xii) Keyboard Mapping<\/p>\n
xiii) FASTBOOT – if we create a blank
\n file as a ‘fastboot’ in ‘\/’ then
\n fsck not process<\/p>\n
xiv) \/etc\/sysconfig\/readonly-root
\n – rwtab file, all file system
\n mounted as a read only<\/p>\n
xv) \/etc\/rwtab.d\/* – some exceptional
\n files in read write mode<\/p>\n
xvi) FSCK – goto fstab and check the
\n parameter in 5th column if there are
\n ‘1’ then run fsck cmnd, else check
\n next line.<\/p>\n
xvii) Mounting tmpfs – \/dev\/shm shared
\n application memory.<\/p>\n
xviii) Read \/etc\/fstab file and remounts
\n ‘\/’ read-write mode and all others
\n partition.<\/p>\n
xix) Quota on.<\/p>\n
xx) Enableing SWAP partition.<\/p>\n
xxi) \/bin\/dmesg – \/var\/log\/dmesg
\n collect hardware info from
\n BIOS and display. <\/p>\n
b) RC scripts – \/etc\/rc.d\/rc ( as a subshell )
\n RC manage the which services started and which not started.
\n This script read any time.<\/p>\n
i) checks runlevel ( function )<\/p>\n
ii) finding previous runlevel<\/p>\n
iii) \/etc\/init.d\/functions (same env)<\/p>\n
iv) checks user confirmation mode and
\n interactive mode \/ startup. Setting new runlevel<\/p>\n
v) \/etc\/rc.d\/rc3.d\/K* (K – means stop)
\n This is used for stop. However here are 5 functions
\n 1) STOP
\n 2) START
\n 3) RESTART
\n 4) STATUS
\n 5) CONDRESTART<\/p>\n
vi) \/etc\/rc.d\/rc3.d\/S* (S – means start)
\n This is used for start only. Same as above. However
\n some files are in this directory, those are symblink
\n with some files that located in ‘\/etc\/init.d\/’. These
\n files called Init Script file. These files
\n run by \/etc\/init.d\/function cmd<\/p>\n
vii) \/usr\/bin\/rhgb-client functions,used only stop
\n ( start
\n stop
\n restart
\n status
\n condrestart )<\/p>\n
viii) \/etc\/rc.d\/rc.local this is a last file
\n run by rc script. If you want to run some cmnd
\n automatic then you can enter those cmnd or scirpt
\n in this file.<\/p>\n
c) Now part ofthe \/sbin\/init call \/etc\/inittab file. inittab read
\n \/sbin\/shutdown -t3 -r now
\n poweroff considerations – \/sbin\/shutdown -f -h +2
\n poweron considerations – \/sbin\/shutdown -c
\n power ok wait
\n Now inttab read following line in his file
\n 1:2345:respawn:\/sbin\/mingetty tty1
\n IF runlevel 5 then – \/etc\/X11\/predfm -nodaemon<\/p>\n
I) Inittab call MINGETTY
\n a) loads \/dev\/tty1
\n b) Reads \/etc\/issue file
\n c) \/bin\/login
\n 1) \/usr\/bin\/passwd
\n i)PAM (Plugabel Authantication Module) security.
\n ii) \/etc\/passwd
\n iii) \/etc\/shadow
\n iv) \/etc\/group
\n v) \/etc\/gshadow<\/p>\n
d) puts login daemon in sleep state<\/p>\n
e) root\/.hushlogin exists ? Ja! mail,motd,lastlog NOT RUN!<\/p>\n
f) \/etc\/motd (Message of the day)<\/p>\n
g) lastlog* using \/var\/log\/lastlog<\/p>\n
h) Checks user’s mail – \/var\/spool\/mail\/root<\/p>\n
i) wakes the \/bin\/login process which forks off as
\n independent application daemon & mingetty goes to Zombie state.<\/p>\n
2) login calls \/bin\/bash
\n puts login to sleep state<\/p>\n
3) \/etc\/profile (global sets HOSTNAME, HISTSIZE, PATH etc)
\n a) \/etc\/inputrc (sets keyboard mappings)
\n b) \/etc\/termcap (sets term. capabilities)
\n c) \/etc\/profile.d\/*.sh ( 13 files )
\n customize *.sh files
\n ( colorls.sh
\n vim.sh
\n glib2.sh
\n gnome-ssh-askpass.sh
\n krb5.sh
\n lam.sh
\n lang.sh
\n less.sh
\n mc.sh
\n pvm.sh
\n qt.sh
\n vim.sh
\n which-2.sh
\n xpvm.sh )<\/p>\n
J) \/etc\/bash.rc – global shell<\/p>\n
a) umask – permission set
\n 1) root -0 – 0022
\n 2) above uid 99 (user) – 0022<\/p>\n
b) PS1 – define veriable (roota@localhost#). we can change ‘#’ to ‘$’
\n i.e. ‘root@localohost$’<\/p>\n
K) Users profile
\n a) \/root\/.bash_profile
\n b) \/root\/.bashrc
\n c) \/root\/.bash_history
\n d) \/root\/.bash_logout<\/p>\n
========================
\n END OF THE BOOT PROCESS.
\n ========================<\/p>\n","protected":false},"excerpt":{"rendered":"
*************** Summary =======<\/p>\n
A) START – BIOS (Basic Input Output System) = when BIOS load in RAM Called BOOT STARPPING – CMOS = Called this process KERNAL LANDING – MBR in Hard Disk – BOOTLOADER – KERNEL – INITRD IMAGE – Inittab = Upto this process called USER LANDING<\/p>\n
B) There are two tyeps of […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5],"tags":[],"_links":{"self":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/7084"}],"collection":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=7084"}],"version-history":[{"count":1,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/7084\/revisions"}],"predecessor-version":[{"id":7085,"href":"https:\/\/mohan.sg\/index.php?rest_route=\/wp\/v2\/posts\/7084\/revisions\/7085"}],"wp:attachment":[{"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=7084"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=7084"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/mohan.sg\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=7084"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}