RHEL7 Boot Process Step by Step Explained – Tech Arkit

RHEL7 Boot Process Step by Step Explained – Tech Arkit


Hi friends welcome to Tech Arkit YouTube channel
my name is Ravi in this video session we are going to see that RHEL7 boot process, whenever
you switch on your machine so what happenes here it is that the machine will be boot up and
you can see that various process to boot up your machine and all this process what happens
when your switched on your machine are the power-on you machine whats goes on so let’s see that okay.! if I say first of all if you click on a power button on your machine examples say that
if you take a physical machine of your machine machine in the sense your
computer, whenever you press power button on your machine what happens so what happens here it is that switch on power supply so power supply in the sense it’s do a SMPS power-on which means that the switch mode power supply will be on whenever you switch-on then it verify the post post in the sense power on self test so each component of your hardware the computer hardware will do their own self test that whether I am able to power of myself then what happens to a power self test each
component in the sense all these RAM processor and the north bridge, south bridge is all the stuff
will be do their own self test then what happens if the self test is passed, then you will get a
one beep, if it is an design with the name sound in the sense you connect a speaker it says
kik then your system will be switched on then immediately there is a program called BIOS will be loaded BIOS in the sense basic input output system so the system will
load your BIOS firmware are the hardware related information all the hardware related information
and boot process like how you are boot device order be in the sense like the first order of the hardware devices if you have multiple drives connected in your system example say that you have connected CD-ROM DVD-ROM and you have connected removable media (Pendrive) and you have connected hard drive and
you have connected any external hardware to the machine then which boot order I should select In the sense I have to look of first CD-ROM? or i have to look up for network card I have to look for local hard drive I have to look for something else so then this basic input
output system will guide you through the settings whenever you said that system okay you just boot up with the local hard drive so don’t go anywhere then it identify that hardware
and okay what ever the local hardware where your operating system has been installed then it find out that drive and it goes to that then whenever your hardware whatever you are hard drive loaded in the since hardware found then immediately whenever your hardware is connected
and its look for the first boot record which means that the MBR so Master boot record where
in the hardware to the first sector of the hard drive itself the MBR will be
located so whenever the MBR is reading so what happens it find out that ok here is my MBR so the MBR size which is in 512 bytes which means that 512 bytes that bytes what happens
so whenever you are that bytes the boot information will be loaded the boot record is loaded in
the boot record it identifies the information so the information is like this example say
that if you can take example over here if you take example over here so example see this
so not this one example actually is an actual stuff ok let’s take any other ok example say that this is your 512 bytes of information so the MBR one okay bye then in this bytes so what happens here is is that so there is the information of your bootloader and about your
partition information example say that this one the first one would be a 446 bytes and 2nd 1 would be 64bytes and third one would be two bytes so what does mean by this 446 and 64 and 2 bytes 446 bytes will have this information of your stage one which include
all your information about you are the boot image where the boot images located and
all the information about the boot image okay so the image where it is located actually
so that information would be located over here and in the 64 bit of this information will
be located like the partition table information like in system how many partitions I have
at which partition is located from which sector to which sector that sector details and the inode information would be available here and the partition information and The mount point Information of be available over here ok so whenever you say that the boot load information available over here OK then what happens then the bootloader of information tell
to the MBR that ok this is your bootloader information here is your boot loader go ahead then after that you can find out that ok here is your partition information of the these are the partitions you have in your system are these are the partitions are compulsory to
be loaded on the boot itself then these two numbers is magic numbers which will verify the errors which means that magic bytes will identify the errors if any If in case you
check the partition to be verify the errors of the boot then what happens here is that the partitions will be verified with and each and every black will be verified of that on
this partition should be verified and say that ok there is no error, then you can go
ahead and if there any error it says that ok do you want to fix itself then you can
fix there itself by typing e2fsck -f based on the file system types OK then
it goes to the next level so MBR says that MBR it find out the master boot Record
Information then what happened it goes to the next level next level called a GRUB means grand united sorry Grand Unified loader so what this will do so this will do
in stages information also in this GRUB it load into the three stages the stage 1 stage
1.5 and stage 2 so in this three stages what it will do here it is the it will find out
this byte of stage 1 where this image is located and the next one is that INITRAMFS details where it is actually the compressed kernel is located on information
in the stage 1.5 and the core image and the grub2 Kernel located information will be
located on the stage 2 so what in this stage 2 it will find out where actually my
boot image is and where is my core image is and where is my RAM image is else Initial RAM (initramfs) information where it is located using sincerely it loads a files are the kernel boot it extracted
kernel information into the RAM file system ok so in the GRUB it’s do in
a three stages which is called 1, 1.5 and 2 stages then after that the compressed
kernel will be extracted into the initial file system as a read-only which is called /sysroot read only /sysroot mount point read-only file system whenever it’s
find out all the related information on that find out the kernel located information there and the kernel menu information on there then what happened it immediately load into the The Kernel boot where they will give that the first screen in the virtual machine are
the in the system VMware here maybe ok I just go over here say that please start
this machine so if I restart this machine say that’s ok restarting over here so this
is where your Kernel information is loaded this is your Kernel so if I say that
an example over here if I want edit this kernel information over here so this is where your kernel information will be stopped ok so this is your kernel information the Kernel VMLinuz information and this
all information will be located here see this this Initramfs image and all will be located over here OK then what happens if we load into them and say that
ok my compressed kannal information will be extracted and Little Mount is a / root read
only file system then whenever it is uncompressed has been completed extracted then it is jump
into the next stage called the system to system so this is your initial system when ever your
system d is starting so what happens if it is the the initial wherever you are enabled
all the processes and related stuff is going to start over here ok before that nothing
is started it that’s just the kernel is extracted in the calories just running other Canal is
been loaded all this case Canal models all the stuff then it going to the system d so
where the system is going to start this is the initial processes the system date self
start with the photo call the system for column will start the system the process it’s the
system the process will be a father of are there in the mother of all the processes will
be controlled by system the solar system they will be started using this the system for
call OK then the system the process will be started with the the process ID called one
then next process will be going to start so the next process is going to be start where
so here we set a target target Innocence so which target utilised to boot into example
say that you wanted to boot into the multi is a target are you wanted to boot into the
guitar guitar you wanted to boot into the sea light I get something like that so what
you said to the machine are the default target that will be loaded so what are the target
will be assigned to the default in the target how many services has enabled more between
the services are unable to start in the startup itself so the target will be loaded where
your services will be start ok so your service is going to be start then what happened your
services or services one by one it’s going to be start so the services like examples
that I have enabled the any process Mein bsss process is CPU processor and what are the
processes are you have enabled on that target will be loaded and it’s going to be all the
process will be started one by one ok ok ok then then it’s going to be a user interface
so where you said a user interface as a c l i n is going to into the sea lie you set
your target as a g u i then it’s going to be load your system so if you say that ok
My target is too busy you are then you are into this user interface where you will get
to ask or it is it will ask you for username and password detail example say then you just
whenever you enter your username and password then its enter into your machine this is half
the process is going to be happen beyond seen like whenever you press the power button then
it’s going to be do when an SMPS like this possible I will be on then after that the
all the components which going to be on a shelf tested then it’s going to be run a basic
input output system called by then after that the Empire the master boot record will be
identified in that master boot record where the birth of the bootloader and partition
information and the checking will be is going to be happen next the next to that the graph
is going to be loaded ok in that are going to be identified that all this boot image
Kaur image and all the initial Ram the initial length Ram affairs will be identified the
images will be identified and the canal will be loaded in that Canal the compressed can
only be extracted into 13 and then its mounted as a read-only file system then after that
the control is going to be controlled by the system the process the system the process
will be started by the system for call in the system for call me at system the fast
in the system they will be identified with the process ID number one because the process
ID sleep yet assigned in the random We Are The Secret Silverlight Round Robin mechanism
12345 something like that it’s going to be ultimately the first process that’s why it
will going to be get the process ID called war after that he will take the all the control
of your system then the system will be put into the default target water that reduces
then then what are the target is enabled the services or services will be loaded on the
target itself then or services will come of one by one the next is going to be any user
authentication where was you provide the user authentication details then you are system
Will Be Loved in into the user interface what are the user interface you said as a loading
example that you sent us Airlines going to the sea life is a disease UAE going to be
a graphical user interface that you are going to be complete then you are you are going
to get the you can walk on the other pl7 you can do whatever you want social networking