What is the detail boot process in linux? Start form Pc
on..?
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Answer / guest
Once system powered on, first thing will be POST check i.e
power on self test.
Then BIOS loads the MBR from the disk into RAM. Then, the
BIOS executes the MBR code. now boot loader list the number
of OS installed in to the system. select the OS wants to be
boot once OS selected initial RAM disk (temporary root file
system) are loaded into memory. When the images are loaded,
the boot loader passes control to the kernel image and the
kernel is decompressed and initialized.At this stage, the
boot loader checks the system hardware, enumerates the
attached hardware devices, mounts the root device, and then
loads the necessary kernel modules. When complete, the first
user-space program (init /sbin/init) starts, which will
looks file /etc/inittab to find the which runlevel kernel
will be boot then it will be check /etc/rc?.d (? means
runlevel got from inittab file)and check every script which
starts with name S will start in to that level once
completed, initrd(temporary root file system) will be
unmounted and mount the physical filesystem and loads the
main kernel then login prompt will be available.
Then
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Answer / frankie
I would like to add a few more points to the above answer:
When a system is powered on, first is the POST i.e Power on self test. BIOS loads the MBR from the disk into RAM. Here MBR is of 512 bytes, out of which 446 bytes has detail about bootloader information, 64 bytes has info about operating systems in the hard disk, 2 bytes has info about partition in the hard disk.
Further the bootloader is of 2 stages, 1st stage bootloader and 2nd stage bootloader. 1st stage initiates the 2nd stage bootloader and 2nd stage points to the sector of the operating system chosen from the bootloader list. Then the image file is loaded to RAM and goes further. ( Pls refer to the above answer after this)
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Answer / vipin kumar
first start from the power on .
1-processor start and tranfer the control to bios
basic i/p output function ,it will perform the post test
post is power on self test .it check all the hardware attached
with the help of id keyoboard id is 1.so it will first check
keyboard first.
2-then bios load into the memory whatever program is
residing in the first sector of the mbr.
mbr is 512 bytes in size.(master boot record)
mbr then load the first stage of bootloader its all job to
load 2nd stage bootloader into the memory.
3-when 2nd stage bootloader will load into the memory you
will see a red screen where you will see operating system
entry like redhat server rhel5.4 and other os like others.
4-2nd stage bootloader will determine which kernal is to
load ,then it will load corresponding kernal binary into the
memory.
kernal will load the initial ram disk image into the memory
called initrd in to the memory.
initrd load the basic driver to start the os.
once initrd load it transfer the control to the kernal .
5- when kernal load into the memory it configure all
hardware attached to it. and in order to setup user
environment it start init program.
6-init is the first program and it is also called the parent
of all the program .
it start /etc/rc.d/rc.sysinit to set the user environment.
start swap and check file system.
this is the last stage.
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