Need basics of booting process

[shariefbe]

Dear friends,

I want to know the basics linux booting process. I googled for this but i didn't find the detailed things anywhere. I want to know the boot process including the hardware work flow. Can anyone give me the detailed tutorial to learn about this.

Thank you

[theKbStockpiler]

I have not studied this for some time but I will give you an outline and some topics to search.


An O.S can not load its self into RAM therefore BIOS is needed. BIOS is a complicated ,emense topic and there is not a complete doc. on the web as far as i'm concerned. BIOS can be looked at as a O.S that is stored on a Chip and therefore can be considered as ROM unless it is reflashed. BIOS can run whether there is a O.S or a hard drive installed on the computer. Cmos is the type of Chip that BIOS is stored on.

Your going to have to study GRUB which is documented as bad as BIOS is.

Here are some links:

Powered by Google Docs


How Linux Boots

How Boot Loaders Work

http://en.wikipedia.org/wiki/Linux_s..._process:grin:

[Rubberman]

The "How Boot Loaders Work" is a decent basic explanation of what is going on in the boot process. I last wrote a PC boot loader about 25 years ago, but from what I remember, the information is correct. Bear in mind that EFI-enabled (Enhanced Firmware Interface) systems, such as Apple computers, work in a similar, but different, fashion. Basically, EFI is a more modern (32-bit capable) BIOS.

[Bemk]

Basically boils down to this:
CPU starts and loads BIOS from fixed point in memory and starts running. BIOS then reads the first 512 bytes or master boot (mbr) record and puts them at address 0x7C00, only to jump there (still in real mode).

Mbr is compiled to load the later stages of the bootloader (the first stage is installed in the mbr) and that basically sets up the basic configuration for the kernel and loads the kernel.

Kernel then completes setting up the CPU and starts the scheduler with the first task called init, which starts the programs needed by the runlevel.

Once that's done the boot scripts get their turn and once that's done, you're ready to log in. Everything from that moment on is obvious.

That's it in a nutshell.

Boot sequence - OSDev Wiki That wiki is very useful, especially during homework assignments regarding OS development and when writing your own kernel.

[lonewolff]

I am interested in this topic as well.

What are the files that contain the boot scripts (particularly Ubuntu).

Are they the same scripts between different distro's?

[Bemk]

Don't want to troll or anything, but I think you forgot the 9'th line of the forum etiquette .

But to answer the question anyway, look at /etc/grub.d for grub2, and for grub legacy: /boot/grub

[lonewolff]

I don't see how this was a hijack attempt, as it deals directly with the OP's question.

It seems that you have forgotten the 13th line of the forum etiquette.

Way to treat newcommers who are trying to take the time to learn Linux.

[Bemk]

I only tried to give friendly feedback, sorry if that was misinterpreted.

It did sound like the other user wanted to get more technical info instead of configuration.

So yet again, sorry if this was considered offensive, which was not at all my intention.

[lonewolff]

All good, your tips were pretty handy.

Sorry if I came across as a hijacker

Thanks again.