BOOTSTRAPPING IN LINUX

Bootstrapping

Bootstrapping done in following two phase.

1)   Kernel Loading

i)        Once GRUB has started and you have selected Linux as the operating system to boot, the first thing to get loaded is the kernel.

ii)      No operating system exists in memory at this point, and PCs (by their unfortunate design) have no easy way to access all of their memory.

iii)    Thus, the kernel must load completely into the first megabyte of available random access memory (RAM), In order to accomplish this, the kernel is compressed.

iv)    The head of the file contains the code necessary to bring the CPU into protected mode (thereby removing the memory restriction) and decompress the remainder of the kernel.

2)   Kernel Execution

i)        With the kernel in memory, it can begin execution, It knows only whatever functionality is built into it, which means any parts of the kernel compiled as modules are useless at this point.

ii)      At the very minimum, the kernel must have enough code to set up its virtual memory subsystem and root file system (usually, the ext3 file system).

iii)    Once the kernel has started, a hardware probe determines what device drivers should be initialized.

iv)    From here, the kernel can mount the root file system, root system is same as that of C drive in windows OS.

The kernel mounts the root file system and starts a program called init.