The BIOS loads and execute the first 512 bytes off the disk
(/dev/hda), a.k.a. the Master Boot Record (MBR)
The boot loader executes the first 512 bytes of the partition that
you selected (if more than one is available).
Advanced boot loaders like Grub or System Commander offer more features
than the DOS boot loader. Some boot loaders save their configuration in
the MBR (hence the need to remember to run the lilo command after
editing it to save your changes to the master boot record on disk), while others
save their data in a partition
The partition loader now decompresses the kernel in RAM, and runs it
The kernel initialises devices, loads the root partition,
loads the /sbin/init process (PID=1) that reads its configuration
information from /etc/inittab to know which boot scripts to run
and at which run-level to start, and which processes to spawn.
The actual scripts are in /etc/rc.d/init.d, and /etc/rc.d/rc#.d
only contains links
Init launches Getty to open consoles, and launches Login
to present the user with a logon prompt
Note that once the Linux kernel has been loaded by lilo,
it looks in "all the usual places" for init and runs the first copy it finds.
More information: Inside the Linux boot process by Tim Jones
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