Debian Sarge - Boot process

Debian's boot follows the usual steps:
- BIOS (Hardware low level initialization)
- Boot Loader (Grub or Lilo)
- Kernel loading
- Init start up and running services scripts.

Boot Loader
Debian Sarge (actual test version) uses Grub as default boot loader,
/boot/grub is the base directory where are placed various files:
- configuration file /boot/grub/menu.lst with options for boot action.
- file where devices (Ex. Hard-Disk, Floppy) are mapped:
- binary files of stage 1, stage 1.5 and stage 2 phase of grub.

All kernels images (vmlinuz-X-XX-XX) are placed in /boot with and initrd images, kernel modules are separated by kernel version in /lib/modules/.

Init startup stage uses the default configuration file /etc/inittab.
The first system initialization script launched is /etc/init.d/rcS, this runs all the scripts beginning with S in /etc/init.d/rcS.d/, after, init executes the services scripts in a directory specified by the default runlevel (/etc/rc?.d), where ? by default is 2.
Default run level organization follows:
Runlevel 0 is halt.
Runlevel 1 is single-user.
Runlevel 2 is multi user with text environment (in many other Linux distro, this corrispond to runlevel 3).
Runlevel 5 is multi user with graphical environment.
Runlevel 6 is reboot.
At runlevel S the system is in emergency mode, /etc/init.d/rcS is not executed and a sulogin is offered to the user.

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