Lecture 4/3/2008

Linux (Debian) Bootup and Login Sequence
1. BIOS boot-ups; checks peripherals; finds bootable device.

2. First sector loaded into RAM and executed-- (LILO, GRUB, NT loader): prompt appears.

3. Kernel loaded from sector list, /boot/vmlinuz-2.6.x-xx; places the appropriate initial RAM disk image, initrd, into RAM.

4. Kernel executed; unpacks.

5. Kernel initializes hardware.

6. Kernel mounts root, /, file system, say /dev/hda1.

7. Kernel executes /sbin/init as PID 1.

8. init executes /etc/init.d/rcS script, which runs the scripts in directory /etc/rcS.d to set environment path, start swap, check the file systems, and so on; then init executes all scripts for default run level, defined in /etc/inittab.

9. init spawns getty programs on each terminal.

10. getty prompts for login.

11. getty executes /bin/login to authentic user.

12. login requests a password and validates it against /etc/passwd, or NIS maps, or LDAP (depending on PAM settings).

13. login prints the message from /etc/motd.

14. login starts a shell.

15. The shell executes the appropriate startup files (.profile for sh, ksh; .bash_profile for BASH; .cshrc and .login for csh and tcsh).

16. The shell prints a prompt and waits for input.

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