Lesson 7 Dates: 3/5/2014

Start-up and Run Levels. Scheduled jobs (at, cron)

Linux for Engineering and IT Applications

Linux Bootup and Login Sequence 1. BIOS boot-ups; checks peripherals; finds bootable device. 2. First sector loaded into RAM and executed-- GRUB prompt appears. 3. Kernel loaded from sector list, /boot/vmlinuz-3.2.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/sda1. 7. Kernel executes Upstart /sbin/init as PID 1. 8. Ubuntu 12.04 LTS: Upstart init executes tasks in directory /etc/init, including rc-sysinit that starts the legacy scripts in /etc/rcS.d and the default run level, /etc/rcN.d. 9. The Legacy, System V /etc/init.d/rcS runs the scripts in directory /etc/rcS.d to set the console, clean screen, and so on; then /etc/init.d/rc executes all scripts for default run level, defined in /etc/inittab. 10. init spawns getty programs on each terminal. 11. getty prompts for login. 12. getty executes /bin/login to authentic user. 13. login requests a password and validates it against /etc/passwd, or NIS maps, or LDAP (depending on PAM settings). 14. login prints the message from /etc/motd. 15. login starts a shell. 16. The shell executes the appropriate startup files (.profile for sh, ksh; .bash_profile for BASH; .cshrc and .login for csh and tcsh). 17. The shell prints a prompt and waits for input.

Linux Bootup and Login Sequence Init is the parent process Exercise: pstree Upstart Exercises: start/stop services System Run Levels Changing the Run levels Booting into specified Run levels Startup Scripts Adding/removing scripts from startup Startup script example Exercises: VM setup for startup Exercises: run levels User settings at login Exercises Scheduled jobs: at Scheduled jobs: cron Exercises Take me to the Course Website