Topic 10

Dates: 6/19/2019
Start-up and Run Levels. Scheduled jobs (at, cron)
Linux System Administration

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-4.15.0-xx-generic; 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 init (Systemd) as PID 1.

8. Systemd initiates the units in the default target. The units start the services.

9. Among the started services, there are agetty programs on each terminal and the login process.

10. login requests user name and password and validates them against /etc/passwd, or NIS maps, or LDAP (depending on PAM settings).

11. login starts a shell.

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

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

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