Understanding boot helps you troubleshoot startup failures.
Boot sequence:
. BIOS/UEFI: Hardware initialization, finds bootloader
. Bootloader (GRUB): Loads kernel into memory
. Kernel: Initializes hardware, mounts root filesystem
. Init system (systemd): Starts services
Systemd commands:
systemctl status nginx: Check service statussystemctl start/stop/restart nginx: Control servicesjournalctl -u nginx: View service logs
Interview question: "A service fails to start after reboot. How do you diagnose?" Check systemctl status, review journalctl, verify dependencies.