Whenever you're ready, walk me through how you'd approach this.
Describe the Linux boot process. Cover the path from firmware initialization through the bootloader, Linux kernel, initramfs, and the first userspace process. Explain where systemd fits, how the root filesystem becomes available, and how you would investigate a boot failure. Scope your answer to a typical modern x86_64 Linux system using UEFI and systemd, while noting important BIOS differences.