Part 6 · 1 chapters · ~8 min

Booting

Firmware (BIOS, UEFI, iBoot), secure boot and the chain of trust, bootloaders, the kernel command line, initramfs, PID 1 and systemd units, boot-time analysis, and what changes for containers and microVMs that boot in milliseconds.

Power-on to PID 1

code

dmesg | head -50                 # kernel messages from early boot
cat /proc/cmdline                # how the bootloader configured the kernel
systemctl list-dependencies multi-user.target | head
systemd-analyze blame | head     # slowest units at boot

FROM POWER BUTTON TO LOGIN

each stage loads the next, more capable one

swipe the figure sideways, or tap expand for full screen

1/5

firmware

Power-on runs firmware from ROM (UEFI on PCs, iBoot on Apple Silicon): it checks hardware and finds a bootloader, verifying signatures when secure boot is on.

firmware finds and verifies a bootloadersecure boot starts the chain of trust