Thanks to ¹ ² ³, today I learned about bootup(7) / `man bootup`⁴ ⁵ and boot(7) / `man boot`⁶ ⁷ ⁸ which document the early Linux system boot flow. Cool!!
¹: https://social.jvns.ca/@b0rk/114869060184792794 / 
@b0rkJulia Evans
²: https://toot.cat/@zeenix/114868965681011617 / 
@zeenixZeeshan Ali Khan 
🇺🇦
³: https://chaos.social/@lbky/114869069369093140 / @lbky
⁴: https://manpages.debian.org/bookworm/systemd/bootup.7.en.html (looks better in the terminal than in this HTML translation)
⁵: https://www.freedesktop.org/software/systemd/man/latest/bootup.html
⁶: https://manpages.debian.org/bookworm/manpages/boot.7.en.html
⁷: https://man7.org/linux/man-pages/man7/boot.7.html
⁸: https://www.kernel.org/doc/man-pages/ → https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/man/man7/boot.7