Linux initrd boot scheme (initramfs-tools)
After initrd image unpack and mount to / (rootfs, tmpfs):
mount /sys and /proc
init-top hook
init-premount hook
local-top hook
local-premount hook
mount realroot to /root
local-bottom hook
init-bottom hook
move mount /sys to /root/sys
move mount /proc to /root/proc
exec run-init(klibc)
delete rootfs contents
overmount from /root to /
chroot and chdir("/")
exec /sbin/init