https://orig00.deviantart.net/60a0/f/20 … 3iiyfb.jpg

You really took it to the next level with the information about the pre-pivot start up. In my mind all that is simply "initramfs stage"--the fine details of which I never considered or even heard of before. Thank you very much for such an insightful answer.

The process is named udevd.

It's first started by its pre-pivot init-top/udev script, in initramfs. That process is then killed at the end of the pre-pivot init sequence, by its  init-bottom/udev script, still in initramfs.

Next it has its init link /etc/rcS.d/S0?eudev (or possibly /etc/rcS.d/S0?udev) for starting udevd in the post-pivot init sequence.

The pre-pivot start up includes a forced traversal of the /sys tree through a udevadm trigger --action=add command, and then that init-top/udev script also waits for udevadm settle to return, before it "pokes" extra on scsi devices, if any, followed by an optional additional timeout in some circumstances. Further, the init-bottom/udev script at the end of pre-pivot init merely kills the pre-pivot udevd process, and then moves the pre-pivot /dev to be available as post-pivot /dev.

Note that pre-pivot init is a script, usually a copy of /usr/share/initramfs-tools/init, and it ends with an exec run-init ..., which becomes the post-pivot init process (or a panic, if exec fails).

What starts the eudev service and how?