On Wed, 08 May 2024, Steve Litt wrote:

>
>I'm not familiar with /etc/rcS.
>

Typically, rcS.d are software or services that are started in addition of
whichever runlevel is selected. They're generally tasks that any runlevel
depends on, like mounting file systems, or enabling the network, or even
loading kernel modules.

-- 
Cheers,
                 Ludovic