Dennis,

> Run level 1 is basically the equivalent of Window "safe mode"

Thats what I remembered, hence the "very special mode".

> Remember init.d comes from System V UNIX, from a time
> before "single user computers".

:-) Thats not something I could have remembered I'm afraid.

>
https://www.2daygeek.com/sysvinit-vs-systemd-cheatsheet-systemctl-command-usage
/

Thanks.  It at least has a bit more descriptive names for those runlevels.
Still feel I have to guess a lot about what they are for though - Still have
no idea when to use those runlevels, or why (I'm a freshling, with
little-to-no knowledge about Linux or its history).

Ah, it seems that "S" and "1" (and "Single") are the same.  One thing less
to "worry" about.

> Sys-V init IS init.d.

Yeah, I totally knew that ofcourse. :p

> systemd processes it as an interim for upgrading systems

Is that "upgrading" ment as in the boot process, or should I take that as
meaning that raspbian itself is considered an in-between step to something
else ?

> When /entering/ run-level S, S01fake-hwclock will be invoked with
> the "start" parameter.
> When entering run-level 0, 1, or 6, K01fake-hwclock will be invoked
> with the "stop" parameter.

In short, when entering run-level 1 it will get started *and* stopped.
Which could make sense in fake-hwclock's case.

> I suspect the above comment block is used by update-rc.d program
> to populate the symlinks...

Currently I assume the same.   Makes me wonder why the source script needs
to be placed in the init.d folder though ...

> From man update-rc.d

Grumble ...   I tried "man init.d" and got nothing.  Didn't think to do the
same for update-rc.d though. :-\

> See the insserv(8) manual page for details about the LSB header format.

Bingo!   Or maybe not: "man insserv" -> "No manual entry for insserv" ?

> https://www.tldp.org/HOWTO/HighQuality-Apps-HOWTO/boot.html (see 9.3)

Hmmm ...  Chapter "9.2. Runlevels" shows a bit more detailed info about
those run-level numbers - and when they are supposed to be used. :-)

> pi@rpi3bplus-1:~$ ls  /etc/rc*.d

I think I should put a script specifying all the runlevels into system.d,
and see if I can syslog the crap outof it (assuming/hoping the run-level is
mentioned in the arguments).

> * X-servers are the hardware that renders the display, X-clients
> are programs that send display requests to the X-server. So --
> sort of backwards from how most client/server systems are viewed

That doesn't sound to odd to me to be honest, just a case of which
POV/perspective you (wish to) have.   I could argue that when I can execute
programs (on the mainframe) that I can leave and reconnect to at will than
I'm the controller, and they are the childs (even if I'm doing it on a dumb
terminal, with my actual OS also on the mainframe).

Thanks again.   Some of the info still goes a bit over my head, but overall
my "picture sharpness" improves. :-)

Regards,
Rudy Wieser

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