The script does not "exist". That means when I do
sudo service rc-local stop
it stops, and when I do
sudo service rc-local start
it is then hanging, or running, it is fine, but I
would like to exit back to shell on such run.
Adding & on end of line is not helping.
How do I make it execute and exit back to shell?
You don't, if you want it supervised. If you want to launch s6-svscan
under systemd, you should write a proper unit file for it, so systemd
can manage it as one of its services.
If you're fine with it not being supervised and insist on launching
s6-svscanboot from /etc/rc.local, then you want to enclose all its
commands in a "background { }" block, which is execline's equivalent
of the shell's &.
--
Laurent