Linux Init Scripts
Beware, this model differs in important points from Solaris.
The normal /etc/rc?.d/* scripts are executed by /etc/init.d/rc (which is
invoked by init via /etc/inittab config).

/etc/rc.d is just a sym link to /etc/init.d.  Too bad /etc/init.d/ does
not just home init scripts like on Solaris :(.

This file does not describe how to "set up" and manage init scripts
("chkconfig", "insserv", etc.).
That is another level of complexity which is much simpler and is independent
from the runtime algorithms described here.


Every /etc/rc.d/rc?.d directory has all scripts that need to be run for
that level.  /etc/init.d/rc.d will compare to the "previous" level to
check whether S or K scripts may be skipped.  (For normal startup or
shutdown, we are going from a runnable level (2,3,5) to/from no level (N),
so all of the S or K levels from the runnable level will be executed.
This is the meaning of "previous" and "current" level reported by "runlevel".

REBOOTING
  On way DOWN, only the K scripts from current level are run + rc[06].d/S*.
      Levels 0 (halt) and 6 (reboot) have no K scripts, since the system is
      stopped after the S scripts run.  The only S script run at both of these
      is the "halt" script.
  On way UP, only /etc/init.d/boot is executed (directly by init, see inittab)
      + S scripts from new level.
    These execute /etc/rc.d/boot.d/*.

IDIOSYNCRACIES
    Docs and behavior are EXTREMELY AMBIGUOS re. runlevel S and 1.
    /etc/rc.d/README says that runlevel 1 is only for transitioning from a
    higher level to S.  If that is the case, then there is no need for K*
    scripts (for same reason that levels 0 and 6 have no K scripts).

    Runlevel S seems to be unstable on SuSE.  Can't exit from S without
    messages indicating state problems.  Runlevel 1 seems to be stable,
    but docs say it shouldn't be used (see previous paragraph), and it
    does too much for real trouble-shooting/recovery purposes (e.g.,
    loads all normal filesystems).

    /etc/rc.d/boot.d/K* seem to never run (rememeber that these are
    executed by /etc/init.d/boot, not by /etc/init.d/rc).


OFF-TOPIC
The "insserv" system really sucks.  The whole goal is to make init script
dependencies easy to manage and intuitive.  It fails those goals
completely and is extremely ambiguous.
Most critically, the definition, purpose, and correct usage of the
keywords isn't documented anywhere at all that I can find, and is completely
not covered by the "insserv" init script nor Suse's /etc/init.d/skeleton*,
or /etc/init.d/README.
What is the difference between "boot_facility" and "System Facilities"?
The "$..." facilities are pesueo-facilities.  The available pseudo-facilities
 are listed at /etc/init.d/skeleton.  The $ meaning here seems to have
 nothing in common with the $ directives in /etc/insserv.conf.
The man page says the "X-Start-Before" means that the service "should
be started before...".  What the hell is the difference between that
and ""Should-Start"?  If Should-Start means the service that this script
"should start", then how does that differ from "Provides"?
What is the behavior when a required service is not present?  The insserv
mentions talks about a "+" optional keyword in the context of "system
facilities", but doesn't say nearly enough to figure out how or where to
use it.

"service" just invokes init scripts with a clean environment.

insserv
use "insserv -d" to add init scripts instead of chkconfig.
chkconfig is just a wrapper and apparently emulates some more generally
known/available command than Suse's native 'insserv'.
    *-Start:
        Makes the earliest S scripts possible, while ensuring that
        Required-Start and Should-Start (if present) are started before.
        With no Stop-* directives at all, this will also make K* scripts
        as at LATE as possible, while ensuring that *-Starts are stopped
        after.
    *-Stop:
        Seems to have no effect at all on Suse systems.
        Does not work as documented in /etc/init.d/skeleton.