NOTES.init

NOTES.init -- read me file.  2011-04-23
$Id: NOTES.init,v 1.1.2.1 2011-05-10 13:45:29 brian Exp $
Copyright (c) 2008-2011  Monavacon Limited  <http://www.monavacon.com/>
Copyright (c) 2001-2008  OpenSS7 Corporation  <http://www.openss7.com/>
Copyright (c) 1997-2001  Brian Bidulock  <bidulock@openss7.org>
See the end for copying conditions (for this file).


Notes on init scripts:
======================

We used to place init script start and stop links in the 0-6 run levels.
Recently, however, the requirement to relink modules before loading in
support of weak-updating modules, the init scripts needed to run earlier
in the boot sequence.  There are, again, three basic approaches to
modern sysv init processes:

RedHat/CentOS/Fedora
--------------------

RHEL5 and earlier executes /etc/rc.d/rc.sysinit directly from the si::
entry in /etc/inittab.  It has no particular run-parts like boot
sequence.  System initialization under RHEL6 is done by upstart instead
of sysv-init scripts and run-level from /etc/inittab.  Nevertheless, it
still runs /etc/rc.d/rc.sysinit first and then starts the appropriate
run level from there just as the old inittab did.

However, rc.sysinit executes *.modules files found in the directory,
/etc/sysconfig/modules.  This is performed just after starting udev and
before mounting pts (pseudo-terminals) and applying system controls from
/etc/sysctl.conf.  This is a perfect place to execute our scripts, so se
place an openss7.modules in /etc/sysconfig/modules and have it execute
our scripts with the runlevel set to 'B'. (There is no runlevel in the
RedHat rc.sysinit at this point).

One problem is that local filesystems do not seem to be mounted at this
point and the root filesystem may still be read-only.

Therefore, normal 1235 init scripts must be used.

SuSE/OpenSuSE
-------------

SuSE used to use insserv for differential links, which it still does,
but now insserv is very LSB compliant.  Nevertheless, SuSE supports to
runlevel other than 0-6: B and S.  B is the system boot scripts that are
linked in /etc/init.d/boot.d.  S is the startup scripts for single-user
mode (scripts common to all runlevels 1 2 3 5) linked in
/etc/init.d/rcS.d and are not run until after all of the scripts in
/etc/init.d/boot.d.

SuSE runs parts in the /etc/init.d/boot.d directory directly from the
si:: entry in /etc/inittab by running /etc/init.d/boot.

We want to run our scripts after $local_fs but before boot.klog where
possible (because we want STREAMS up before syslog, but maybe the
STREAMS error and trace loggers after klog).

Note that scripts in /etc/init.d/boot.d will be run in parallel.

Scripts that are executable will be run with the 'start' argument;
however, scripts that are not executable will be run as a script under
/bin/sh with a 'b' argument encased with "Running $i" and the return
code displayed as success or failure.

Debian/Ubuntu
-------------

Debian used to use a fixed ordered process using the update-rc.d script
for installing and removing init scripts.  However, it now uses an LSB
compliant insserv utility (taken, it seems, from SuSE).  This is the LSB
prioritizing scheme with dependencies.

Debian/Ubuntu still uses a S runlevel, where system initialization
scripts are run.  Debian/Ubuntu runs parts in the /etc/rcS.d directory
directly from the si:: entry in /etc/inittab.

The 'runlevel' environment variable will be set to 'S' when scripts are
exectuted from rc 'S'.  The 'previous' environment variable will be set
to 'N'.  This is a clue that the script is being run at boot.

Debian/Ubuntu no longer treat scripts with a .sh extension differently
(sourcing them instead of executing them).  Note that Debian uses
/bin/dash as a /bin/sh replacement and no bashisms should be present in
the scripts.

Note that scripts in /etc/rcS.d will be run in parallel.

-----

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 Copyright (c) 2008-2011  Monavacon Limited  <http://www.monavacon.com/>
 Copyright (c) 2001-2008  OpenSS7 Corporation  <http://www.openss7.com/>
 Copyright (c) 1997-2001  Brian Bidulock  <bidulock@openss7.org>

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