README for sysv-rc
------------------

Policy requires that maintainer scripts use update-rc.d to register and
deregister initscripts.  An unfortunate result of this policy, combined
with shortcomings in current update-rc.d implementations, is that there
is no way for maintainer scripts to change the sequence number of an
initscript that has already been registered if and only if its sequence
number has not been changed by the administrator.  update-rc.d *never*
changes the sequence number of an already registered initscript, even
if its sequence number has not been changed by the administrator.
There are no plans to fix this problem.  Therefore, if it is necessary
to change the sequence number of an initscript in order to fix a bug
then the maintainer script should go ahead and do:

    update-rc.d -f <scriptname> remove

before the new update-rc.d call, even though this overrides out any
administrator changes.

Migrating to dependency-based boot sequencing
---------------------------------------------

Migrating to the dependency-based system of boot sequencing (using LSB
headers) is non-reversible, and renders obsolete the legacy system of
static sequence numbers. Please note that any boot sequence changes
made locally will be lost in the migration, and must be reimplemented
in terms of dependencies. However, the new system is recommended for
several reasons.

 * initscripts can be made to run more efficiently via parallelized
   execution strategies (see $POINTER_TO_ENTICING_BOOTCHARTS);
 * boot and shutdown ordering is calculated on the basis of the
   dependency information declared within each init.d script, ensuring
   that the sequence is optimized for the set of packages installed;
 * problems introduced by new or upgraded packages can be detected and
   averted - the boot sequence is only modified if it is safe to do
   so.

It can also bring benefits for Debian package development, and for
admins maintaining local software, since it eliminates the difficulty
of fitting an initscript into the boot sequence between existing
services with adjacent sequence numbers.

It is also a step in the direction of boot systems better suited to
the asynchronous nature of the Linux-2.6 kernel boot process.