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Faster shutdown and the ubuntu "multiuser" update-rc.d extention

Did you ever curse that Debian took so long to shut down, waiting for
all the shutdown scripts to complete before the machine was ready to
move?  Here is a simple recipe to help making sure your package do not
slow down the shutdown.

Most of the init.d scripts are simple scripts that during shutdown
kill the process they started during boot.  But the default halt (0)
and reboot (6) shutdown sequences will kill all processes on their own
(in the sendsigs script), so there is normally no need for individual
packages and init.d scripts to run at shutdown if all they need to do
is to kill a daemon.  There might be exceptions, for example if the
daemons need to stop in a given order, but that do not seem to be the
case for most packages.

Ubuntu discovered this a while back, and introduced a method to avoid
calling stop scripts in runlevel 0 and 6.  It is the "multiuser"
extension to update-rc.d, and in Ubuntu packages are changed to calls
dh_installinit with '-- multiuser' as an argument to enable it.  This
add the "multiuser" argument (instead of to the "default" argument) to
update-rc.d, which go on and set up the boot sequence without
references to the script in runlevel 0 and 6.  This can be done
without such extention, and how is the topic of the rest of my email.

To change the runlevel settings of an init.d script using the Debian
API, one most first remove it in the postinst, and insert it again.
To do this, add code like this in the postinst before the #DEBHELPER#

  if dpkg --compare-versions "$2" lt "0.1"; then
      update-rc.d -f hotkey-setup remove

The version number used when comparing should be the version of the
package where the change is introduced.

Next, change the dh_installinit call in debian/rules file to look like
this (note, not the optimal solution):

  dh_installinit -- start 20 2 3 4 5 . stop 20 1 .

This is equivalent to the 'dh_installinit -- multiuser' call on
Ubuntu, and will make debhelper add code to call update-rc.d with the
given arguments.

It is a long-standing Bug in the Debian single user and shutdown
sequence that the services are not stopped in the opposite order of
the one used when starting them.  The default setting is to start at
sequence number 20, and stop also using sequence number 20.  A better
default would have been to use a stop sequence number that is 100
minus the start sequence number, but it is too late to change the
behavior of update-rc.d.  Each package maintainer can on the other
hand fix his package like this:

  dh_installinit -- start 20 2 3 4 5 . stop 80 1 .

Of course, one need to verify that the stop script will still work
when stopped at sequence number 80 in the single user runlevel, before
introducing such change.

And while you work on your init.d scripts, please make sure to update
the LSB-style header Should-Stop to reflect that the script do not
need to stop in runlevels 0 and 6.  See
<URL: http://wiki.debian.org/LSBInitScripts/DependencyBasedBoot > for
more info on this feature.

Happy hacking,
Petter Reinholdtsen
One of the sysvinit maintainers

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