[Pkg-sysvinit-devel] Bug#806438: Bug#806438: update-rc.d: Do not fail when initscripts is not installed

[Petter Reinholdtsen]

[Felipe Sateler]
> On systemd systems, however, the ordering sequence is not used, and all
> that is required is that enable/disable links are present. So in systemd
> systems we can force insserv to generate the links even if the ordering
> is wrong.
>
> If a systemd-only system then installs initscripts, because initscripts
> calls update-rc.d in postinst, that will recompute the sequences, so the
> correct ordering should be reestablished afterwards.

While this approach seem like a sensible one, there is one failure mode
I would like to discuss first.

The scenario go like this.  On a system with systemd and no initscripts
package installed, several packages are installed and they work just
fine with systemd.  Then the system owner decide to switch away from
systemd to sysvinit and installs the initscripts package for this to
work.

But one or more of the already installed packages have a dependency bug
in their init.d scripts.  One of their required-start or required-stop
facilities are not available from any init.d scripts.  This will cause
insserv to refuse to install the initscripts package because of this.
The postinst fail when update-rc.d try to insert the new init.d scripts,
because it is impossible to order the current set of installed init.d
scripts.  It will become impossible to install new packages until the
initscripts package is purged, and the only way to fix it is to
installed fixed versions of all packages with broken init.d scripts (or
edit the problematic init.d scripts).

The way the update-rc.d script and insserv work today will ensure the
boot sequence is always consistent, and any new package breaking the
consistency will fail to install.  By adding -f to the insserv call,
this will no longer be true, and an broken boot dependency graph will be
allowed to exist, and only stop working when the -f is removed.

Is there a good way to avoid this?  Perhaps we could look at teaching
insserv how to handle multiple provides values, and list all the
initscripts facilities in a dummy script?  Or perhaps add some '-i
ignorefacility' option to insserv and ask it to ignore all initscripts
facilities when initscripts isn't installed?

-- 
Happy hacking
Petter Reinholdtsen