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Should tasks be considered harmful?




tl;dr: Desktop tasks have unexpected (from the user point of view) side
effects due to dependencies. This can be considered harmful since the
installer task selection can easily can trick a user into installing a
"substandard" system.

Yesterday I did something I rarely do: I installed Debian from scratch
on a laptop.  This is not something I do a lot, simply because there is
no reason with the excellent upgrade support Debian has. Even when I
occasionally change hardware, I usually migrate as much configuration as
possible - including the list of installed packages.

I must admit that I had very high expectations based on my previous
experience with Debian. I expected a smooth install ending up with a
system where everything just worked.  And it was close. But not quite.
And the failure was so unnecessary, and potentionally so difficult to
figure out for new users, that I think it is worth considering as a much
larger problem than a simple installation bug.

This old laptop had a built-in 3G modem (an Ericsson F3507g - not that
it matters), which I "knew" would work fine in Debian. Aleksander, Dan
and all the contributors have done a very nice job with ModemManager.
But the modem did not work. Because ModemManager wasn't installed at
all!  How did that happen?

I had briefly looked at desktop task choices during installation, and
not being too fond of any of the DEs, I arbitrarily selected LXDE.
Figured it couldn't hurt having a lightweight DE on an almost 10 year
old laptop.  What I missed completely was that the lxde package, which
obviously is a dependency of task-lxde-desktop, has this in its
recommends:

 wicd | network-manager-gnome

So it drags in wicd instead of network-manager-gnome.  Which I can
perfectly understand from a lightweight point of view.  But the problem
is that these two packages don't support the same features, and
'lightweight' isn't a good selection criteria during installation. In a
perfect world, the installer could have had sufficient information about
the hardware and the users wishes to make this choice. But it has
not. So it should install the options which are most likely to work for
all users.  Which is clearly network-manager in this case.  Replacing
wicd with network-manager-gnome, which drags in network-manager and
modemmanger, fixed my modem issue.

But how would a user without any previous knowledge of modemmanager or
Linux networking be able to figure this out? As a new user, would you
even dare to rip out the core network tool which was installed by
default, to replace it with something else?  I don't think so.  Many
users would be stuck with a non-working 3G modem and not being able to
fix it.  Which I find terribly sad, knowing the hard work put into
making ModemManager work as well as it does.

Now, of anyone is still reading, you are probably wondering why I didn't
just open a bug instead of writing this long story here. Well, AFAICS
there is no bug.

There is nothing wrong with the installer.  It just did what I asked it
to, since I selected this specific task.  I don't think it is reasonable
to expect the installer to do any dependency validation or overrides.
That would be crazy.  T

There is also nothing wrong with the task-lxde-desktop.  It depends of
lxde, which it obviously must do.

I don't think there is anything wrong with lxde either.  Recommending
wicd is fine with me.  It's just not suitable for everyone, and
therefore unsuitable as an installation default.  But that should not be
a concern for lxde.

And there is certainly nothing wrong with wicd.  It serves its purpose,
and does it well. A limited feature set is a perfectly valid design
choice.

So the installation end result is bad, but every package and subsystem
does exactly what they are supposed to do. It is the overall system
design that fails.  Which is why I think this is more of a policy
question than a bug.  Thinking on how I went wrong, I have come to the
conclusion that I would have been much better off if there were no
desktop task choice at all.  If I just got Gnome or whatever would be
the default.  Then I would also get the one and only "default set of
Debian packages", without any unexpected replacements.  I would of
course still be free to change the default desktop selection after
installation, as well as anything else.  But then I would have had a
much better opportunity to see the consequences, if dependencies caused
important system packages to be replaced.

IMHO the task selection during installation is harmful. Unpredictable
(from user point of view) results cannot be avoided, since any
additional package selected during installation will modify the resolved
set of dependencies.

I believe there was a similar problem related to automatic package
selection based on detected network environment during install.  This
has been resolved.  But the underlying issue is still there: If you
allow the installer to select or deselect *any* package during
installation, then it is very hard to predict how their dependencies
will modify the installation.




Bjørn