Comment 1 for bug 10556

The fstab-generating code is not a single block that can be moved around easily;
it's part of the modular partition manager, and it requires the parted server to
be running. At the moment it isn't possible to run it during base installation,
because the parted server will not be running so it won't be able to get
partition details.

In order to fix this, I think we'd have to run fstab.d to write to a temporary
location and then figure out how to move bits of partman-target (at least
finish.d) out to somewhere else where they can be run separately independently
of the parted server. I agree that it might well be useful to do something like
this so that it's easier to skip partman and get a sane result at the end. The
complexity of the change puts it firmly in the "enhancement" category, though. :-)