Overall package list

[Jeff Hansen]

Hello,

I am trying to find an equivalent to Gentoo's /var/lib/portage/world in 
Ubuntu.  So far, it doesn't appear there is anything like it in anything 
but Gentoo, which is unfortunate.

Basically I want to get a list of packages installed on the system, but 
*only* packages that actually affect the installation of dependent 
packages.  For example, Ubuntu has the ubuntu-minimal, ubuntu-standard, 
and ubuntu-desktop "meta-packages" or virtual packages.  All you have to 
do is install one of these packages (I'll use ubuntu-minimal for the 
purposes of my question), and apt will automatically figure out all of 
the dependent packages to install from there.

After installing ubuntu-minimal, say I install the aptitude package.  It 
will install a whole bunch of dependent packages and then install 
aptitude.  At this point, the *only* two packages that really affect how 
my system is built are ubuntu-minimal and aptitude.  That's it.  I want 
a utility or option that will print out only these two package names.  I 
don't care about all of the other packages that were installed in order 
to get ubuntu-minimal and aptitude installed, I just want to know that 
ubuntu-minimal and aptitude are all I need to install in order to get my 
system to the same exact state I'm in now.

There is some code that should get close to this with "apt-get 
autoremove."  It looks like this does everything required to produce 
such a list, but it just figures out which packages have been orphaned, 
say, if I uninstall aptitude and all of those other packages are no 
longer necessary.  So, instead of removing orphaned packages, I just 
want to know which packages apt thinks are important to keep (i.e. 
usually only ones that I have manually installed, *not* dependency 
packages).

Hopefully someone on the list understands what I'm asking.  I'm pretty 
sure that Ubuntu does not have this feature, and maybe I'll have to 
write it if it doesn't.  Thanks.

-Jeff