On Thu 19 Jul 2018 at 06:38:08 (-0500), Richard Owlett wrote: > On 07/18/2018 09:06 AM, Michael Stone wrote: > >On Wed, Jul 18, 2018 at 08:44:13AM -0500, Richard Owlett wrote: > >>First I'm looking comparison of required, important, standard, > >>optional, and extra as package labels [particularly interested > >>in corner cases]. I've been looking at > >>[https://www.debian.org/doc/debian-policy/]. I'm not grasping > >>something. Not sure what ;/ > > > >Well, it's hard to answer questions when you don't ask a question. > >For the most part the priorities don't matter much, and are > >largely a historical curiosity. Extra is gone, standard and > >important don't mean much. So most packages are optional, and a > >few that should be really hard to remove are required. Being > >required has the possible advantage that other packages don't need > >to explicitly list dependencies on the required package (but in > >practice you usually end up with a versioned libc6 dependency > >anyway). It does save a bit on the overhead of every single > >package having dependencies on /bin/sh and coreutils that the > >dependency resolver would then have to consider. > > > > I was, I thought, asking for explicit distinctions between adjacent > priorities. Your reply was that the distinctions were no longer > germane. That, effectively there are now only two, required and > optional. > > That changes the landscape surrounding a personal project. Which > some might describe as an extremely minimalist Debian. I would > rather describe it as a "proper subset" of Debian for a particular > use. That is why, in another thread, I ask about "Debian from > Scratch". > > That leads to asking two related questions: > 1. How can I get a list of packages tagged as required? > 2. What section of the installer installs packages tagged as required? > I assume the answer will, in part, be a referral to some developer > oriented documentation. [My motivation is personal education rather > that creating the next "killer app]. > > I will then investigate which of my optional packages already have > an explicit dependence on a "required" app. That will allow me to > enumerate which "required" packages *may* actually be unnecessary.
While there are commands like aptitude search and aptitude why available for such purposes, these are really designed for routine maintenance. For your purposes, I think you need to develop a more intimate relationship with the files in /var/lib/apt/lists/, particularly ftp.us.debian.org_debian_dists_stretch_main_binary-amd64_Packages (which may be named differently on your system). There's a similar file /var/lib/dpkg/status which contains a subset of this information for any packages with status on your system (usually "installed"). You can make many investigations (en masse) using OR'd grep expressions on these files, but for more in-depth investigations, it's worth parsing it into, say, a python dictionary of fields containing lists of items in each field. So, for example, I have a program which, for each package, gives a list of packages that Depends (± Recommends ± Suggests) on it. By filtering input to that program by the Priority of packages, and by Recommends/Suggests/¬Depends, it's trivial to answer your question about which packages are not required on your system, either through "Priority: required" or a Depends. Working on the raw data yourself might make it easier to study your corner cases that using the potted tools that most people suggest. Cheers, David.
