Com Sci 501
System Administration in Linux

Department of Computer Science
The University of Chicago

Installing and Upgrading Debian Packages with Dselect

Dselect is a program with a menu-based user interface for installing and upgrading Debian packages. Read the Dselect Tutorial for more systematic information. I'll give some tips that may help you get through important project tasks, before you get really familiar with Dselect.

The value of Dselect

The user interface for selecting software packages in Dselect is undeniably very annoying. I still recommend that you use it, because the benefits after you have made your selection are substantial. Dselect keeps a database of your software choices, which it co-ordinates with the database kept by the Debian package-maintenance system, dpkg. Once you have set up your choices, Dselect will upgrade automatically over the network, whenever one of your chosen packages changes. So, you get free system administration support from the Debian team of package maintainers. Notice that the key issues here are more social than technical. It is the willingness of the Debian team to do this service, and the good quality of their work, that make Dselect valuable, much more than the functionality of Dselect itself.

Progressing with Dselect

• The first time you use Dselect should be when the Debian installation tool starts it automatically. Follow my instructions at the the end of Install Debian GNU/Linux.
• The next few times you use Dselect, continue to ``[A]ccess'' packages from CD-ROM. Just skip the 0. [A]ccess menu item to leave this as it was, skip also the 1. [U]pdate item, and go right on to 2. [S]elect.
  • You see a screenfull of help information, probably too much to assimilate right now. Exit by typing [Space].
  • You see a rather cryptic screen presenting part of the list of Debian packages available to you. Capital ``O'' and small ``o'' change the order of the display in peculiar ways. Type ``OOo'' so that the first line reads ``dselect - main package listing (by section)''. The ``(by section)'' ordering groups packages by the type of services they provide.
  • You may navigate the list of packages fairly intuitively, using the arrow keys, [Page Down], and [Page Up]. Each line in the display corresponds to a package, one of which is highlighted in grey. Another line toward the middle, highlighted in blue, describes the status of that package fairly cryptically. A sequence of 4 characters to the left of each package line describes the status even more cryptically. A short text in the bottom half describes the services provided by the package.
  • Learn to read the highly cryptic character sequences. The first, which is usually blank, indicates whether an error has been encountered trying to install this package. The next, usually ``*'' or ``_'', indicates whether the package is already installed. The next two indicate your choices: a previous choice, followed by your current choice. The ``*'' indicates installation, the ``_'' indicates no installation, and the ``-'' indicates purging. Hitting ``v'' toggles between this type of display, and a more verbose one. The verbose display is impossible to read over a long period of time, but it helps you get the idea of the short one. Toggle back and forth a few times, until you have a pretty good idea how to read the 4 cryptic characters.
  • When you know the name of the package you want, type /<name> to search for it. This is the same way that you enter a search string in more and less, but you'll see that it operates a bit differently.
  • When you have the package of interest highlighted in grey, type ``+'' to select it for installation (and occasionally, ``-'' to select it for purging). Notice the immediate change in the rightmost character of the cryptic status code on the left.
  • Dselect checks immediately for inconsistencies, called conflicts or dependency problems, introduced by your new choice. If there are any conflicts, you will drop immediately into a conflict resolution display, showing a proposed set of changes to resolve the conflicts.
    • At any time during conflict resolution, if it's just too spooky and you're afraid it's leading all the wrong way, just type capital ``X'' to cancel the whole idea.
    • The scariest inconsistencies are the conflicts, in which two packages are incompatible with one another. The attempt to install a new package may require you to purge an old one. Make sure that you don't mind giving up the old one. Sometimes, the new one includes the old one plus more, but sometimes each has advantages and disadvantages. Hit ``X'' if you're not sure, and think about it some more.
    • Dependencies are great. If you choose a package that requires others, Dselect makes it very easy to grab them all. If all of the ``problems'' are dependencies, you usually want to accept Dselect's proposed resolution, which you may do by typing [Enter].
    • Occasionally, there is a dependency that allows a choice. In such a case, Dselect appears to make an arbitrary choice, but it will show you the alternatives. Packages may also ``recommend'' or ``suggest'' other packages without depending on them. In this case, it's really up to you.
    • You may select packages for installation and purging with ``+'' and ``-'', just as you do in the main listing.
    • In a few cases, there are errors in the packages, making it impossible to resolve the conlicts or dependency problems. All of the cases that I have noticed have involved changes of names that some package maintainers failed to notice. None of them have involved important packages. There are ways to over-ride the Dselect restrictions when you are sure you want to, but you can learn those from the manual.
  • When you are satisfied with your selections, type [Enter] to return to the main menu.
• 3. [I]nstall requires little interaction. With CD-ROM access, this step checks every package on the CD, so it's a good time to grab some tea. But, occasionally the installation process asks you some questions, and it may be important to answer correctly. In particular, it often offers to rewrite configuration files for you. In this case, you should always suspend Dselect, and check in any old version of the configuration files with RCS (we'll discuss this elsewhere).
• 4. [C]onfigure almost never does anything.
• 5. [R]emove usually does nothing, but what it does may be dangerous. Think back whether you accepted some conflict resolution too carelessly. Keep in mind that the whole package system itself, and many crucial system functions, are in packages. Watch this step, and cancel it with [CTL]-c if it looks fishy.
• You can figure out 6. [Q]uit.
• Later, when you have mined the CD rather thoroughly, you will switch to FTP access. Then, you will run the [I]nstall step of Dselect from time to time, even though you haven't selected any new packages. Dselect will automatically install any upgrades to packages that you selected before. Special instructions may come out from time to time for using Dselect to make major system upgrades. We will look more carefully at updating packages through FTP later.