Manpages

Manpage of DEBCONF

DEBCONF

Section: Maintenance Commands (8)
Index
Return to Main Contents
 

NAME

debconf - Debian package configuration system  

DESCRIPTION

Debconf is a configuration system for Debian packages. There is no command named "debconf". Debconf provides a consistent interface for configuring packages, allowing you to choose from several user interface frontends. It supports preconfiguring packages before they are installed, which allows large installs and upgrades to ask you for all the necessary information up front, and then go do the work while you do something else. It lets you, if you're in a hurry, skip over less important questions and information while installing a package (and revisit it later).  

Preconfiguring packages

Debconf can configure packages before they are even installed onto your system. This is useful because it lets all the questions the packages are going to ask be asked at the beginning of an install, so the rest of the install can proceeed while you are away getting a cup of coffee. If you use apt (version 0.5 or above), and you have apt-utils installed, each package apt installs will be automatically preconfigured. This is controlled via /etc/apt/apt.conf.d/70debconf Sometimes you might want to preconfigure a package by hand, when you're not installing it with apt. You can use dpkg-preconfigure (8) to do that, just pass it the filenames of the packages you want to preconfigure. You will need apt-utils installed for that to work.  

Reconfiguring packages

Suppose you installed the package, and answered debconf's questions, but now that you've used it awhile, you realize you want to go back and change some of your answers. In the past, reinstalling a package was often the thing to do when you got in this situation, but when you reinstall the package, debconf seems to remember you have answered the questions, and doesn't ask them again (this is a feature). Luckily, debconf makes it easy to reconfigure any package that uses it. Suppose you want to reconfigure debconf itself. Just run, as root:
  dpkg-reconfigure debconf This will ask all the questions you saw when debconf was first installed. It may ask you other questions as well, since it asks even low priority questions that may have been skipped when the package was installed. You can use it on any other package that uses debconf, as well.  

Frontends

One of debconf's unique features is that the interface it presents to you is only one of many, that can be swapped in at will. There are many debconf frontends available:
dialog
The default frontend, this uses the whiptail (1) or dialog (1) programs to display questions to you. It works in text mode.
readline
The most traditional frontend, this looks quite similar to how Debian configuration always has been: a series of questions, printed out at the console using plain text, and prompts done using the readline library. It even supports tab completion. (Install the libterm-readline-gnu-perl package to make the most of the readline support.) This frontend has some special hotkeys. Pageup (or ctrl-u) will go back to the previous question (if that is supported by the package that is using debconf), and pagedown (or ctrl-v) will skip forward to the next question. This is the best frontend for remote admin work over a slow connection, or for those who are comfortable with unix.
noninteractive
This is the anti-frontend. It never interacts with you at all, and makes the default answers be used for all questions. It will occasionally mail root with messages the package wanted to display, but that's it; otherwise it is completly silent and unobtrusive, a perfect frontend for automatic installs.
gnome
This is a modern X GUI using the gtk and gnome libraries. Of course, it requires a valid DISPLAY to work; debconf will fall back to other frontends if it can't work. Note that this frontend requires you have the libgnome-perl package installed.
editor
This is for those fanatics who have to do everything in a text editor. It runs your editor on a file that looks something like a typical unix config file, and you edit the file to communicate with debconf. Debconf's author takes the fifth amendment regarding the circumstances that led to this frontend being written.
web
This frontend acts as a web server, that you connect to with your web browser, to browse the questions and answer them. It has a lot of promise, but is a little rough so far. When this frontend starts up, it will print out the location you should point your web browser to. You have to run the web browser on the same machine you are configuring, for security reasons. Do keep in mind that this is not a very secure frontend. Anyone who has access to the computer being configured can currently access the web server and configure things while this frontend is running. So this is more of a proof of concept than anything.
You can change the default frontend debconf uses by reconfiguring debconf. On the other hand, if you just want to change the frontend for a minute, you can set the DEBIAN_FRONTEND environment variable to the name of the frontend to use. For example:
  DEBIAN_FRONTEND=readline apt-get install slrn The dpkg-reconfigure (8) and dpkg-preconfigure (8) commands also let you pass --frontend= to them, followed by the frontend you want them to use. Note that not all frontends will work in all circumstances. If a frontend fails to start up for some reason, debconf will print out a message explaining why, and fall back to the next-most similar frontend.
 

Priorities

Another nice feature of debconf is that the questions it asks you are prioritized. If you don't want to be bothered about every little thing, you can set up debconf to only ask you the most important questions. On the other hand, if you are a control freak, you can make it show you all questions. Each question has a priority. In increasing order of importance:
low
Very trivial questions that have defaults that will work in the vast majority of cases.
medium
Normal questions that have reasonable defaults.
high
Questions that don't have a reasonable default.
critical
Questions that you really, really need to see (or else). Only questions with a priority equal to or greater than the priority you choose will be shown to you. You can set the priority value by reconfiguring debconf, or temporarily by passing --priority= followed by the value to the dpkg-reconfigure (8) and dpkg-preconfigure (8) commands, or by setting the DEBIAN_PRIORITY environment variable.
 

Backend Database

Debconf uses a rather flexible and potentially complicated backend database for storing data such as the answers to questions. The file /etc/debconf.conf is used to configure this database. If you need to set up something complicated, like make debconf read a remote database to get defaults, with local overrides, read the debconf.conf (5) man page for all the gory details. Generally, the backend database is located in /var/cache/debconf/  

Developing for Debconf

Package developers and others who want to develop packages that use debconf should read debconf-devel(8). Briefly, debconf communicates with maintainer scripts or other programs via standard input and output, using a simple line-oriented command language similar to that used by common internet protocols such as SMTP. Programs use this protocol to ask debconf to display questions to the user, and retrieve the user's answers. The questions themselves are defined in a separate file, called the "templates file", which has a format not unlike a debian control file. Debian packages which use debconf typically provide both a templates file and a "config" script (run to preconfigure the package) in the control metadata section of the package.  

ENVIRONMENT

DEBIAN_FRONTEND
Used to temporarily change the frontend debconf uses. See above.
DEBIAN_PRIORITY
Used to temporarily change the minimum priority of question debconf will display. See above.
DEBCONF_DEBUG
Turns on debugging output on standard error. May be set to a facility name or a regular expression which matches a facility name (such as '.*' to output all debug info). The facility names include:
user
Debugging info of interest to a debconf user.
developer
Debugging info of interest to a package developer.
db
Debugging info about the backend database.
DEBCONF_TERSE
Set to "yes" to enable terse mode, in which debconf frontends cut down on the verbage as much as possible.
 

BUGS

Probably quite a few, there's a lot of code here. If you do file a bug report, be sure to include the following information:
*
The debconf frontend you were using when the problem occurred
*
What you did to trigger the problem.
*
The full text of any error messages. If you can reproduce the bug, do so with DEBCONF_DEBUG='.*' set and include. This speeds up debugging a lot.
 

SEE ALSO

debconf.conf(5), dpkg-preconfigure(8), dpkg-reconfigure(8),  

AUTHOR

Joey Hess <joeyh@debian.org>


 

Index

NAME
DESCRIPTION
Preconfiguring packages
Reconfiguring packages
Frontends
Priorities
Backend Database
Developing for Debconf
ENVIRONMENT
BUGS
SEE ALSO
AUTHOR

This document was created by man2html, using the manual pages.
Time: 14:48:38 GMT, October 21, 2018