Using Debconf

Debconf is Debian’s configuration management system. It stores user inputs and configuration options for packages during installation, upgrade, and removal.

Structure of the templates File

A templates file consists of multiple template entries, each defining a specific question. Each entry follows this format:

debian/templates
1 2 3 4	`Template: mypackage/question_name Type: string Default: default_value Description: A brief explanation of what the user should enter.`

Field	Description
Template	Unique identifier for the question (mypackage/question_name).
Type	The type of input expected (see below for options).
Default	The default answer if the user does not provide one.
Description	The message displayed to the user.

Types

string: User enters a free-text string.
boolean: Yes/No question.
select: User selects from predefined options.
multiselect: User selects multiple options.
note: Displays a message but does not ask a question.
password: Hides user input for security.

Boolean (Yes/No)
1 2 3 4	`Template: mypackage/enable_feature Type: boolean Default: true Description: Do you want to enable this feature?`

Select (Multiple Choices)
1 2 3 4 5	`Template: mypackage/choose_option Type: select Choices: Option1, Option2, Option3 Default: Option1 Description: Please choose an option.`

Multiselect (Multiple Selections)
1 2 3 4 5	`Template: mypackage/multiple_choices Type: multiselect Choices: Red, Green, Blue Default: Red, Blue Description: Select colors (use spacebar to select multiple).`

Note (Just a Message, No Input)
1 2 3	`Template: mypackage/info_message Type: note Description: This package will install additional dependencies.`

Read the User's Input in postinst

Once the user enters values during installation, you can retrieve them in debian/postinst:

postinst
#!/bin/bash
set -e
. /usr/share/debconf/confmodule

db_input high mypackage/config_value || true
db_go

db_get mypackage/config_value
echo "User entered: $RET" > /etc/mypackage/config.txt

Tells Debconf to show a prompt for mypackage/config_value. high is the priority (other options: low, medium, critical). || true ensures the script does not fail if db_input encounters an issue.

Displays all pending Debconf questions in one go. Must be called after db_input to show the prompt to the user.

Retrieves the user's input from Debconf. Stores the value in the $RET variable.

postrm

postrm
#!/bin/sh
set -e  # Exit on any error

# Example: Remove the config directory on purge
if [ "$1" = "purge" ]; then
    echo "Configuration directory removed."
    echo "PURGE" | debconf-communicate my-python-app || true
fi


exit 0

other debconf commands

Debugging and Testing

To check stored values:

1	`sudo debconf-show mypackage`

To manually set a value:

1	`echo "mypackage/config_value mypackage/config_value string new_value" \| sudo debconf-set-selections`

To reset and ask the questions again:

1	`sudo dpkg-reconfigure mypackage`

package script file location

ls -l /var/lib/dpkg/info/mypackage.*
#
This will show various control files for the package, including:

/var/lib/dpkg/info/mypackage.postrm → The post-remove script
/var/lib/dpkg/info/mypackage.postinst → The post-install script
/var/lib/dpkg/info/mypackage.prerm → The pre-remove script
/var/lib/dpkg/info/mypackage.list → The list of installed files