When automating server deployments with apt-get, interactive configuration prompts from packages like Postfix or MySQL can break unattended installation workflows. These prompts typically appear when packages contain debconf settings that require user input.

The Debian package management system uses debconf to handle package configuration. During installation, packages may:

• Present dialog boxes (text, graphical, or non-interactive)
• Store responses in a database
• Use these responses to generate configuration files

The most reliable approach is to set the environment variable:

export DEBIAN_FRONTEND=noninteractive

This forces all debconf interactions to use the noninteractive frontend, which automatically selects default answers.

For a complete unattended installation:

sudo DEBIAN_FRONTEND=noninteractive apt-get install -y postfix

In a script:

#!/bin/bash
export DEBIAN_FRONTEND=noninteractive
apt-get update
apt-get install -y postfix dovecot-core

For more control, you can preseed answers using debconf-set-selections:

echo "postfix postfix/mailname string yourdomain.com" | debconf-set-selections
echo "postfix postfix/main_mailer_type string 'Internet Site'" | debconf-set-selections

• Combine with -y flag for complete automation
• Works with apt (the newer alternative to apt-get)
• Affects all subsequent package operations in the same environment
• Doesn't affect packages that don't use debconf

If you still see prompts:

1. Verify the variable is set before running apt-get
2. Check if the package has mandatory configuration
3. Use dpkg-reconfigure after installation if needed

When automating server builds using apt-get, interactive post-install configuration dialogs can break the automation flow. Packages like Postfix, MySQL, or other services often prompt for configuration during installation, requiring manual intervention that defeats the purpose of scripting.

The most reliable way to skip these prompts is by setting the environment variable:

DEBIAN_FRONTEND=noninteractive apt-get install -y postfix

This approach works because:

• It tells Debian/Ubuntu's package system to use non-interactive mode
• The -y flag automatically answers "yes" to installation prompts
• Packages will use their default configurations instead of prompting

For more complex scenarios where you need to pre-answer specific configuration questions:

echo "postfix postfix/main_mailer_type select Internet Site" | debconf-set-selections
echo "postfix postfix/mailname string yourdomain.com" | debconf-set-selections
DEBIAN_FRONTEND=noninteractive apt-get install -y postfix

You can also configure this behavior through apt-get's configuration options:

apt-get -o Dpkg::Options::="--force-confdef" -o Dpkg::Options::="--force-confold" install -y package

These options tell dpkg to:

• --force-confdef: Use default configuration when available
• --force-confold: Keep old configuration files when they exist

After skipping the interactive configuration, you can deploy your custom configurations:

# Example for Postfix
DEBIAN_FRONTEND=noninteractive apt-get install -y postfix
cp /path/to/your/main.cf /etc/postfix/main.cf
systemctl restart postfix

Remember that:

• Some packages may require minimal configuration to function properly
• Always test your automated installations thoroughly
• Document which packages require special handling
• Consider using configuration management tools (Ansible, Puppet) for complex setups