When automating server provisioning with bash scripts, running sudo ufw enable presents a common obstacle - the interactive prompt asking for confirmation. This breaks the automation flow and requires manual intervention.

UFW (Uncomplicated Firewall) is designed with safety in mind. The confirmation prompt appears because enabling the firewall could potentially lock you out of the system if not configured properly first.

The standard output looks like:

Command may disrupt existing ssh connections. Proceed with operation (y|n)?

Method 1: Using yes Command

The simplest solution is to pipe the output of yes command:

yes | sudo ufw enable

Method 2: Using printf

For more control, use printf to send exactly what you need:

printf 'y\\n' | sudo ufw enable

Method 3: Expect Script

For complex interactive prompts, use expect:

#!/usr/bin/expect
spawn sudo ufw enable
expect "Proceed with operation"
send "y\\r"
expect eof

Method 4: UFW Non-Interactive Mode

Some versions support a non-interactive flag:

sudo ufw --force enable

Here's a full bash script example for setting up UFW rules automatically:

#!/bin/bash

# Allow SSH first to prevent lockout
sudo ufw allow 22/tcp

# Auto-confirm the enable command
printf 'y\\n' | sudo ufw enable

# Add additional rules
sudo ufw allow 80/tcp
sudo ufw allow 443/tcp
sudo ufw default deny incoming
sudo ufw default allow outgoing

Always ensure you have:

• Allowed SSH access before enabling
• Tested rules in non-production first
• Documented your firewall configuration

If automation fails:

# Check UFW status
sudo ufw status verbose

# View logs
sudo journalctl -u ufw -f

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When automating server provisioning, especially with infrastructure-as-code tools like Ansible or plain Bash scripts, encountering interactive prompts can break your automation flow. The ufw enable command is particularly problematic because it requires manual confirmation:

sudo ufw enable
Command may disrupt existing ssh connections. Proceed with operation (y|n)?

Here are three reliable methods to bypass the interactive prompt:

Method 1: Using yes Command

The simplest approach uses the yes utility to pipe 'y' automatically:

yes | sudo ufw enable

Method 2: --force Parameter

For newer UFW versions (17.04+), use the non-interactive flag:

sudo ufw --force enable

Method 3: Expect Script

For complex automation scenarios requiring multiple interactions:

#!/usr/bin/expect
spawn sudo ufw enable
expect "Proceed with operation" {send "y\r"}
expect eof

For robust deployment scripts, combine UFW automation with error handling:

#!/bin/bash

enable_ufw() {
    if ufw status | grep -q "inactive"; then
        echo "Enabling UFW firewall..."
        if yes | sudo ufw enable 2>&1 | grep -v "Skipping"; then
            echo "UFW enabled successfully"
            return 0
        else
            echo "Failed to enable UFW" >&2
            return 1
        fi
    else
        echo "UFW already active"
        return 0
    fi
}

enable_ufw || exit 1

Sometimes the prompt might still appear due to:

• Custom UFW configurations
• Modified sudoers policies
• Non-standard UFW installations

For these cases, pre-set the default policy:

sudo ufw default deny incoming
sudo ufw default allow outgoing

The order matters - setting defaults first often prevents the confirmation prompt.

Always verify SSH access rules before enabling UFW in automation:

sudo ufw allow OpenSSH
sudo ufw limit 22/tcp  # Alternative rate-limiting approach

Test connectivity in a separate terminal before running automation scripts that might lock you out of the server.