f2b - Modern Fail2Ban CLI Wrapper

A modern, secure, and extensible Go CLI tool for managing Fail2Ban jails and bans. Built with Go, featuring automatic sudo privilege management, shell completion, and comprehensive security.

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🚀 Quick Start

Prerequisites

• Go 1.25+ (for building from source)
• Fail2Ban installed and running
• Appropriate privileges (root, sudo group, or sudo access) for ban operations

Installation

Download Pre-built Binary

Download the latest release for your platform from the releases page.

# Linux (amd64)
wget https://github.com/ivuorinen/f2b/releases/latest/download/f2b_Linux_x86_64.tar.gz
tar -xzf f2b_Linux_x86_64.tar.gz
sudo mv f2b /usr/local/bin/

# macOS (Apple Silicon)
wget https://github.com/ivuorinen/f2b/releases/latest/download/f2b_Darwin_arm64.tar.gz
tar -xzf f2b_Darwin_arm64.tar.gz
sudo mv f2b /usr/local/bin/

Using Homebrew (macOS/Linux)

brew tap ivuorinen/tap
brew install f2b

Using Go

# Install latest version
go install github.com/ivuorinen/f2b@latest

# Install specific version
go install github.com/ivuorinen/f2b@v1.2.3

Using Docker (Multi-Architecture)

# Pull latest multi-architecture image
docker pull ghcr.io/ivuorinen/f2b:latest

# Run with mounted fail2ban directory
docker run --rm -v /etc/fail2ban:/etc/fail2ban:ro ghcr.io/ivuorinen/f2b:latest status all

# Architecture-specific images available:
# ghcr.io/ivuorinen/f2b:latest-amd64
# ghcr.io/ivuorinen/f2b:latest-arm64
# ghcr.io/ivuorinen/f2b:latest-armv7

Build from Source

# Clone and build
git clone https://github.com/ivuorinen/f2b.git
cd f2b
make build

# Or with custom version
go build -ldflags "-X github.com/ivuorinen/f2b/cmd.version=1.2.3" -o f2b .

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✨ Key Features

🔐 Enterprise-Grade Security

• Smart Privilege Management: Automatic sudo detection and escalation only when needed
• Advanced Input Validation: Comprehensive path traversal attack protections
• Zero Shell Injection: Secure command execution using argument arrays exclusively
• Context-Aware Operations: Timeout handling and graceful cancellation preventing hanging
• Thread-Safe Operations: Concurrent access protection with proper synchronization

🚀 Modern CLI Experience

• Comprehensive Command Set: From basic ban/unban to advanced metrics and logs-watch
• Multi-Shell Completion: Full support for bash, zsh, fish, and PowerShell
• Intuitive Command Aliases: ls-jails, st, b, ub for faster workflows
• Dual Output Formats: Human-readable plain text and machine-parseable JSON
• Structured Logging: Configurable levels with contextual information

📊 Performance & Monitoring

• Real-Time Metrics: Built-in performance monitoring via f2b metrics command
• Validation Caching: Intelligent caching reduces repeated computations by up to 70%
• Parallel Processing: Advanced concurrent operations for multi-jail scenarios
• Resource Management: Proper cleanup and timeout handling for enterprise reliability
• Performance Optimization: Context-aware operations with configurable timeouts

🛡️ Advanced Security Testing

• Extensive Path Traversal Protections: Including Unicode normalization and mixed-case attacks
• Comprehensive Test Coverage: High coverage across packages
• Mock-Only Testing: Never executes real sudo commands during testing
• Thread Safety: Extensive race condition testing and protection
• Security Audit Trail: Comprehensive logging of all privileged operations

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📋 Usage Examples

Basic Operations

# List all jails (aliases: ls-jails, jails)
f2b list-jails

# Show status (aliases: st, stat)
f2b status all
f2b status sshd

# Ban/unban IPs (aliases: b/banip, ub/unbanip)
f2b ban 192.168.1.100
f2b ban 192.168.1.100 sshd
f2b unban 192.168.1.100

# Check if IP is banned
f2b test 192.168.1.100

Advanced Features

# JSON output for scripting and automation
f2b banned all --format=json | jq '.[] | select(.Remaining | test("^0[01]:"))'

# Real-time performance metrics and monitoring
f2b metrics                    # Human-readable metrics
f2b metrics --format=json      # Machine-parseable metrics

# Advanced log monitoring with filtering and real-time watching
f2b logs sshd --limit 50                    # Recent jail logs
f2b logs-watch all 192.168.1.100           # Real-time IP monitoring
f2b logs-watch sshd --limit 100             # Live jail monitoring

# Service management with context-aware timeout handling
f2b service status             # Fail2Ban service status
f2b service restart            # Restart with automatic sudo
f2b service stop               # Stop service gracefully

# Filter testing with comprehensive validation
f2b test-filter sshd          # Test jail filter configuration
f2b test-filter apache        # Validate Apache filter

# Parallel processing for enterprise-scale operations
f2b banned all                # Automatic parallel jail processing
f2b status all                # Concurrent status for all jails
f2b list-jails                # Fast jail enumeration

# Advanced IP testing and validation
f2b test 192.168.1.100        # Check ban status across all jails
f2b test 2001:db8::1          # IPv6 support

Shell Completion

# Bash
source <(f2b completion bash)
# Or install system-wide:
f2b completion bash > /etc/bash_completion.d/f2b

# Zsh
f2b completion zsh > "${fpath[1]}/_f2b"

# Fish
f2b completion fish > ~/.config/fish/completions/f2b.fish

# PowerShell
f2b completion powershell | Out-String | Invoke-Expression

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⚙️ Configuration

Environment Variables

# Core Configuration
F2B_LOG_DIR=/var/log                    # Fail2Ban log directory
F2B_FILTER_DIR=/etc/fail2ban/filter.d   # Filter directory
F2B_LOG_LEVEL=info                      # Log level (debug,info,warn,error)
F2B_LOG_FILE=/path/to/f2b.log          # f2b's own log file

# Performance & Timeout Configuration
F2B_COMMAND_TIMEOUT=30s                 # Individual command timeout
F2B_FILE_TIMEOUT=10s                    # File operation timeout
F2B_PARALLEL_TIMEOUT=60s                # Parallel operation timeout

# Testing & Development
F2B_TEST_SUDO=false                     # Enable sudo checking in tests
F2B_VERBOSE_TESTS=false                 # Force verbose logging in CI/tests
ALLOW_DEV_PATHS=false                   # Allow /tmp paths (development only)

Global Flags

# Core Configuration
--log-dir string         # Override log directory
--filter-dir string      # Override filter directory
--format string          # Output format (plain|json)
--log-level string       # Logging level (debug,info,warn,error)
--log-file string        # Log file path for f2b operations

# Performance & Timeout Control
--command-timeout duration   # Timeout for individual fail2ban commands
--file-timeout duration      # Timeout for file operations
--parallel-timeout duration  # Timeout for parallel operations

# Output Control
--limit int              # Limit output lines (for log commands)

Command-Line Examples

# Custom directories for non-standard installations
F2B_LOG_DIR=/custom/log F2B_FILTER_DIR=/custom/filters f2b status all

# JSON output for scripting and automation
f2b banned all --format=json | jq '.[] | select(.Remaining | test("^0[01]:"))'

# Efficient log monitoring with limits
f2b logs sshd --limit 50 --format=json

# Debug mode with file logging
f2b --log-level=debug --log-file=/tmp/f2b-debug.log ban 192.168.1.100

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🔐 Security & Privileges

f2b is designed with security as a fundamental principle:

• Smart Privilege Management: Automatic sudo detection and escalation only when needed
• Input Validation: Comprehensive validation of all user input (IPs, jail names, etc.)
• Safe Execution: No shell injection vulnerabilities; uses argument arrays exclusively
• Clear Error Guidance: Helpful messages when privileges are insufficient

Command Privilege Requirements

Require sudo: ban, unban, service operations No sudo needed: status, list-jails, test, logs, version, completion

For detailed security practices, threat model, and contribution security guidelines, see docs/security.md.

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📖 Complete Command Reference

Core Commands

# Core Jail & IP Management
f2b list-jails                         # List all available jails (aliases: ls-jails, jails)
f2b status all                         # Show status of all jails (alias: st, stat)
f2b status <jail>                      # Show specific jail status with detailed info
f2b banned all                         # Show all banned IPs across all jails
f2b banned <jail>                      # Show banned IPs for specific jail with timestamps

# IP Ban/Unban Operations (Context-Aware with Timeout)
f2b ban <ip> [jail]                    # Ban IP globally or in specific jail (aliases: b, banip)
f2b unban <ip> [jail]                  # Unban IP globally or from specific jail (aliases: ub, unbanip)
f2b test <ip>                          # Check ban status across all jails with details

# Advanced Log Management & Real-Time Monitoring
f2b logs <jail> [ip] --limit N         # Show recent jail logs with optional IP filtering
f2b logs-watch <jail> [ip] --limit N   # Real-time log monitoring with live updates
f2b logs sshd --limit 100              # Show last 100 lines from sshd jail
f2b logs-watch all 192.168.1.100       # Monitor all jails for specific IP

# Service Control with Automatic Privilege Management
f2b service status                     # Show detailed Fail2Ban service status
f2b service start                      # Start Fail2Ban service with auto-sudo
f2b service stop                       # Stop Fail2Ban service gracefully
f2b service restart                    # Restart service with context-aware timeout

# Filter Testing & Validation
f2b test-filter <jail>                 # Test and validate jail filter configuration
f2b test-filter sshd                   # Validate sshd filter with comprehensive checks

# Performance Monitoring & Metrics
f2b metrics                            # Show comprehensive performance metrics
f2b metrics --format=json              # Detailed metrics in machine-readable format

# Utility & Completion Commands
f2b version                            # Show version, build info, and system details
f2b completion <shell>                 # Generate completion for bash/zsh/fish/powershell
f2b help [command]                     # Context-sensitive help with examples

Command Aliases

For convenience, most commands have short aliases:

• list-jails → ls-jails, jails
• status → st, stat, show-status
• ban → banip, b
• unban → unbanip, ub

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🏗️ Architecture

f2b is built as an enterprise-grade Go application following modern architectural principles:

🎯 Core Design Principles

• Security-First Architecture: Automatic privilege management with extensive path traversal protections
• Context-Aware Operations: Comprehensive timeout handling and graceful cancellation throughout
• Performance-Optimized: Validation caching, parallel processing, and optimized parsing algorithms
• Interface-Based Design: Full dependency injection for testing and extensibility
• Thread-Safe Operations: Proper synchronization and concurrent access protection

📊 Quality Metrics

• Test Coverage: 76.8% (cmd/), 59.3% (fail2ban/) - Above industry standards
• Modern Testing: Fluent testing framework reducing code duplication by 60-70%
• Security Testing: 13 comprehensive attack vector test cases implemented
• Performance: Context-aware operations with configurable timeouts and resource management

🛠️ Technology Stack

• Language: Go 1.25+ with modern idioms and patterns
• CLI Framework: Cobra with comprehensive command structure and shell completion
• Logging: Structured logging with Logrus and contextual information
• Testing: Advanced mock patterns with thread-safe implementations
• Deployment: Multi-architecture Docker support (amd64, arm64, armv7) with manifests
• Performance: Object pooling, validation caching, and parallel processing

🎪 Advanced Features

• 13 Commands: Comprehensive functionality from basic operations to advanced monitoring
• Parallel Processing: Automatic concurrent operations for multi-jail scenarios
• Real-Time Monitoring: Live metrics collection and performance analysis
• Enterprise Security: Advanced input validation and privilege management
• Cross-Platform: Full support for Linux, macOS, Windows, and BSD systems

For detailed architecture information, implementation patterns, and extension guidelines, see docs/architecture.md.

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🧪 Development & Testing

Quick Start

# Run all tests
go test ./...

# Run with coverage
go test -coverprofile=coverage.out ./...

# Security-focused testing with enhanced validation
F2B_TEST_SUDO=true go test ./fail2ban -run TestSudo

# Test modern fluent framework
go test ./cmd -run TestCommand

# Run parallel processing tests
go test ./fail2ban -run TestParallel

For comprehensive testing guidelines, mock patterns, and security testing practices, see docs/testing.md.

Code Quality & Linting

This project uses pre-commit for unified linting and formatting. Install the development dependencies and hooks:

make dev-deps
make pre-commit-setup

Run all linters:

# Preferred method (unified tooling)
make lint

# Run specific hooks
pre-commit run yamlfmt --all-files
pre-commit run golangci-lint --all-files

For detailed information about linting tools and configuration, see docs/linting.md.

Integration Examples

# Bash script integration
#!/bin/bash
BANNED_IPS=$(f2b banned all --format=json | jq -r '.[].IP')
for ip in $BANNED_IPS; do
    echo "Processing banned IP: $ip"
done

# Monitoring script
f2b logs-watch all --limit 20 | while read line; do
    echo "$(date): $line" >> /var/log/f2b-monitor.log
done

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🚀 Releases

Creating a New Release

Releases are automated using GoReleaser. To create a new release:

1. Tag the release:

git tag -a v1.2.3 -m "Release v1.2.3"
git push origin v1.2.3

2. GitHub Actions will automatically:

• Build binaries for multiple platforms (Linux, macOS, Windows, BSD)
• Create a GitHub release with changelog
• Upload release artifacts
• Build and push Docker images
• Update Homebrew tap (if configured)
• Generate .deb, .rpm, and .apk packages

Manual Release (Development)

# Check GoReleaser configuration
make release-check

# Create a snapshot release (no tag required)
make release-snapshot

# Create a full release (requires git tag)
make release

Release Artifacts

Each release includes:

• Pre-built binaries for multiple platforms and architectures (Linux, macOS, Windows, BSD)
• Multi-architecture Docker images (amd64, arm64, armv7) with manifests
• SHA256 checksums file
• Source code archives
• Docker images at ghcr.io/ivuorinen/f2b with architecture-specific tags
• Linux packages (.deb, .rpm, .apk) for multiple architectures

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🤝 Contributing

We welcome contributions! To get started:

• Open an issue for bugs, feature requests, or questions
• Fork the repository and create a feature branch for your changes
• Write clear commit messages and keep pull requests focused and well-documented
• Add or update tests for any code changes
• Run go test ./... and ensure all tests pass before submitting a PR
• Be respectful and constructive in all communications

For larger changes or proposals, please open an issue to discuss your ideas first.

Please see:

• CONTRIBUTING.md - Contribution guidelines
• AGENTS.md - Guidelines for AI/LLM contributors
• CODE_OF_CONDUCT.md - Community standards
• docs/architecture.md - System architecture and design
• docs/security.md - Security practices and guidelines
• docs/testing.md - Testing strategies and patterns

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📄 License

MIT License.

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👨‍💻 Author

Ismo Vuorinen (@ivuorinen)

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🆘 Support

• 📝 Open an issue
• 📖 Read the FAQ

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Built with ❤️ and Go. Securing systems one ban at a time.