cleanup_hosts.sh

macOS Hosts File Cleanup Script

A comprehensive solution for automatically removing IP address entries starting with "194.*" from the macOS /etc/hosts file on a scheduled basis.

Overview

The /etc/hosts file is a system file that maps hostnames to IP addresses, functioning as a local DNS on macOS. This script provides a safe and automated way to remove specific IP address entries while maintaining system integrity through backups, logging, and proper permission handling.

Features

• Safe removal of 194.* IP entries from /etc/hosts
• Automatic backups before making changes
• Comprehensive logging with timestamps
• DNS cache flushing for immediate effect
• Multiple scheduling options (launchd and crontab)
• Error handling and validation
• Production-ready with proper permissions and ownership

Requirements

• macOS system
• Administrative (root) privileges
• Bash shell

Installation

1. Download and Setup Script

# Make the script executable and place it in the system directory
sudo cp cleanup_hosts.sh /usr/local/bin/
sudo chmod 755 /usr/local/bin/cleanup_hosts.sh
sudo chown root:wheel /usr/local/bin/cleanup_hosts.sh

2. Verify Installation

Test the script manually:

sudo /usr/local/bin/cleanup_hosts.sh

Scheduling Options

Method 1: Using launchd (Recommended)

Launchd is the native macOS scheduling system and offers better reliability and flexibility.

Create Launch Daemon

Create the plist file at /Library/LaunchDaemons/com.local.cleanup_hosts.plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.local.cleanup_hosts</string>
    <key>ProgramArguments</key>
    <array>
        <string>/usr/local/bin/cleanup_hosts.sh</string>
    </array>
    <key>StartCalendarInterval</key>
    <dict>
        <key>Hour</key>
        <integer>0</integer>
        <key>Minute</key>
        <integer>0</integer>
    </dict>
    <key>RunAtLoad</key>
    <true/>
    <key>StandardErrorPath</key>
    <string>/var/log/cleanup_hosts_error.log</string>
    <key>StandardOutPath</key>
    <string>/var/log/cleanup_hosts_output.log</string>
</dict>
</plist>

Load the Launch Daemon

sudo launchctl load -w /Library/LaunchDaemons/com.local.cleanup_hosts.plist

Verify Installation

sudo launchctl list | grep cleanup_hosts

Method 2: Using Crontab

Alternative scheduling method using traditional Unix cron:

# Edit root crontab
sudo crontab -e

# Add this line to run daily at midnight
0 0 * * * /usr/local/bin/cleanup_hosts.sh

Script Features

Basic Functionality

• Identifies and removes lines starting with "194." from /etc/hosts
• Creates temporary files for safe processing
• Validates changes before applying
• Sets correct file permissions (644)
• Flushes DNS cache for immediate effect

Enhanced Features

• Timestamped logging to /var/log/hosts_cleaner.log
• Automatic backups with timestamp naming
• Error detection and graceful handling
• Change verification before modification
• Cleanup of temporary files

Log Files

The script generates several log files:

• /var/log/hosts_cleaner.log - Main activity log
• /var/log/cleanup_hosts_output.log - Standard output (launchd)
• /var/log/cleanup_hosts_error.log - Error output (launchd)

Backup Files

Automatic backups are created at /etc/hosts.backup.YYYYMMDDHHMMSS before each modification.

Troubleshooting

Changes Not Taking Effect

If modifications don't apply immediately:

# Manually flush DNS cache
sudo killall -HUP mDNSResponder

# Check system logs
tail -f /var/log/hosts_cleaner.log

Permission Issues

Ensure proper permissions:

sudo chmod 755 /usr/local/bin/cleanup_hosts.sh
sudo chown root:wheel /usr/local/bin/cleanup_hosts.sh

Scheduled Task Not Running

For launchd:

# Check if daemon is loaded
sudo launchctl list | grep cleanup_hosts

# Reload if necessary
sudo launchctl unload /Library/LaunchDaemons/com.local.cleanup_hosts.plist
sudo launchctl load -w /Library/LaunchDaemons/com.local.cleanup_hosts.plist

For crontab:

# Verify crontab entry
sudo crontab -l

View Recent Activity

# Check recent logs
tail -20 /var/log/hosts_cleaner.log

# Monitor real-time
tail -f /var/log/hosts_cleaner.log

Uninstallation

Remove launchd Daemon

sudo launchctl unload -w /Library/LaunchDaemons/com.local.cleanup_hosts.plist
sudo rm /Library/LaunchDaemons/com.local.cleanup_hosts.plist

Remove Crontab Entry

sudo crontab -e
# Delete the cleanup_hosts.sh line and save

Remove Files

sudo rm /usr/local/bin/cleanup_hosts.sh
sudo rm /var/log/hosts_cleaner.log
sudo rm /var/log/cleanup_hosts_*.log

Safety Features

• Backup creation before every modification
• Change validation to prevent unnecessary writes
• Temporary file processing to avoid corruption
• Permission verification and restoration
• Comprehensive logging for audit trails

Customization

To target different IP ranges, modify the grep pattern in the script:

# Current: removes 194.*
grep -v "^194\." "$HOSTS_FILE" > "$TMP_FILE"

# Example: remove 192.168.*
grep -v "^192\.168\." "$HOSTS_FILE" > "$TMP_FILE"

Contributing

Contributions are welcome! Please ensure any modifications maintain the safety features and logging capabilities.

License

[Add your license information here]

References

This implementation follows macOS best practices for system file modification and automated task scheduling.