Fast commands to check DNS configuration when troubleshooting connectivity issues. See resolver settings, test resolution, diagnose common problems.

Last updated: 2025-12-20

Quick DNS Configuration Check for Linux Server Troubleshooting

Server can't resolve domain names? Applications failing with "could not resolve host"? Here's how to quickly check your DNS configuration and diagnose common problems.

For continuous DNS monitoring, see Monitor DNS Information.

30-Second DNS Health Check

# 1. What DNS servers are configured?
cat /etc/resolv.conf

# 2. Can we resolve a domain?
dig google.com +short

# 3. Is DNS actually working?
nslookup google.com

# If any of these fail, you have a DNS problem

Understanding /etc/resolv.conf

# Example output:
nameserver 8.8.8.8         # Primary DNS server
nameserver 8.8.4.4         # Secondary DNS server
search example.com         # Default search domain
options timeout:2 attempts:3

Common issues:

No nameserver lines = no DNS configured
Unreachable nameservers = network or firewall issue
Wrong search domain = internal names don't resolve

Commands to Check DNS Configuration

Use these Linux commands to check DNS configuration:

Check DNS Configuration

# Check DNS configuration
cat /etc/resolv.conf

# DNS configuration with details
cat /etc/resolv.conf | grep -v "^#"

# DNS servers only
cat /etc/resolv.conf | grep nameserver

DNS Cache Statistics (systemd)

# DNS cache statistics (systemd)
sudo systemd-resolve --statistics

# DNS cache with details
sudo systemd-resolve --status

# DNS cache flush
sudo systemd-resolve --flush-caches

Test DNS Resolution

# Test DNS resolution
nslookup example.com

# DNS resolution with dig
dig example.com

# DNS resolution with host
host example.com

# Reverse DNS lookup
nslookup <IP_ADDRESS>

Check DNS Servers

# Check DNS servers
cat /etc/resolv.conf | grep nameserver

# DNS servers with IPs
cat /etc/resolv.conf | grep nameserver | awk '{print $2}'

# Test DNS server connectivity
for dns in $(cat /etc/resolv.conf | grep nameserver | awk '{print $2}'); do echo "Testing $dns"; dig @$dns example.com +short; done

Alternative Commands

# DNS configuration with search domains
cat /etc/resolv.conf | grep -E "nameserver|search"

# DNS configuration from NetworkManager
nmcli dev show | grep DNS

# DNS resolution test with timeout
timeout 5 nslookup example.com

# DNS resolution performance
time dig example.com

How to Set Up in Zuzia.app

Set up automated monitoring of DNS configuration in Zuzia.app:

Step 1: Add Scheduled Task

Add Scheduled Task
- Navigate to Zuzia.app dashboard
- Click "Add Scheduled Task"
- Choose "Command" task type
Configure Command
- Use command: cat /etc/resolv.conf
- Set execution frequency (e.g., every hour)
- Configure task name and description

Step 2: Configure Alerts

Set Alert Conditions
- Configure alerts when DNS servers change
- Set up alerts for DNS configuration changes
- Configure alerts for DNS resolution failures
Choose Notification Channels
- Configure email notifications
- Set up webhook integrations
- Configure SMS notifications (if available)

Step 3: Monitor Results

Review DNS Configuration Data
- Check dashboard for DNS server settings
- Review DNS configuration
- Identify configuration changes
Track DNS Trends
- Monitor DNS configuration over time
- Identify DNS server changes
- Detect DNS issues

Use Cases for DNS Configuration Monitoring

This monitoring helps you:

Monitor DNS Server Settings

Settings monitoring: Monitor DNS server settings continuously
Settings tracking: Track DNS server changes
Settings verification: Verify DNS server settings
Settings management: Manage DNS server settings effectively

Detect Configuration Changes

Change detection: Detect DNS configuration changes automatically
Change alerts: Alert on DNS configuration changes
Change tracking: Track configuration changes over time
Change analysis: Analyze configuration change patterns

Troubleshoot DNS Issues

Issue troubleshooting: Troubleshoot DNS issues using configuration data
Root cause analysis: Identify root causes through DNS monitoring
Problem resolution: Resolve problems based on DNS configuration
Issue tracking: Track DNS issues through monitoring

Maintain Network Connectivity

Connectivity maintenance: Maintain network connectivity through DNS monitoring
Connectivity verification: Verify network connectivity regularly
Connectivity optimization: Optimize network connectivity
Connectivity troubleshooting: Troubleshoot connectivity issues

Audit DNS Configuration

Configuration auditing: Audit DNS configuration regularly
Configuration tracking: Track configuration changes over time
Configuration documentation: Document DNS configuration
Configuration compliance: Ensure compliance with network policies

Verify DNS Setup

Setup verification: Verify DNS setup through monitoring
Setup validation: Validate DNS configuration
Setup optimization: Optimize DNS setup
Setup documentation: Document DNS setup

Advanced Options

Enhance DNS configuration monitoring with advanced options:

Compare DNS Configs Over Time

Historical comparison: Compare DNS configurations over time
Change detection: Detect DNS configuration changes automatically
Trend analysis: Analyze DNS configuration trends
Pattern detection: Detect patterns in DNS changes

Monitor DNS Resolution Performance

Performance monitoring: Monitor DNS resolution performance
Performance analysis: Analyze resolution times
Performance optimization: Optimize DNS resolution
Performance tracking: Track resolution performance over time

Track DNS Server Availability

Availability tracking: Track DNS server availability
Availability monitoring: Monitor DNS server health
Availability alerts: Alert on DNS server failures
Availability optimization: Optimize DNS server selection

Integrate with DNS Management

Management integration: Integrate with DNS management tools
Automated management: Automate DNS management
DNS optimization: Optimize DNS configuration
DNS security: Enhance DNS security

Troubleshooting DNS Issues

When monitoring shows DNS configuration changes:

Identify DNS Problems

Review DNS Configuration
- Review current DNS configuration
- Identify DNS server changes
- Check DNS resolution
Investigate DNS Issues
- Investigate why DNS configuration changed
- Check DNS server connectivity
- Verify DNS resolution

Take Action

Resolve DNS Issues
- Resolve DNS configuration issues
- Restore correct DNS servers if needed
- Update DNS configuration
Strengthen DNS Security
- Strengthen DNS security
- Implement DNS monitoring
- Review DNS policies

Best Practices for DNS Configuration Monitoring

Follow these best practices:

Monitor regularly: Monitor DNS configuration regularly
Set up alerts: Set up alerts for DNS changes
Review changes: Review DNS changes promptly
Test resolution: Test DNS resolution regularly
Document configuration: Document DNS configuration
Respond quickly: Respond to DNS issues quickly

FAQ: Common Questions About DNS Configuration Monitoring

How often should I check DNS configuration?

We recommend checking DNS configuration every hour or every few hours. DNS configuration changes are typically infrequent but important to detect quickly. More frequent checks provide better visibility but increase system load. Adjust frequency based on your network requirements and change frequency.

Can I test DNS resolution?

Yes, you can add DNS resolution tests using commands like nslookup or dig, though this requires additional monitoring setup. Test DNS resolution to verify connectivity and detect resolution issues. Regular resolution tests help maintain network connectivity.

What if DNS configuration changes?

You'll receive notifications when DNS configuration changes are detected. You can then verify whether changes are authorized or indicate a network issue. Review change details, check DNS server connectivity, verify change authorization, and take appropriate action. Quick response helps prevent connectivity issues.

Can I monitor DNS cache?

Yes, if using systemd-resolved, you can use systemd-resolve --statistics to see DNS cache statistics, though this requires root access. Monitor DNS cache to understand resolution performance and detect cache issues. Cache monitoring helps optimize DNS resolution.

How do I detect DNS resolution problems?

Detect DNS resolution problems by testing DNS resolution regularly, monitoring resolution times, checking DNS server connectivity, reviewing DNS logs, and using automated resolution tests. Resolution problems may indicate DNS server issues or network problems.

Can I track DNS changes over time?

Yes, Zuzia.app stores historical data, allowing you to track DNS changes over time. Review historical data to identify changes, compare current vs. historical DNS configs, detect unauthorized changes, and maintain audit trails. Historical data helps understand DNS evolution and detect issues.

How does AI help with DNS monitoring?

If you have Zuzia.app's full package, AI analysis can detect DNS patterns automatically, identify unusual changes, predict potential connectivity issues, suggest DNS improvements, and provide insights for improving network management. AI helps you understand DNS patterns and prevent issues proactively.

What if I have multiple DNS servers?

If you have multiple DNS servers, monitor all DNS servers, test resolution with each server, compare server performance, and configure failover appropriately. Multiple DNS servers provide redundancy and improve reliability. Monitor all servers to maintain DNS availability.

How do I prevent unauthorized DNS changes?

Prevent unauthorized DNS changes by restricting DNS configuration access, monitoring DNS changes continuously, enforcing network policies, reviewing DNS permissions regularly, and using automated monitoring. Multiple layers of security help prevent unauthorized changes.

Can I export DNS configuration data?

Yes, Zuzia.app allows you to export monitoring data. Export data for analysis, reporting, compliance, or network investigation. Use exported data to analyze DNS patterns, create network reports, and investigate DNS issues.

Related guides
- Website uptime and global reachability: How to Monitor Website Uptime, Multi-Location Website Monitoring - Detect Regional Outages
- Network connectivity and ping monitoring: Global Agent Ping Monitoring - Multi-Location Server Availability, Ping Monitoring Fundamentals - Understanding ICMP and Network Latency
Related recipes
- Check and monitor DNS information and responses: Continuous DNS Configuration Monitoring for Change Detection
- Check hostname and IP configuration: How to Check System Hostname and IP Address on Linux, How to Check System IP Address Configuration on Linux Server
- Monitor routing and network connections: How to Check Routing Table on Linux Server, How to Monitor Routing Table on Linux Server, How to Monitor Network Connections on Linux Server
Related problems
- Network connectivity incidents on Linux: Network Connectivity Issues on Linux Server
- Website unavailable because of DNS or routing issues: Website Unavailable or Down

Quick DNS Configuration Check for Linux Server Troubleshooting