Time Synchronization FAQ

This guide answers common questions about time synchronization, NTP servers, and best practices for keeping your systems accurately synchronized.

General Questions

What is NTP?

NTP (Network Time Protocol) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. It provides accurate time synchronization with millisecond precision.

Why is accurate time important?

Accurate time synchronization is crucial for:

Security: Certificate validation, authentication logs, and security protocols
Distributed Systems: Database consistency, transaction ordering, and coordination
Compliance: Regulatory requirements for audit trails and timestamps
Debugging: Correlating logs across multiple systems
Financial Transactions: Precise timing for trading and payment processing

What’s the difference between NTP and Roughtime?

NTP: Traditional protocol providing high precision time synchronization
Roughtime: Modern, secure protocol with cryptographic guarantees against network attacks
Best Practice: Use both - Roughtime for security, NTP for precision

Using Xerobi NTP Servers

How do I configure my system to use time.xerobi.com?

Linux (systemd):

# Edit /etc/systemd/timesyncd.conf
sudo nano /etc/systemd/timesyncd.conf

# Add or modify:
NTP=time.xerobi.com
FallbackNTP=ntp.ubuntu.com

# Restart the service
sudo systemctl restart systemd-timesyncd

Linux (chrony):

# Edit /etc/chrony/chrony.conf
sudo nano /etc/chrony/chrony.conf

# Add:
server time.xerobi.com iburst

# Restart chrony
sudo systemctl restart chrony

Windows:

# Open PowerShell as Administrator
w32tm /config /manualpeerlist:time.xerobi.com /syncfromflags:manual /reliable:yes /update
w32tm /resync

What ports need to be open?

NTP: UDP port 123
Roughtime: TCP port 2002

Is there any rate limiting?

Our NTP servers are provided free of charge with reasonable usage limits. For high-volume applications, consider using multiple NTP servers or implementing local NTP servers.

Troubleshooting

My system isn’t synchronizing

Check firewall settings:

# Linux
sudo ufw allow 123/udp
# or
sudo iptables -A INPUT -p udp --dport 123 -j ACCEPT

Verify NTP service status:

# systemd
systemctl status systemd-timesyncd

# chrony
chronyc sources
chronyc tracking

Check time difference:

# Quick check
ntpdate -q time.xerobi.com

I’m getting “no server suitable for synchronization”

This usually means:

Firewall blocking NTP traffic
Incorrect server configuration
Network connectivity issues
NTP service not running

How do I verify synchronization is working?

Linux:

timedatectl status
ntpstat

Windows:

w32tm /query /status

Check offset:

# Using ntpdate
ntpdate -q time.xerobi.com

# Using chronyc
chronyc tracking

Best Practices

Redundancy

Always configure multiple NTP servers:

# /etc/systemd/timesyncd.conf
NTP=time.xerobi.com ntp.ubuntu.com time.nist.gov

Monitoring

Monitor your time synchronization:

# Check offset regularly
chronyc tracking | grep "System time"

# Alert if offset > 100ms
#!/bin/bash
OFFSET=$(chronyc tracking | grep "System time" | awk '{print $4}')
if (( $(echo "$OFFSET > 0.1" | bc -l) )); then
    echo "Time offset too high: $OFFSET seconds"
fi

Security Considerations

Use authenticated NTP when possible (NTPv4 with autokey)
Implement Roughtime for cryptographic security
Monitor for time jumps that could indicate attacks
Use local NTP servers for internal networks

Advanced Configuration

NTP Pool Configuration

For high availability, use NTP pools:

# /etc/ntp.conf
server 0.pool.ntp.org
server 1.pool.ntp.org
server time.xerobi.com

Custom NTP Server Setup

If you need your own NTP server:

# Install NTP
sudo apt install ntp

# Configure upstream servers
# /etc/ntp.conf
server time.xerobi.com prefer
server ntp.ubuntu.com

# Configure as server
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery
restrict 127.0.0.1
restrict -6 ::1

Common Issues and Solutions

Large time jumps

Cause: System clock was significantly off Solution: Use ntpd instead of ntpdate for gradual correction

NTP socket in use

Cause: Multiple NTP services running Solution:

sudo systemctl stop ntp
sudo systemctl disable ntp
sudo systemctl enable systemd-timesyncd

DNS resolution failures

Cause: DNS issues preventing server lookup Solution: Use IP addresses directly or fix DNS configuration

Performance Tuning

For low-latency applications

# /etc/chrony/chrony.conf
server time.xerobi.com iburst minpoll 4 maxpoll 6
makestep 0.1 3

For power-constrained devices

# Less frequent polling
server time.xerobi.com minpoll 8 maxpoll 12

Monitoring and Alerting

NTP Monitoring Script

#!/bin/bash
# ntp-monitor.sh

SERVERS=("time.xerobi.com" "ntp.ubuntu.com")
THRESHOLD=0.5  # seconds

for server in "${SERVERS[@]}"; do
    if ntpdate -q "$server" >/dev/null 2>&1; then
        offset=$(ntpdate -q "$server" 2>/dev/null | tail -1 | awk '{print $9}')
        if (( $(echo "${offset#-} > $THRESHOLD" | bc -l) )); then
            echo "WARNING: High offset $offset seconds from $server"
        else
            echo "OK: $server offset $offset seconds"
        fi
    else
        echo "ERROR: Cannot reach $server"
    fi
done

Support

If you’re still having issues:

Check our NTP Servers documentation
Visit the NTP Pool status page
Contact support at [email protected] with:
- Your operating system and version
- NTP client configuration
- Error messages
- Network setup details

NTP Documentation

Complete NTP server documentation

NTP Pool Project

Join the NTP Pool project

Chrony Documentation

Advanced NTP client documentation

Roughtime Specification

Roughtime protocol details

Getting Started

Integration Guides

API FAQs

Time Synchronization FAQ

Time Synchronization FAQ

General Questions

What is NTP?

Why is accurate time important?

What’s the difference between NTP and Roughtime?

Using Xerobi NTP Servers

How do I configure my system to use time.xerobi.com?

What ports need to be open?

Is there any rate limiting?

Troubleshooting

My system isn’t synchronizing

I’m getting “no server suitable for synchronization”

How do I verify synchronization is working?

Best Practices

Redundancy

Monitoring

Security Considerations

Advanced Configuration

NTP Pool Configuration

Custom NTP Server Setup

Common Issues and Solutions

Large time jumps

NTP socket in use

DNS resolution failures

Performance Tuning

For low-latency applications

For power-constrained devices

Monitoring and Alerting

NTP Monitoring Script

Support

NTP Documentation

NTP Pool Project

Chrony Documentation

Roughtime Specification

​Time Synchronization FAQ

​General Questions

​What is NTP?

​Why is accurate time important?

​What’s the difference between NTP and Roughtime?

​Using Xerobi NTP Servers

​How do I configure my system to use time.xerobi.com?

​What ports need to be open?

​Is there any rate limiting?

​Troubleshooting

​My system isn’t synchronizing

​I’m getting “no server suitable for synchronization”

​How do I verify synchronization is working?

​Best Practices

​Redundancy

​Monitoring

​Security Considerations

​Advanced Configuration

​NTP Pool Configuration

​Custom NTP Server Setup

​Common Issues and Solutions

​Large time jumps

​NTP socket in use

​DNS resolution failures

​Performance Tuning

​For low-latency applications

​For power-constrained devices

​Monitoring and Alerting

​NTP Monitoring Script

​Support

​Related Resources

NTP Documentation

NTP Pool Project

Chrony Documentation

Roughtime Specification

Time Synchronization FAQ

General Questions

What is NTP?

Why is accurate time important?

What’s the difference between NTP and Roughtime?

Using Xerobi NTP Servers

How do I configure my system to use time.xerobi.com?

What ports need to be open?

Is there any rate limiting?

Troubleshooting

My system isn’t synchronizing

I’m getting “no server suitable for synchronization”

How do I verify synchronization is working?

Best Practices

Redundancy

Monitoring

Security Considerations

Advanced Configuration

NTP Pool Configuration

Custom NTP Server Setup

Common Issues and Solutions

Large time jumps

NTP socket in use

DNS resolution failures

Performance Tuning

For low-latency applications

For power-constrained devices

Monitoring and Alerting

NTP Monitoring Script

Support

Related Resources