systemd-timesyncd Linux: Complete Guide to Network Time Synchronization

Time synchronization is a critical aspect of system administration that ensures your Linux servers maintain accurate time across distributed networks. The systemd-timesyncd service provides a lightweight, built-in solution for network time synchronization that has become the default time sync mechanism in modern systemd-based Linux distributions.

In this comprehensive guide, we’ll explore everything you need to know about systemd-timesyncd, from basic configuration to advanced troubleshooting techniques.

What is systemd-timesyncd?

systemd-timesyncd is a system service that implements SNTP (Simple Network Time Protocol) client functionality. It’s designed as a minimal NTP client that focuses on querying time from remote NTP servers and gradually adjusting the local system clock to maintain accuracy.

Unlike full-featured NTP implementations like ntpd or chrony, systemd-timesyncd is specifically designed for client-only scenarios and doesn’t provide server functionality. This makes it perfect for desktop systems, laptops, and servers that need to synchronize time but don’t need to serve time to other systems.

Key Features of systemd-timesyncd

• Lightweight implementation – Minimal resource usage
• Automatic fallback – Uses multiple time servers for reliability
• Gradual adjustment – Smoothly adjusts time to prevent system disruption
• IPv4 and IPv6 support – Works with both protocol versions
• Network awareness – Adapts to network connectivity changes

Checking systemd-timesyncd Status

Before diving into configuration, let’s examine how to check the current status of time synchronization on your system.

Basic Status Check

sudo systemctl status systemd-timesyncd

Example Output:

● systemd-timesyncd.service - Network Time Synchronization
     Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
     Active: active (running) since Tue 2025-08-26 02:30:15 IST; 18min ago
       Docs: man:systemd-timesyncd.service(8)
   Main PID: 1247 (systemd-timesyn)
     Status: "Initial synchronization to time server 91.189.91.157:123 (ntp.ubuntu.com)."
      Tasks: 2 (limit: 4915)
     Memory: 1.4M
        CPU: 31ms
     CGroup: /system.slice/systemd-timesyncd.service
             └─1247 /lib/systemd/systemd-timesyncd

Aug 26 02:30:15 ubuntu-server systemd[1]: Starting Network Time Synchronization...
Aug 26 02:30:15 ubuntu-server systemd-timesyncd[1247]: Initial synchronization to time server 91.189.91.157:123 (ntp.ubuntu.com).
Aug 26 02:30:15 ubuntu-server systemd[1]: Started Network Time Synchronization.

Detailed Time Synchronization Status

timedatectl status

Example Output:

               Local time: Tue 2025-08-26 02:48:32 IST
           Universal time: Mon 2025-08-25 21:18:32 UTC
                 RTC time: Mon 2025-08-25 21:18:32
                Time zone: Asia/Kolkata (IST, +0530)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

The key indicators in this output are:

• System clock synchronized: yes – Indicates successful time sync
• NTP service: active – Shows that time synchronization is working

Configuration Files and Settings

systemd-timesyncd uses configuration files to determine its behavior. Understanding these files is crucial for proper time synchronization setup.

Main Configuration File

The primary configuration file is located at /etc/systemd/timesyncd.conf. Let’s examine its structure:

sudo nano /etc/systemd/timesyncd.conf

Default Configuration Example:

#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.
#
# Entries in this file show the compile time defaults.
# You can change settings by editing this file.
# Defaults can be restored by simply deleting this file.
#
# See timesyncd.conf(5) for details.

[Time]
#NTP=
#FallbackNTP=0.debian.pool.ntp.org 1.debian.pool.ntp.org 2.debian.pool.ntp.org 3.debian.pool.ntp.org
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048

Key Configuration Parameters

Configuring Custom NTP Servers

While the default configuration works well for most scenarios, you might need to configure custom NTP servers for specific requirements such as using internal time servers or regional servers for better accuracy.

Setting Primary NTP Servers

sudo nano /etc/systemd/timesyncd.conf

Custom Configuration Example:

[Time]
NTP=0.pool.ntp.org 1.pool.ntp.org time.google.com
FallbackNTP=2.pool.ntp.org 3.pool.ntp.org
RootDistanceMaxSec=5
PollIntervalMinSec=32
PollIntervalMaxSec=2048

After making changes, restart the service:

sudo systemctl restart systemd-timesyncd

Using Regional NTP Servers

For better accuracy and reduced network latency, consider using regional NTP servers:

[Time]
# For Asia region
NTP=0.asia.pool.ntp.org 1.asia.pool.ntp.org 2.asia.pool.ntp.org
# For Europe region
#NTP=0.europe.pool.ntp.org 1.europe.pool.ntp.org 2.europe.pool.ntp.org
# For North America region
#NTP=0.north-america.pool.ntp.org 1.north-america.pool.ntp.org 2.north-america.pool.ntp.org

Managing systemd-timesyncd Service

Proper service management ensures reliable time synchronization. Here are the essential commands for managing systemd-timesyncd.

Service Control Commands

# Start the service
sudo systemctl start systemd-timesyncd

# Stop the service
sudo systemctl stop systemd-timesyncd

# Restart the service
sudo systemctl restart systemd-timesyncd

# Enable service at boot
sudo systemctl enable systemd-timesyncd

# Disable service at boot
sudo systemctl disable systemd-timesyncd

# Check service status
sudo systemctl status systemd-timesyncd

Forcing Immediate Synchronization

Sometimes you need to force an immediate time synchronization, especially after system boot or network connectivity restoration:

sudo systemctl restart systemd-timesyncd

You can monitor the synchronization process in real-time:

sudo journalctl -u systemd-timesyncd -f

Example Output:

Aug 26 02:48:15 ubuntu-server systemd-timesyncd[1247]: Timed out waiting for reply from 91.189.91.157:123 (ntp.ubuntu.com).
Aug 26 02:48:20 ubuntu-server systemd-timesyncd[1247]: Initial synchronization to time server 162.159.200.123:123 (1.pool.ntp.org).
Aug 26 02:48:20 ubuntu-server systemd-timesyncd[1247]: clock is now synced.

Monitoring and Troubleshooting

Effective monitoring and troubleshooting are essential for maintaining reliable time synchronization. Let’s explore various techniques and tools.

Checking Synchronization Details

timedatectl show-timesync

Example Output:

LinkNTPServers=
SystemNTPServers=
FallbackNTPServers=0.debian.pool.ntp.org 1.debian.pool.ntp.org 2.debian.pool.ntp.org 3.debian.pool.ntp.org
ServerName=1.pool.ntp.org
ServerAddress=162.159.200.123
RootDistanceMaxUSec=5s
PollIntervalMinUSec=32s
PollIntervalMaxUSec=34min 8s
PollIntervalUSec=2min 8s
NTPMessage={ Leap=0, Version=4, Mode=4, Stratum=3, Precision=-25, RootDelay=29.449ms, RootDispersion=45.776ms, Reference=C342F10A, OriginateTimestamp=Mon 2025-08-25 21:18:32 UTC, ReceiveTimestamp=Mon 2025-08-25 21:18:32 UTC, TransmitTimestamp=Mon 2025-08-25 21:18:32 UTC, DestinationTimestamp=Mon 2025-08-25 21:18:32 UTC, Ignored=no, PacketCount=1, Jitter=0 }
Frequency=0

Monitoring Service Logs

Logs provide valuable insights into time synchronization behavior:

# View recent logs
sudo journalctl -u systemd-timesyncd --since "1 hour ago"

# View logs with timestamps
sudo journalctl -u systemd-timesyncd -o short-precise

# Follow logs in real-time
sudo journalctl -u systemd-timesyncd -f

Common Issues and Solutions

Issue 1: Time Synchronization Not Working

Symptoms:

• System clock synchronized: no in timedatectl output
• Service shows “waiting for reply” messages

Solution:

# Check network connectivity
ping 0.pool.ntp.org

# Verify DNS resolution
nslookup 0.pool.ntp.org

# Check firewall rules
sudo ufw status
sudo iptables -L | grep 123

# Test with different NTP servers
sudo nano /etc/systemd/timesyncd.conf
# Add: NTP=time.google.com time.cloudflare.com
sudo systemctl restart systemd-timesyncd

Issue 2: Large Time Jumps

Symptoms:

• System time suddenly changes by significant amounts
• Applications experiencing timestamp issues

Solution:

# Check RTC (Hardware Clock)
sudo hwclock --show

# Sync RTC with system clock
sudo hwclock --systohc

# Set smaller polling intervals for more frequent sync
[Time]
PollIntervalMinSec=32
PollIntervalMaxSec=1024

Advanced Configuration Scenarios

Let’s explore advanced configuration scenarios that you might encounter in enterprise environments or specialized setups.

Corporate Network Configuration

In corporate environments, you might need to use internal NTP servers:

[Time]
NTP=ntp1.company.com ntp2.company.com
FallbackNTP=0.pool.ntp.org 1.pool.ntp.org
RootDistanceMaxSec=10
PollIntervalMinSec=64
PollIntervalMaxSec=1024

High-Precision Time Requirements

For applications requiring high-precision time synchronization:

[Time]
NTP=time.google.com time.facebook.com time.cloudflare.com
FallbackNTP=0.pool.ntp.org 1.pool.ntp.org
RootDistanceMaxSec=1
PollIntervalMinSec=16
PollIntervalMaxSec=512

Offline or Isolated Networks

For systems that occasionally connect to the internet:

[Time]
NTP=
FallbackNTP=0.pool.ntp.org 1.pool.ntp.org 2.pool.ntp.org 3.pool.ntp.org
RootDistanceMaxSec=10
PollIntervalMinSec=32
PollIntervalMaxSec=2048

Integration with System Services

Understanding how systemd-timesyncd integrates with other system services helps in troubleshooting and optimization.

Dependency Management

Check which services depend on time synchronization:

systemctl list-dependencies systemd-timesyncd
systemctl list-dependencies --reverse systemd-timesyncd

Network Dependency

systemd-timesyncd automatically starts after network connectivity is established:

systemctl show systemd-timesyncd | grep -E "(After|Wants|Requires)"

Example Output:

After=systemd-remount-fs.service systemd-tmpfiles-setup.service system.slice sysinit.target systemd-sysusers.service
Wants=network-online.target
Requires=system.slice sysinit.target

Performance Optimization

Optimizing systemd-timesyncd performance ensures efficient resource usage while maintaining accuracy.

Polling Strategy Optimization

[Time]
# Conservative approach for servers
PollIntervalMinSec=64
PollIntervalMaxSec=2048

# Aggressive approach for desktop systems
PollIntervalMinSec=32
PollIntervalMaxSec=1024

# Balanced approach
PollIntervalMinSec=32
PollIntervalMaxSec=2048

Server Selection Strategy

Choose NTP servers based on:

• Geographic proximity – Reduces network latency
• Network path – Fewer hops mean better accuracy
• Server reliability – Use well-maintained time servers
• Load distribution – Avoid overloading single servers

Security Considerations

Time synchronization security is crucial for maintaining system integrity and preventing time-based attacks.

Network Security

# Allow NTP traffic through firewall
sudo ufw allow out 123/udp
sudo ufw allow in 123/udp

# Block unnecessary NTP traffic
sudo iptables -A OUTPUT -p udp --dport 123 -j ACCEPT
sudo iptables -A OUTPUT -p udp -j DROP

Authentication Considerations

While systemd-timesyncd doesn’t support NTP authentication, you can:

• Use trusted NTP server sources
• Implement network-level security
• Monitor time synchronization logs for anomalies
• Consider upgrading to chrony for authentication support if needed

Migration from Other NTP Implementations

If you’re migrating from other NTP implementations, here’s how to ensure a smooth transition.

From ntpd to systemd-timesyncd

# Stop and disable ntpd
sudo systemctl stop ntp
sudo systemctl disable ntp

# Enable systemd-timesyncd
sudo systemctl enable systemd-timesyncd
sudo systemctl start systemd-timesyncd

# Verify transition
timedatectl status

From chrony to systemd-timesyncd

# Stop and disable chrony
sudo systemctl stop chronyd
sudo systemctl disable chronyd

# Enable systemd-timesyncd
sudo systemctl enable systemd-timesyncd
sudo systemctl start systemd-timesyncd

# Check synchronization
timedatectl show-timesync

Best Practices and Recommendations

Follow these best practices to ensure reliable time synchronization:

Configuration Best Practices

• Use multiple time sources – Configure at least 3-4 NTP servers
• Choose reliable servers – Use well-maintained pool servers
• Consider geographic location – Use regional servers for better accuracy
• Set appropriate polling intervals – Balance accuracy with network usage
• Monitor synchronization status – Regularly check time sync health

Monitoring and Maintenance

# Create a monitoring script
#!/bin/bash
# Time sync health check

SYNC_STATUS=$(timedatectl status | grep "System clock synchronized" | awk '{print $4}')
NTP_SERVICE=$(timedatectl status | grep "NTP service" | awk '{print $3}')

if [[ "$SYNC_STATUS" == "yes" && "$NTP_SERVICE" == "active" ]]; then
    echo "Time synchronization is healthy"
    exit 0
else
    echo "Time synchronization issue detected"
    echo "Sync Status: $SYNC_STATUS"
    echo "NTP Service: $NTP_SERVICE"
    exit 1
fi

Conclusion

systemd-timesyncd provides a robust, lightweight solution for network time synchronization in modern Linux environments. Its simplicity and integration with systemd make it an excellent choice for most desktop and server scenarios where client-only time synchronization is sufficient.

Key takeaways from this guide:

• systemd-timesyncd is enabled by default on most systemd-based distributions
• Configuration is straightforward through /etc/systemd/timesyncd.conf
• Monitoring and troubleshooting use familiar systemd tools
• The service handles network connectivity changes gracefully
• For advanced features like authentication, consider alternatives like chrony

Regular monitoring and proper configuration ensure that your systems maintain accurate time, which is essential for logging, security, distributed systems, and compliance requirements. Whether you’re managing a single desktop or a fleet of servers, understanding systemd-timesyncd empowers you to maintain reliable time synchronization across your Linux infrastructure.