How to Configure an NTP Client on AlmaLinux

In modern computing environments, maintaining precise system time is critical. From security protocols to log accuracy, every aspect of your system depends on accurate synchronization. In this guide, we will walk through the process of configuring an NTP (Network Time Protocol) client on AlmaLinux, ensuring your system is in sync with a reliable time server.

What is NTP?

NTP is a protocol used to synchronize the clocks of computers to a reference time source, like an atomic clock or a stratum-1 NTP server. Configuring your AlmaLinux system as an NTP client enables it to maintain accurate time by querying a specified NTP server.

Prerequisites

Before diving into the configuration process, ensure the following:

1. AlmaLinux is installed and up-to-date.
2. You have sudo privileges on the system.
3. Your server has network access to an NTP server, either a public server or one in your local network.

Step 1: Update Your System

Begin by updating your AlmaLinux system to ensure all installed packages are current:

sudo dnf update -y

Step 2: Install Chrony

AlmaLinux uses Chrony as its default NTP implementation. Chrony is efficient, fast, and particularly suitable for systems with intermittent connections.

To install Chrony, run:

sudo dnf install chrony -y

Verify the installation by checking the version:

chronyd -v

Step 3: Configure Chrony as an NTP Client

Chrony’s main configuration file is located at /etc/chrony.conf. Open this file with your preferred text editor:

sudo nano /etc/chrony.conf

Key Configurations

1. Specify the NTP Servers
   By default, Chrony includes public NTP pool servers. Replace or append your desired NTP servers:

   server 0.pool.ntp.org iburst
   server 1.pool.ntp.org iburst
   server 2.pool.ntp.org iburst
   server 3.pool.ntp.org iburst
   

   The iburst option ensures faster initial synchronization.

2. Set Time Zone (Optional)
   Ensure your system time zone is correct:

   timedatectl set-timezone <your-time-zone>
   

   Replace <your-time-zone> with your region, such as America/New_York.

3. Optional: Add Local Server
   If you have an NTP server in your network, replace the pool servers with your server’s IP:

   server 192.168.1.100 iburst
   

4. Other Useful Parameters

   • Minimizing jitter: Adjust poll intervals to reduce variations:

     maxpoll 10
     minpoll 6
     

   • Enabling NTP authentication (for secure environments):

     keyfile /etc/chrony.keys
     

     Configure keys for your setup.

Save and exit the editor.

Step 4: Start and Enable Chrony Service

Start the Chrony service to activate the configuration:

sudo systemctl start chronyd

Enable the service to start at boot:

sudo systemctl enable chronyd

Check the service status to ensure it’s running:

sudo systemctl status chronyd

Step 5: Test NTP Synchronization

Verify that your client is correctly synchronizing with the configured NTP servers.

1. Check Time Sources:

   chronyc sources
   

   This command will display a list of NTP servers and their synchronization status:

   MS Name/IP address         Stratum Poll Reach LastRx Last sample
   ===============================================================================
   ^* 0.pool.ntp.org               2     6    37    8   -0.543ms   +/- 1.234ms
   

   • ^* indicates the server is the current synchronization source.
   • Reach shows the number of recent responses (value up to 377 indicates stable communication).

2. Track Synchronization Progress:

   chronyc tracking
   

   This provides detailed information about synchronization, including the server’s stratum, offset, and drift.

3. Sync Time Manually: If immediate synchronization is needed:

   sudo chronyc -a makestep
   

Step 6: Configure Firewall (If Applicable)

If your server runs a firewall, ensure it allows NTP traffic through port 123 (UDP):

sudo firewall-cmd --permanent --add-service=ntp
sudo firewall-cmd --reload

Step 7: Automate Time Sync with Boot

Ensure your AlmaLinux client synchronizes time automatically after boot. Run:

sudo timedatectl set-ntp true

Troubleshooting Common Issues

1. No Time Sync:

   • Check the network connection to the NTP server.
   • Verify /etc/chrony.conf for correct server addresses.

2. Chrony Service Fails to Start:

   • Inspect logs for errors:

     journalctl -xe | grep chronyd
     

3. Client Can’t Reach NTP Server:

   • Ensure port 123/UDP is open on the server-side firewall.
   • Verify the client has access to the server via ping <server-ip>.

4. Offset Too High:

   • Force synchronization:

     sudo chronyc -a burst
     

Conclusion

Configuring an NTP client on AlmaLinux using Chrony ensures that your system maintains accurate time synchronization. Following this guide, you’ve installed Chrony, configured it to use reliable NTP servers, and verified its functionality. Whether you’re working in a small network or a larger infrastructure, precise timekeeping is now one less thing to worry about!

For additional customization or troubleshooting, refer to Chrony documentation.