How to Configure an NTP Server and Clients with chrony

Updated: 28 September 2026 · Applies to: chrony 4.5 to 4.8 on AlmaLinux and Rocky Linux 9 and 10, RHEL 9 and 10, Ubuntu 24.04 and 26.04, Debian 13

On a network with many servers, one of them can act as the time server for the others: it takes the time from the internet, and the rest synchronise with it. This keeps all clocks consistent even if outside access is limited. The older CentOS 7 guides used ntpd; current systems use chrony, which does both roles. The configuration below was checked with chrony 4.8 on AlmaLinux 9.

On the time server

1. Install chrony if needed: dnf install chrony or apt install chrony.
2. Edit the configuration: /etc/chrony.conf (AlmaLinux, Rocky Linux, RHEL) or a file in /etc/chrony/conf.d/ (Ubuntu, Debian). Keep the existing pool line for upstream time, and add:

   allow 192.168.10.0/24

   This lets clients in that network ask for the time. Without an allow line, chrony only acts as a client.
3. Optional: to keep serving time when the internet connection is down, add local stratum 10. The clients then stay in step with this server even without an upstream source; only use it on a single, designated time server.
4. Restart it:

   systemctl restart chronyd     # AlmaLinux, Rocky Linux, RHEL
   systemctl restart chrony      # Ubuntu, Debian

5. Open UDP port 123 for your network:

   firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="192.168.10.0/24" service name="ntp" accept'
   firewall-cmd --reload

   With UFW: ufw allow from 192.168.10.0/24 to any port 123 proto udp.

On each client

1. Point the client to your server. In /etc/chrony.conf (or a .sources file in /etc/chrony/sources.d/ on Ubuntu and Debian), replace the pool line with:

   server 192.168.10.5 iburst

2. Restart chrony and check the source:

   systemctl restart chronyd
   chronyc sources -v

   The server should be listed with ^*, which means it is in use.

Check on the server

chronyc tracking        # the server's own synchronisation
chronyc clients         # which clients have asked for the time

For a single server that only needs to keep its own clock right, see how to synchronize time with NTP on Linux.

Official documentation: chrony documentation.