--- title: "Inspecting time sync settings" slug: "compute-vpc-ntp-check" updated: 2026-09-17T09:17:55Z published: 2026-09-17T09:17:55Z canonical: "guide.ncloud-docs.com/compute-vpc-ntp-check" --- > ## Documentation Index > Fetch the complete documentation index at: https://guide.ncloud-docs.com/llms.txt > Use this file to discover all available pages before exploring further. # Inspecting time sync settings Available in VPC NAVER Cloud Platform provides an NTP server for time synchronization. Time synchronization settings have significant effects on system operation and management and are closely related to security, network communication, and data accuracy. It is recommended to use a daemon that synchronizes the time continuously rather than performs 1-time synchronization periodically. ## NAVIX, CentOS, Rocky Linux Inspect the NTP settings and file in the RedHat OS provided on NAVER Cloud Platform. Note The following guide applies to CentOS 7, Rocky Linux 8, and Rocky Linux 9. 1. Check whether chrony is installed and running. ``` [root@centos7 ~]# rpm -qa | grep chrony chrony-3.4-1.el7.x86_64 [root@centos7 ~]# ps -ef|grep chronyd | grep -v grep chrony 497 1 0 Mar27 ? 00:00:05 /usr/sbin/chronyd ``` ``` [root@rockylinux8 ~]# rpm -qa | grep chrony chrony-4.1-1.el8.rocky.0.1.x86_64 [root@rockylinux8 ~]# ps -ef | grep chronyd | grep -v grep chrony 725 1 0 Jul25 ? 00:00:05 /usr/sbin/chronyd ``` ``` [root@navix9 ~]# rpm -qa | grep chrony chrony-4.6.1-1.el9.x86_64 [rootnavix9 ~]# ps -ef | grep chronyd | grep -v grep chrony 768 1 0 14:52 ? 00:00:00 /usr/sbin/chronyd -F 2 ``` - CentOS 7 - Rocky Linux 8 - NAVIX 9, Rocky Linux 9 2. Check the NTP settings of NAVER Cloud Platform received from DHCP. The IPs of the NTP server provided in the VPC environment are `169.254.169.123` and `169.254.169.124`. ``` [root@rockylinux8 ~]# cat /var/lib/dhclient/chrony.servers.eth0 169.254.169.123 iburst 169.254.169.124 iburst ``` ``` [root@naivx9 ~]# cat /run/chrony-dhcp/eth0.sources server 169.254.169.123 iburst server 169.254.169.124 iburst server 169.254.169.123 iburst server 169.254.169.124 iburst ``` If the file does not contain `169.254.169.123` and `169.254.169.124`, you can add the NTP settings directly to proceed as follows: ``` [root@naivx9 ~]# cat /etc/chrony.conf # Use public servers from the pool.ntp.org project. # Please consider joining the pool (https://www.pool.ntp.org/join.html). pool navix.pool.ntp.org iburst ... Omitted ... [root@naivx9 ~]# systemctl restart chronyd.service [root@naivx9 ~]# chronyc -n sources MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? 121.174.142.82 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 175.195.167.194 0 7 0 - +0ns[ +0ns] +/- 0ns ^* 169.254.169.123 2 6 17 17 +11us[ +185us] +/- 1472us ^+ 169.254.169.124 2 6 17 17 +35us[ +208us] +/- 1447us ``` - CentOS 7, Rocky Linux 8 - NAVIX 9, Rocky Linux 9 3. Check whether time has been synchronized using the `timedatectl` command. If the `NTP synchronized` value or `System clock synchronized` value is `yes`, time has been synchronized successfully. ``` [root@centos7 ~]# timedatectl Local time: Fri 2023-08-18 13:57:57 KST Universal time: Fri 2023-08-18 04:57:57 UTC RTC time: Fri 2023-08-18 04:57:57 Time zone: Asia/Seoul (KST, +0900) NTP enabled: yes NTP synchronized: yes RTC in local TZ: no ``` ``` [root@navix9 ~]# timedatectl Local time: Thu 2025-06-26 18:52:51 KST Universal time: Thu 2025-06-26 09:52:51 UTC RTC time: Thu 2025-06-26 09:52:51 Time zone: Asia/Seoul (KST, +0900) System clock synchronized: yes NTP service: active RTC in local TZ: no ``` - CentOS 7 - NAVIX 9, Rocky Linux 8, Rocky Linux 9 4. Check the settings and content of the /etc/chrony.conf file. Change the settings of this file to add new time synchronization settings or change the existing settings. The IPs of the NTP server provided in the VPC environment are `169.254.169.123` and `169.254.169.124`. ``` [root@centos7 ~]# cat /etc/chrony.conf # Use public servers from the pool.ntp.org project. server 0.centos.pool.ntp.org iburst server 1.centos.pool.ntp.org iburst server 2.centos.pool.ntp.org iburst server 3.centos.pool.ntp.org iburst ... Omitted ... ``` ``` [root@rockylinux8 ~]# cat /etc/chrony.conf # Use public servers from the pool.ntp.org project. # Please consider joining the pool (http://www.pool.ntp.org/join.html). pool 2.rocky.pool.ntp.org iburst ... Omitted ... ``` ``` [root@navix9 ~]# cat /etc/chrony.conf # Use public servers from the pool.ntp.org project. # Please consider joining the pool (https://www.pool.ntp.org/join.html). pool navix.pool.ntp.org iburst ... Omitted ... ``` - CentOS 7 - Rocky Linux 8 - NAVIX 9, Rocky Linux 9 5. Check the time synchronization content. ``` [root@navix9 ~]# chronyc -n sources -v .-- Source mode '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current best, '+' = combined, '-' = not combined, | / 'x' = may be in error, '~' = too variable, '?' = unusable. || .- xxxx [ yyyy ] +/- zzzz || Reachability register (octal) -. | xxxx = adjusted offset, || Log2(Polling interval) --. | | yyyy = measured offset, || \ | | zzzz = estimated error. || | | \ MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? 175.195.167.194 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 158.247.202.103 0 10 0 - +0ns[ +0ns] +/- 0ns ^? 194.0.5.123 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 193.123.243.2 0 10 0 - +0ns[ +0ns] +/- 0ns ^? 175.210.18.47 0 10 0 - +0ns[ +0ns] +/- 0ns ^? 121.174.142.81 0 10 0 - +0ns[ +0ns] +/- 0ns ^? 121.174.142.82 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 203.32.26.46 0 9 0 - +0ns[ +0ns] +/- 0ns ^+ 169.254.169.123 2 9 377 333 +859us[ +861us] +/- 2367us ^* 169.254.169.124 2 8 377 147 +1003us[+1005us] +/- 2174us ``` ## Ubuntu Inspect the NTP settings and file on your Ubuntu OS provided on NAVER Cloud Platform. Note The following guide applies to Ubuntu 18.04 to Ubuntu 24.04. 1. Check the status of the systemd-timesyncd daemon. If the systemd-timesyncd daemon is enabled, chronyd cannot be started upon booting. ``` root@ubuntu1804:~# systemctl is-enabled systemd-timesyncd.service enabled root@ubuntu1804:~# systemctl disable systemd-timesyncd Removed /etc/systemd/system/sysinit.target.wants/systemd-timesyncd.service. root@ubuntu1804:~# systemctl stop systemd-timesyncd root@ubuntu1804:~# systemctl restart chronyd root@ubuntu1804:~# systemctl is-enabled systemd-timesyncd.service disabled ``` ``` root@ubuntu2204:~# systemctl is-enabled systemd-timesyncd.service masked ``` ``` root@ubuntu2404:~# systemctl list-unit-files | grep systemd-timesyncd | wc -l 0 ``` - Ubuntu 18.04 On Ubuntu 18.04, systemd-timesynd.service is `enabled`. To use the chronyd service normally, change to `disabled` status. - Ubuntu 20.04 ~ 22.04 - Ubuntu 24.04 By default, Ubuntu 24.04 does not have the systemd-timesyncd package installed. 2. Check whether chrony is installed and running. ``` root@ubuntu2404:~# dpkg -l | grep chrony ii chrony 4.5-1ubuntu4.2 amd64 Versatile implementation of the Network Time Protocol root@ubuntu2404:~# ps -ef | grep chronyd | grep -v grep _chrony 734 1 0 14:52 ? 00:00:00 /usr/sbin/chronyd -F 1 _chrony 737 734 0 14:52 ? 00:00:00 /usr/sbin/chronyd -F 1 ``` 3. Check the NTP settings of NAVER Cloud Platform received from DHCP. The IPs of the NTP server provided in the VPC environment are `169.254.169.123` and `169.254.169.124`. ``` root@ubuntu2004:~# cat /var/lib/dhcp/chrony.servers.eth0 169.254.169.123 iburst 169.254.169.124 iburst ``` ``` root@ubuntu2404:~# cat /run/chrony-dhcp/eth0.sources server 169.254.169.123 iburst server 169.254.169.124 iburst ``` If 169.254.169.123 and 169.254.169.124 don't exist in the corresponding file, you can proceed as follows: ``` root@ubuntu2404:~# cat /etc/chrony/chrony.conf ... Omitted ... # See http://www.pool.ntp.org/join.html for more information. pool ntp.ubuntu.com iburst maxsources 4 pool 0.ubuntu.pool.ntp.org iburst maxsources 1 pool 1.ubuntu.pool.ntp.org iburst maxsources 1 pool 2.ubuntu.pool.ntp.org iburst maxsources 2 server 169.254.169.123 iburst server 169.254.169.124 iburst ... Omitted ... root@ubuntu2404:~# systemctl restart chronyd.service root@ubuntu2404:~# chronyc -n sources MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? 91.189.91.157 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 185.125.190.58 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 185.125.190.56 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 185.125.190.57 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 194.0.5.123 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 193.123.243.2 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 175.195.167.194 0 7 0 - +0ns[ +0ns] +/- 0ns ^? 121.174.142.81 0 7 0 - +0ns[ +0ns] +/- 0ns ^* 169.254.169.123 2 6 17 6 +7981ns[ +255ns] +/- 1530us ^+ 169.254.169.124 2 6 17 7 -550ns[-8276ns] +/- 1546us ``` - Ubuntu 18.04 ~ 20.04 - Ubuntu 22.04 ~ 24.04 4. Check whether time has been synchronized using the `timedatectl` command. If the `System clock synchronized` value is `yes`, time has been synchronized successfully. - Ubuntu 18.04 ``` root@ubuntu1804:~# timedatectl Local time: Wed 2023-08-18 19:33:52 KST Universal time: Wed 2023-08-18 10:33:52 UTC RTC time: Wed 2023-08-18 10:33:53 Time zone: Asia/Seoul (KST, +0900) System clock synchronized: yes systemd-timesyncd.service active: no RTC in local TZ: no ``` - Ubuntu 20.04 ~ 24.04 ``` root@ubuntu2404:~# timedatectl Local time: Fri 2025-07-04 15:17:54 KST Universal time: Fri 2025-07-04 06:17:54 UTC RTC time: Fri 2025-07-04 06:17:54 Time zone: Asia/Seoul (KST, +0900) System clock synchronized: no NTP service: active RTC in local TZ: no ``` 5. Check the settings and content of the /etc/chrony/chrony.conf file. Change the settings of this file to add new time synchronization settings or change the existing settings. The IPs of the NTP server provided in the VPC environment are `169.254.169.123` and `169.254.169.124`. ``` root@ubuntu2404:~# cat /etc/chrony/chrony.conf # See http://www.pool.ntp.org/join.html for more information. pool ntp.ubuntu.com iburst maxsources 4 pool 0.ubuntu.pool.ntp.org iburst maxsources 1 pool 1.ubuntu.pool.ntp.org iburst maxsources 1 pool 2.ubuntu.pool.ntp.org iburst maxsources 2 ... Omitted ... ``` 6. Check the time synchronization content. ``` root@ubuntu2404:~# chronyc -n sources -v .-- Source mode '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current best, '+' = combined, '-' = not combined, | / 'x' = may be in error, '~' = too variable, '?' = unusable. || .- xxxx [ yyyy ] +/- zzzz || Reachability register (octal) -. | xxxx = adjusted offset, || Log2(Polling interval) --. | | yyyy = measured offset, || \ | | zzzz = estimated error. || | | \ MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? 185.125.190.57 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 185.125.190.58 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 185.125.190.56 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 91.189.91.157 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 158.247.202.103 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 194.0.5.123 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 121.174.142.82 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 121.174.142.81 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 203.32.26.46 0 9 0 - +0ns[ +0ns] +/- 0ns ^? 175.195.167.194 0 9 0 - +0ns[ +0ns] +/- 0ns ^+ 169.254.169.123 2 7 377 201 +128us[ +128us] +/- 1573us ^* 169.254.169.124 2 9 377 256 +946us[ +932us] +/- 2307us ``` Note It has been found that NTP server settings provided via DHCP are not being applied on Ubuntu 24.04. This may cause time differences in environments where external communication is not possible (no public IP or no NAT configuration). This issue does not occur in environments with a public IP or NAT configuration, as it synchronizes normally with an external public time server. This issue has been confirmed to be an internal bug in the Ubuntu 24.04 OS, and an edited BaseOS image is scheduled for release according to the following timeline: - BaseOS image applied on November 20, 2025 ※ Date may be subject to change depending on internal circumstances. For Ubuntu 24.04 VMs that are already in use and cannot communicate externally (no public IP or NAT configuration), you may take the following actions: ``` root@ubuntu2404:~# chronyc -n sources -v | grep -e 169.254.169.123 -e 169.254.169.124 root@ubuntu2404:~# root@ubuntu2404:~# echo -e "server 169.254.169.123 iburst\nserver 169.254.169.124 iburst" >/etc/chrony/sources.d/navercloud-ntp-server.sources root@ubuntu2404:~# cat /etc/chrony/sources.d/navercloud-ntp-server.sources server 169.254.169.123 iburst server 169.254.169.124 iburst root@ubuntu2404:~# systemctl restart chronyd root@ubuntu2404:~# chronyc -n sources -v | grep -e 169.254.169.123 -e 169.254.169.124 ^- 169.254.169.123 2 6 17 0 +28us[ +28us] +/- 1460us ^* 169.254.169.124 2 6 7 1 +1923ns[-4830ns] +/- 1613us ``` ## NTP FAQs ### Q: Do I only need to set up 2 NTP servers provided by NAVER Cloud for time synchronization through the network? NAVER Cloud provides NTP servers for free, considering the diverse environments used by customers. If your network environment enables external access through NAT or public IP, it is recommended to set up at least 3 external public NTP servers in addition to NAVER Cloud NTP servers. If you set up only 2 NTP servers and synchronization fails on 1 of the 2 servers, it may lead to a majority problem where it becomes unclear which server is providing the accurate time. The official NTP configuration guide also recommends a minimum of 3 servers and 5 servers in general. For more information, see [Official website](https://www.ntppool.org/en/join/configuration.html). If your private subnet without the NAT settings blocks access to the external network, it is recommended to set up at least 3 NTP servers, including a Bastion server configured to synchronize with external public NTP servers.