Check time sync settings
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Check time sync settings
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Available in VPC
NAVER Cloud Platform provides an NTP server for time synchronization. Time sync settings have significant effects on system operation and management and are closely related to security, network communication, data accuracy, etc. It is recommended to use a daemon that synchronizes the time continuously rather than performs one-time synchronization periodically.
CentOS, Rocky Linux
Inspect the NTP settings and file in the RedHat OS provided on NAVER Cloud Platform.
Note
Described for CentOS 7 and Rocky Linux 8.
Check whether chrony is installed and running.
- CentOS 7
[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 - Rocky Linux 8
[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
- CentOS 7
Check the NTP settings of NAVER Cloud Platform received from DHCP. The IPs of the NTP server provided in the VPC environment are
169.254.169.123and169.254.169.124.[root@centos7 ~]# cat /var/lib/dhclient/chrony.servers.eth0 169.254.169.123 iburst 169.254.169.124 iburst- If the directory does not contain
169.254.169.123and169.254.169.124, you can add the NTP settings yourself as follows:[root@centos7 ~]# 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). #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 server 169.254.169.123 server 169.254.169.124 ... Omitted... [root@centos7 ~]# systemctl restart chronyd.service [root@centos7 ~]# chronyc sources 210 Number of sources = 2 MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? 169.254.169.123 3 6 3 6 -1689us[-1689us] +/- 48ms ^? 169.254.169.124 3 6 3 6 -1437us[-1437us] +/- 38ms
- If the directory does not contain
Check whether time has been synchronized using the
timedatectlcommand.- If the
NTP synchronizedvalue orSystem clock synchronizedvalue isyes, time has been synchronized successfully. - CentOS 7
[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 - Rocky Linux 8
[root@rockylinux8 ~]# 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) System clock synchronized: yes NTP service: active RTC in local TZ: no
- If the
Check the settings and content of the
/etc/chrony.conffile. Change the settings of this file to add new time sync settings or change the existing settings.- The IPs of the NTP server provided in the VPC environment are
169.254.169.123and169.254.169.124. - CentOS 7
[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... - Rocky Linux 8
- In the time sync settings, annotate the incorrectly inserted 10.X IP band.
- Since server information for time synchronization is received from the DHCP server, time synchronization is not affected even if you do not make this change.
- Before annotation
[root@rockylinux8 ~]# cat /etc/chrony.conf # These servers were defined in the installation: server 10.22.64.22 iburst server 10.22.64.38 iburst # Use public servers from the pool.ntp.org project. # Please consider joining the pool (http://www.pool.ntp.org/join.html). ... Omitted... - After annotation
[root@rockylinux8 ~]# cat /etc/chrony.conf # These servers were defined in the installation: # server 10.22.64.22 iburst # server 10.22.64.38 iburst # Use public servers from the pool.ntp.org project. # Please consider joining the pool (http://www.pool.ntp.org/join.html). server 169.254.169.123 server 169.254.169.124 ... Omitted...
- The IPs of the NTP server provided in the VPC environment are
Check the time sync content.
[root@centos7 ~]# systemctl restart chronyd.service [root@centos7 ~]# chronyc sources -v .-- Source mode '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current synced, '+' = combined , '-' = not combined, | / '?' = unreachable, 'x' = time may be in error, '~' = time too variable. || .- 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 =============================================================================== ^+ 169.254.169.123 3 6 377 14 +3999us[+3999us] +/- 227ms ^+ 169.254.169.124 3 6 377 51 +198us[ +198us] +/- 44ms
Ubuntu
Inspect the NTP settings and file in your Ubuntu OS provided on NAVER Cloud Platform.
Note
Described for Ubuntu 18.04 and Ubuntu 20.04.
Check the status of systemd-timesyncd daemon.
- If systemd-timesyncd daemon is enabled, the chronyd service does not operate upon booting. Make sure to disable the daemon.
- Ubuntu 18.04: systemd-timesynd.service is enabled by default. To use the chronyd service normally, disable this setting.
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- Ubuntu 20.04
root@ubuntu2004:~# systemctl is-enabled systemd-timesyncd.service masked
Check whether chrony is installed and running.
- Ubuntu 18.04
root@ubuntu1804:~# dpkg -l | grep chrony ii chrony 3.2-4ubuntu4.5 amd64 Versatile implementation of the Network Time Protocol root@ubuntu1804:~# ps -ef | grep chronyd | grep -v grep _chrony 2149 1 0 19:27 ? 00:00:00 /usr/sbin/chronyd - Ubuntu 20.04
root@ubuntu2004:~# dpkg -l | grep chrony ii chrony 3.5-6ubuntu6.2 amd64 Versatile implementation of the Network Time Protocol root@ubuntu2004:~# ps -ef | grep chronyd | grep -v grep _chrony 680 1 0 17:48 ? 00:00:00 /usr/sbin/chronyd -F -1 _chrony 683 680 0 17:48 ? 00:00:00 /usr/sbin/chronyd -F -1
- Ubuntu 18.04
Check the NTP settings of NAVER Cloud Platform received from DHCP. The IPs of the NTP server provided in the VPC environment are
169.254.169.123and169.254.169.124.root@ubuntu2004:~# cat /var/lib/dhcp/chrony.servers.eth0 169.254.169.123 iburst 169.254.169.124 iburst- If the directory does not contain
169.254.169.123and169.254.169.124, you can add the NTP settings yourself as follows:root@ubuntu2004:~# 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 server 169.254.169.123 server 169.254.169.124 ... Omitted... root@ubuntu2004:~# systemctl restart chronyd.service root@ubuntu2004:~# chronyc sources 210 Number of sources = 2 MS Name/IP address Stratum Poll Reach LastRx Last sample =============================================================================== ^? 169.254.169.123 3 6 1 8 +608us[ +608us] +/- 19ms ^? 169.254.169.124 3 6 1 8 +669us[ +669us] +/- 20ms
- If the directory does not contain
Check whether time has been synchronized using the
timedatectlcommand.- If the value
System clock synchronizedvalue isyes, 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
root@ubuntu2004:~# timedatectl Local time: Wed 2023-08-18 17:40:33 KST Universal time: Wed 2023-08-18 08:40:33 UTC RTC time: Wed 2023-08-18 08:40:34 Time zone: Asia/Seoul (KST, +0900) System clock synchronized: yes NTP service: active RTC in local TZ: no
- If the value
Check the settings and content of the
/etc/chrony/chrony.conffile. Change the settings of this file to add new time sync settings or change the existing settings.- The IPs of the NTP server provided in the VPC environment are
169.254.169.123and169.254.169.124.root@ubuntu2004:~# cat /etc/chrony/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...
- The IPs of the NTP server provided in the VPC environment are
Check the time sync content.
root@ubuntu2004:~# chronyc sources -v .-- Source mode '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current synced, '+' = combined , '-' = not combined, | / '?' = unreachable, 'x' = time may be in error, '~' = time too variable. || .- 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 =============================================================================== ^+ 169.254.169.123 3 6 377 14 +3999us[+3999us] +/- 227ms ^+ 169.254.169.124 3 6 377 51 +198us[ +198us] +/- 44ms
FAQ related to NTP
Q: Do I only need to set up two NTP servers provided by NAVER Cloud for time synchronization via network?
NAVER Cloud provides NTP servers for free, considering the diverse environments used by customers.
If your network environment enables external access via NAT or public IP, it is recommended to set up at least three external public NTP servers in addition to NAVER Cloud NTP servers.
If you set up only two NTP servers and synchronization fails on one of them, 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 three servers and five servers in general. For more information, see Official website.
If your private subnet without the NAT settings blocks access to the external network, it is recommended to set up at least three NTP servers, including a Bastion server configured to synchronize with external public NTP servers.
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