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docs/advanced/ntp.md

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+# NTP synchronization
+
+The Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems. Time synchronization is important to Kubernetes and Etcd.
+
+## Enable the NTP
+
+To start the ntpd(or chrony) service and enable it at system boot. There are related specific variables:
+
+```ShellSession
+ntp_enabled: true
+```
+
+The NTP service would be enabled and sync time automatically.
+
+## Customize the NTP configure file
+
+In the Air-Gap environment, the node cannot access the NTP server by internet. So the node can use the customized ntp server by configuring ntp file.
+
+```ShellSession
+ntp_enabled: true
+ntp_manage_config: true
+ntp_servers:
+  - "0.your-ntp-server.org iburst"
+  - "1.your-ntp-server.org iburst"
+  - "2.your-ntp-server.org iburst"
+  - "3.your-ntp-server.org iburst"
+```
+
+## Setting the TimeZone
+
+The timezone can also be set by the `ntp_timezone` , eg: "Etc/UTC","Asia/Shanghai". If not set, the timezone will not change.
+
+```ShellSession
+ntp_enabled: true
+ntp_timezone: Etc/UTC
+```
+
+## Advanced Configure
+
+Enable `tinker panic` is useful when running NTP in a VM environment to avoiding clock drift on VMs. It only takes effect when ntp_manage_config is true.
+
+```ShellSession
+ntp_tinker_panic: true
+```
+
+Force sync time immediately by NTP after the ntp installed, which is useful in newly installed system.
+
+```ShellSession
+ntp_force_sync_immediately: true
+```