node_exporter/vendor/github.com/beevik/ntp/README.md

ntp

The ntp package is an implementation of a Simple NTP (SNTP) client based on RFC5905. It allows you to connect to a remote NTP server and request information about the current time.

Querying the current time

If all you care about is the current time according to a remote NTP server, simply use the Time function:

time, err := ntp.Time("0.beevik-ntp.pool.ntp.org")

Querying time metadata

To obtain the current time as well as some additional metadata about the time, use the Query function:

response, err := ntp.Query("0.beevik-ntp.pool.ntp.org")
time := time.Now().Add(response.ClockOffset)

Alternatively, use the QueryWithOptions function if you want to change the default behavior used by the Query function:

options := ntp.QueryOptions{ Timeout: 30*time.Second, TTL: 5 }
response, err := ntp.QueryWithOptions("0.beevik-ntp.pool.ntp.org", options)
time := time.Now().Add(response.ClockOffset)

The Response structure returned by Query includes the following information:

• Time: The time the server transmitted its response, according to its own clock.
• ClockOffset: The estimated offset of the local system clock relative to the server's clock. For a more accurate time reading, you may add this offset to any subsequent system clock reading.
• RTT: An estimate of the round-trip-time delay between the client and the server.
• Precision: The precision of the server's clock reading.
• Stratum: The server's stratum, which indicates the number of hops from the server to the reference clock. A stratum 1 server is directly attached to the reference clock. If the stratum is zero, the server has responded with the "kiss of death".
• ReferenceID: A unique identifier for the consulted reference clock.
• ReferenceTime: The time at which the server last updated its local clock setting.
• RootDelay: The server's aggregate round-trip-time delay to the stratum 1 server.
• RootDispersion: The server's estimated maximum measurement error relative to the reference clock.
• RootDistance: An estimate of the root synchronization distance between the client and the stratum 1 server.
• Leap: The leap second indicator, indicating whether a second should be added to or removed from the current month's last minute.
• MinError: A lower bound on the clock error between the client and the server.
• KissCode: A 4-character string describing the reason for a "kiss of death" response (stratum=0).
• Poll: The maximum polling interval between successive messages to the server.

The Response structure's Validate method performs additional sanity checks to determine whether the response is suitable for time synchronization purposes.

err := response.Validate()
if err == nil {
    // response data is suitable for synchronization purposes
}

Using the NTP pool

The NTP pool is a shared resource used by people all over the world. To prevent it from becoming overloaded, please avoid querying the standard pool.ntp.org zone names in your applications. Instead, consider requesting your own vendor zone or joining the pool.