How to Use the Command 'sntpd' (with Examples)

The sntpd command is an SNTP (Simple Network Time Protocol) server that synchronizes the local system clock with a remote server. Unlike full-featured NTP servers, SNTP provides limited functionality and is suitable for environments where precise clock synchronization is not critical. It is generally used as a lightweight alternative to ensure that networked devices have a reasonably accurate time without the overhead of running a full NTP daemon. Although sntpd is typically run as a daemon to continually adjust the clock, it can be invoked with specific options to suit particular use cases, but it should not be run manually under typical circumstances.

Use case 1: Start the daemon

Code:

sntpd

Motivation:
Starting the sntpd daemon involves running it in the background as a service. This is useful when you want your system’s time to be consistently synchronized with a remote SNTP server. By maintaining an accurate system time, you ensure that time-dependent processes work correctly, system logs are accurate, and the coordination with distributed systems is maintained.

Explanation:
The command sntpd is executed without any arguments here, which means it starts the daemon with its default configuration. In its default mode, sntpd will continuously listen for SNTP requests and handle network time synchronization autonomously. This ensures the local clock consistently aligns with a remote time source.

Example output:
As the sntpd service is generally run in the background, there will be no immediate terminal output. However, you may check system logs or process lists to confirm that the service is running correctly.

Use case 2: Overwrite existing state with the local clock (stratum 1)

Code:

sntpd -L

Motivation:
Configuring a machine as a primary time server (stratum 1) is important when you want it to be a time authority within a local network, especially in environments isolated from external time sources. This mode allows the local clock to be used as the reference time, providing a stratum 1 service, which is considered authoritative.

Explanation:
The -L option tells sntpd to use the local clock to initialize its time state, essentially making the local machine a master or primary time server. A stratum 1 server typically synchronizes to a high precision external time source (like radio clocks, or GPS), but in this case, it serves from an internal clock without such references, which means it should be used when accurate absolute time is less critical.

Example output:
As sntpd operates as a service, there’s usually no direct output. You can verify the service’s activity through logging systems or status commands, which may indicate that the server is running and serving time based on the local clock.

Use case 3: Use a custom file for the SNTP state

Code:

sntpd -z path/to/state.bin

Motivation:
For environments where state persistence across restarts is critical, using a custom file for the SNTP state can ensure that previous time state information is retained. This can be important for systems that expect to maintain continuity in time-keeping data even after rebooting or restarting services.

Explanation:
The -z path/to/state.bin option specifies a custom file path where sntpd will read from and store its current state information. This helps in retaining time state across various operational cycles. Such a feature is crucial in environments where clock state consistency must be maintained without re-synchronizing from scratch every time the daemon starts.

Example output:
This command will not show any immediate terminal output, but you can investigate the specified file (path/to/state.bin) to confirm that it is being used by the sntpd for managing its state. Logs or system diagnostics might show that the state information is being read or written as anticipated.

Conclusion:

The sntpd command provides a simplified means of running a time service on Unix-based systems, delivering core time synchronization functionality without the complexity of a full NTP implementation. Whether running as a basic daemon, setting up a stratum 1 server, or managing state across restarts, sntpd can be adjusted to fit various needs. Each use case demonstrates how specific options of sntpd can be employed to achieve precise objectives, maintaining time accuracy within network environments under different conditions.