Clock not publishing?

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No, it's not abnormal. The /clock topic is only used if you are not using the wall clock. For example, if you are using a simulation then the /clock topic is published to provide the simulated world time, because it is often different from the real world time. This allows nodes to execute at the same pace as the simulation.

When using hardware distributed on the network, and not using not simulation or log files (i.e. when /clock is empty), to make sure everything in your system uses the same time you must use a tool such as NTP to keep all system clocks synced.