Several reasons could cause this duplication of log entries:
Multiple Terminals or Connections: Users might be logging in from different terminals or connections simultaneously, resulting in multiple log entries with the same timestamp.
Logging Mechanism: The logging mechanism itself may generate duplicate log entries under specific conditions. This can happen if the system writes the log entry and, for some reason, retries the process, resulting in identical entries.
Log Rotation and Aggregation: Some log rotation or aggregation processes might temporarily duplicate log entries as they handle and process logs across different files or systems.
Logging Configuration: The logging configuration on the system may have specific settings that lead to duplicate log entries for certain events.
To further investigate and understand why there are duplicate entries in the auth.log, you may want to check the specific logging configuration, explore the system’s login history, and review any recent changes that might have impacted the logging mechanism. It’s also a good idea to monitor the log entries over time to see if this is a recurring issue or just an isolated event.