Systat (protocol)

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Systat or Active Users is a simple Internet protocol ostensibly useful for "debugging and measurement".[1] A connection to port 11, by either TCP or UDP, elicits a list of users currently logged into the system. Though it remains an official Internet protocol, its use is considered a security vulnerability.[2]


  1. ^ Postel, J. (May 1983). Active Users. IETF. doi:10.17487/RFC0866. RFC 866.
  2. ^ "systat and netstat". eTutorials.