<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> </head> <body bgcolor="#ffffff" text="#000000"> Hi, I've been using check_ntp_time plugin to check the time offset of all my time servers. It's been working perfectly for a while. Last night (29 to 30/12 at 00:00), all the checks start having the same behavior quite at the same time. All of them return : " NTP CRITICAL: Offset unknown" Of course, all the time servers are running, and their time is accurate. I can't understand why all the checks start failing all at the same time. Here's an example output below. Thank you in advance for any advice. Kind regards <div class="moz-signature">-- <title>Signature</title> <meta http-equiv="Content-Type" content="text/html; "> <style type="text/css">  </style> Toussaint OTTAVI MEDI INFORMATIQUE Mail: <a class="moz-txt-link-abbreviated" href="mailto:t.ottavi@medi.fr">t.ottavi@medi.fr</a> </div> serveurlinux:/usr/lib/nagios/plugins # check_ntp_time -H 10.0.0.4 -v sending request to peer 0 response from peer 0: offset 0.3197530025 sending request to peer 0 response from peer 0: offset 0.3188920024 sending request to peer 0 response from peer 0: offset 0.3346090025 sending request to peer 0 response from peer 0: offset 0.3337990025 discarding peer id 0: flags=1 overall average offset: 0 NTP CRITICAL: Offset unknown| serveurlinux:/usr/lib/nagios/plugins # check_ntp_time -H ntp2.usno.navy.mil -v sending request to peer 0 response from peer 0: offset 0.0600928269 sending request to peer 0 response from peer 0: offset 0.06049711903 sending request to peer 0 re-sending request to peer 0 response from peer 0: offset 0.06112928403 sending request to peer 0 response from peer 0: offset 0.05989775999 discarding peer id 0: flags=1 overall average offset: 0 NTP CRITICAL: Offset unknown| </body> </html>