Business Software Applications

Summary about Leap Second and Linux freeze

If your organization run multiple Linux servers; or if you use cloud services from external vendors; you may have noticed a glitch or issue around June 30 to July 1; and those are related to the now famous "Leap Second" issue.

Many IT organizations and cloud service vendors use/adopt Linux Operating System because of course it uses the model of free and open-source software development and distribution. But as anything in live; free comes with a price. Although there are also organizations that provide consulting services for Linux; much of the Linux installation base is left to the developers; and not necessarily they want to tell their managers to pay for those Linux consulting services.

Anyhow... going back to "Leap Second"; if you search the Internet you may find various articles about the fact that the time on Earth is slowing down; and that because time is slowing down; every now and then we need to adjust the "Civil Time" - basically the time under which our computers are running. Or the time by which your boss may know you are late for a meeting.

This time correction is actually 1 second; the "Leap Second"; and to correct such time; a leap second was inserted at the end of June 30, 2015 at 23:59:60 UTC.

But how that second gets introduced in our lives; in our computers? Well high level summary is = most Internet servers must remain in sync in order to exchange data reliable; as such they use the Network Time Protocol (NTP); this is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. But for multiple organizations can not reliable interconnect unless there is a define set of NTP servers from which they can sync from time to time. This is sometimes know as Time Servers - for more info you can visit

Back to our subject: In 30 June, the Network Time Protocol (NTP) daemon scheduled a leap second to occur at midnight, meaning that the final minute of the day was 61 seconds long... But from Linux point of view, the last second of June 30th will repeat itself as another second...

What? So in essence you have this:

2015-06-30 23:59:59 Local Time
2015-06-30 23:59:60 Leap Second
2015-07-01 00:00:00 Local Time

Your Linux server gets NTP telling this = 23:59:60 => then it cannot consume such information; and pretty much it goes crazy. What is the impact? well that will depend on your set up, your Linux OS version, etc. But in essence Linux can freeze or it can just be unable to process; or think that it has already process data in the past (1 second). At this point; the only possible alternative is probably to "reboot" your server; so you basically reset it - and have it sync automatically. Then your server will forget of the 23:59:60 and live goes on.

When will the next Leap Second come and how will it affect Linux is still unknown; but the best strategy is to update to the latest Linux version or the latest Linux distribution you use; and have your developers exchange with other developers to understand the future impact.

Posted on July 08, 2015