Taken from Resolve Leap Second Issues in Red Hat Enterprise Linux
Leap seconds are a periodic one-second adjustment of Coordinated Universal Time(UTC) in order to keep a system's time of day close to the mean solar time. However, the Earth's rotation speed varies in response to climatic and geological events, and due to this, UTC leap seconds are irregularly spaced and unpredictable.
Upcoming Leap Second Events:
The next leap second will occur on 2016 December 31, 23h 59m 60s UTC.
Red Hat Enterprise Linux versions 4
Red Hat Enterprise Linux versions 5
Red Hat Enterprise Linux versions 6
Red Hat Enterprise Linux versions 7
Customers running highly time-sensitive or un-patched RHEL servers.
The severity depends on how far behind the customer in on updating RHEL and how sensitive their operations are to time adjustments. Some customers will just appreciate the news. Others running un-patched servers may experience kernel hangs.
Another leap second will be added on December 31, 2016.
Customers running RHEL servers that are completely patched and running NTP should not be concerned. (Applications should be fine, too, but it is always best to check with one's vendors.)
Customers running completely patched RHEL servers but not NTP will find their systems' times off by 1 second. Customers will need to manually correct that.
Customers running un-patched servers that cannot update their kernel, ntp and tzdata packages to at least the latest versions listed in the below document's "Known Issues" section's links should contact our Support Center for further assistance.
Resolve Leap Second Issues in Red Hat Enterprise Linux: https://access.redhat.com/articles/15145#event