Quick and straight forward update that a lot of users will probably look over. It is Cisco Bug CSCut25356 – The Leap Second. Basically it involves Cisco Unified Communications Manager (CallManager) versions 7.0, 7.1, and 8.0 configurations that use NTP. Over time there will be things called lead seconds, where time will basically “jump” ahead one second to remain precise. If your CallManager system is running NTP on June 30th, 2015 when this occurs, then your system might be subject to kernel halts and or other system instability.
So what do you do? That’s the pretty easy part. The workaround is to simply disable NTP at least 24 hours prior to June 30th, 2015. Then once June 30th passes and the leap second is passed in terms of your NTP server, you can safely re-enable this option.
Nothing too much to be worried about as long as you are proactive and take care of this small issue!