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Leap-second handling on NSM

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This article describes the leap-second bug and possible workarounds on NSM appliances.

This will only occur if NTP is enabled.


How to configure or adjust the NSM appliances against the NTP leap second, which can cause the system to hang.

What is a leap second?

A leap second is a one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) so as to keep its time of day close to the mean solar time. A leap second is inserted or deleted in the UTC time scale on the last day of June or December.

For more information about leap second, see


After a leap second has been inserted, the system can hang as certain Linux kernels (versions before 2.6.29) have issues handling leap seconds to the point where it can cause a kernel panic.


Systems not running NTP

Linux or CentOS systems not using NTP to synchronize their timekeeping will not correct for leap seconds and will not be impacted by this bug.

The time reported by these systems will have a one-second difference relative to UTC after the leap-second correction.

You should reset the clock manually after leap seconds occur.

Systems running NTP

Systems running NTP will recieve a leap-second correction.

Unpatched systems might experience a kernel hang or crash.

You have two options:

1. Patch the system (recommended)

NSM appliance:

Note: Package from CentOS website
Upgrade the tzdata package on CentOS5 to tzdata-2015a-1.el5, and CentOS6 to tzdata-2015a-1.el6

For CentOS5, tzdata-2015a-1.el5, see
For CentOS6, tzdata-2015a-1.el6, see

If you are running CentOS version 4, Upgrade to CentOS 5 or 6.

Note: you must be a root user to run this command.

To install an rpm, you need to use following command:

# rpm -Uvh <package name>

Your Red Hat server:

Please contact Red Hat for updated package.

2. Disable NTP

Note: Even if you chose to stop the NTP service during the leap second and start it after the leap second, we recommend upgrading the tzdata package.

Note: Previously provided slew mode was not QAed and is not recommended.

References from Red Hat:

To clear the leap-second insertion flag after it has been received, see

To resolve leap-second issues in Red Hat Enterprise Linux, see

Related Links: