Red Hat patches for the Leap Second

There will be a leap second June 30 2015 at midnight UCT. FSMLabs has tested TimeKeeper on Red Hat Linux and found that TimeKeeper handles the leap second properly.

TimeKeeper avoids using the mechanism for managing the leap second that is sometimes built into Linux. By default TimeKeeper “slews” on the leap second to allow a gradual resynchronization over a few minutes. This “slew” cushions the effect of the Leap Second on applications and insures that time does not go backwards.

The Linux component that compensates for the leap second is quite complex and has a history of causing system crashes.

Using TimeKeeper means that you don’t have to worry about the following issues (the following text is copied directly from Redhat’s note: Resolve Leap Second Issues in Red Hat Enterprise Linux. Emphasis is added.


Known Issues

RHEL 4

There is a chance that the printing of this message can cause the kernel to crash in Red Hat Enterprise Linux 4; this issue is documented in System hangs on printing the leap second insertion message.

Ensure that tzdata-2015a-1.el4 or later is installed so that this leap second may be inserted for systems not synchronized by ntpd; this package was released from RHEA-2015:0141-1.

RHEL 5

There is a chance that the printing of this message can cause the kernel to crash in Red Hat Enterprise Linux 5; this issue is documented in System hangs on printing the leap second insertion message.

Ensure that tzdata-2015a-1.el5 or later is installed so that this leap second may be inserted for systems not synchronized by ntpd; this package was released from RHEA-2015:0141-1.

RHEL 6

There is a chance that a system can hang once it receives notification of the insertion of a leap second; this issue is documented in Systems hang due to leap-second livelock.

After the leap second has been inserted futex heavy applications began consuming a large amount of CPU; this issue is documented in Why is there high CPU usage after inserting the leap second?.

Ensure that tzdata-2015a-1.el6 or later is installed so that this leap second may be inserted for systems not synchronized by ntpd; this package was released from RHEA-2015:0141-1.

The TAI offset is not updated correctly during the leap second; this issue is documented in TAI offset is incorrect during the leap second.

Using -x with ntp still results in instantaneous clock changes when leap second occurs; this issue is documented in Does Red Hat plan to release xleap.patch with ntp?.

RHEL 7

Ensure that tzdata-2015a-1.el7 or later is installed so that this leap second may be inserted for systems not synchronized by ntpd; this package was released from RHEA-2015:0141-1.

Using -x with ntp still results in instantaneous clock changes when leap second occurs; this issue is documented in Does Red Hat plan to release xleap.patch with ntp?.

In addition to the issues tracked above it is possible that application-specific issues will arise if the leap second was not considered during development. Issues of this nature are documented in Libraries and Applications do not account for the Leap Second.

Note: Red Hat recommends that customers using PPC and IA64 architectures use the method described under Systems not running NTP or PTP.

Realtime Kernels

A separate article has been created for tracking issues with realtime kernels. For more information refer to Resolve Leap Second Issues in Realtime (RT) kernels.