Among systems that reportedly experienced difficulty with the extra second were unpatched Linux OS kernels, Hadoop instances, Cassandra databases and Java-based programs. Enough problems were documented around the globe that some even leap second change to another Y2K.

were introduced in 1971, as way to synchronize official digital time keeping, called Coordinated Universal Time (UTC) and mean solar time, namely by adding or removing a second from the official time. Overseen by the International Telecommunications Union, UTC is defined by the accumulation of seconds, which are defined with great precision by atomic clocks. Solar time, in contrast, measures the day by the time it takes the Earth to do one complete rotation, which can fluctuate slightly due to tidal effects, the slowing of the earth's rotation and other factors.

On Saturday, the ITU onto the end of June 30 UTC, at midnight Greenwich Mean Time, or 8 p.m. Eastern daylight time, the 25th adjustment to UTC since 1971.

Typically, UTC is coordinated across the Internet using the Network Time Protocol (NTP), in which the official time, supplied by the U.S. Navy and other sources, is passed among Internet servers. The client software for NTP to accommodate the leap seconds when they occur. Additional solutions have been offered to better arm servers against possible leap second failures, including those introduced by and engineers.

For this leap second however, numerous problems were experienced. Those with servers running Debian Linux several servers going offline after the leap second occurred. The servers were restored after NTP was temporarily disabled.