The Year 2038 problem is an issue for computing and data storage situations in which time values are stored or calculated as a signed 32-bit integer, and this number is interpreted as the number of seconds since 00:00:00 UTC on 1 January 1970 ("the epoch"). Such implementations cannot encode times after 03:14:07 UTC on 19 January 2038, a problem similar to but not entirely analogous to the "Y2K problem" (also known as the "Millennium Bug"), in which 2-digit values representing the number of years since 1900 could not encode the year 2000 or later. Most 32-bit Unix-like systems store and manipulate time in this "Unix time" format, so the year 2038 problem is sometimes referred to as the "Unix Millennium Bug" by association.
The latest time that can be represented in Unix's signed 32-bit integer time format is 03:14:07 UTC on Tuesday, 19 January 2038 (2,147,483,647 seconds after 1 January 1970). Times beyond that will "wrap around" and be stored internally as a negative number, which these systems will interpret as having occurred on 13 December 1901 rather than 19 January 2038. This is caused by integer overflow. The counter "runs out" of usable bits, "increments" the sign bit instead, and reports a maximally negative number (continuing to count up, toward zero). Resulting erroneous calculations on such systems are likely to cause problems for users and other relying parties.
Programs that work with future dates will begin to run into problems sooner; for example a program that works with dates 20 years in the future will have to be fixed no later than 2018.
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