Year 2038 problem (2038年问题)

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Animation showing how the date would reset, represented as a signed 32-bit integer (at 03:14:08 UTC on 19 January 2038).

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).[1] 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.

Technical cause[edit]

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 (231-1 = 2,147,483,647 seconds after 1 January 1970).[2] 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 digit bits, flips 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.

Early problems[edit]

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In May 2006, reports surfaced of an early manifestation of the Y2038 problem in the AOLserver software. The software was designed with a kludge to handle a database request that should "never" time out. Rather than specifically handling this special case, the initial design simply specified an arbitrary time-out date in the future. The default configuration for the server specified that the request should time out after one billion seconds. One billion seconds (approximately 32 years) after 01:27:28 UTC on 13 May 2006 (12 May 2006 in North America) is beyond the 2038 cutoff date. Thus, after this time, the time-out calculation overflowed and returned a date that was actually in the past, causing the software to crash. When the problem was discovered, AOLServer operators had to edit the configuration file and set the time-out to a lower value.[3][4]

Players of games or apps which are programmed to impose waiting periods[5] are running into this problem when they attempt to work around the waiting period on devices which harbor the coding, by manually setting their devices (such as the Nexus 7[6]) to a date past 19 January 2038, but are unable to do so, since a 32-bit Unix time format is being used.

Vulnerable systems[edit]

Embedded systems that use dates for either computation or diagnostic logging are most likely to be affected by the 2038 bug.

Many transportation systems from flight to automobiles use embedded systems extensively. In automotive systems, this may include anti-lock braking system (ABS), electronic stability control (ESC/ESP), traction control (TCS) and automatic four-wheel drive; aircraft may use inertial guidance systems and GPS receivers. However, this does not imply that all these systems will suffer from the bug. Many such systems will not require access to dates. For those that do, those systems which only track the difference between times/dates and not absolute times/dates will, by the nature of the calculation, not experience a problem. This is the case for automotive diagnostics based on legislative standards such as CARB (California Air Resources Board).[7]

Another major use of embedded systems is in communications devices, including cell phones and Internet appliances (routers, wireless access points, etc.) which rely on storing an accurate time and date and are increasingly based on UNIX-like operating systems. For example, the bug makes some Android devices crash and not restart when the time is changed to that date.[8]

Despite the modern 18–24 month generational update in computer systems technology, embedded systems are designed to last the lifetime of the machine in which they are a component. It is conceivable that some of these systems may still be in use in 2038. It may be impractical or, in some cases, impossible to upgrade the software running these systems, ultimately requiring replacement if 32-bit time_t limitations are to be corrected.

MySQL database's built-in functions like UNIX_TIMESTAMP() will return 0 after 03:14:07 UTC on 19 January 2038,[9] though a bug-fix was contributed on 22 March 2017.[10]

Data structures with time problems[edit]

Many data structures in use today have 32-bit time representations embedded into their structure. A full list of these data structures is virtually impossible to derive but there are well-known data structures that have the Unix time problem:

  • file systems (many file systems use only 32 bits to represent times in inodes)
  • binary file formats (that use 32-bit time fields)
  • databases (that have 32-bit time fields)
  • database query languages, like SQL that have UNIX_TIMESTAMP() like commands

Examples of systems utilizing data structures that may contain 32-bit time representations include:

  • embedded factory, refinery control and monitoring subsystems
  • assorted medical devices
  • assorted military devices

Any system making use of data structures containing 32-bit time representations will present risk. The degree of risk is dependent on the mode of failure.

NTP timestamps[edit]

The Network Time Protocol has a related overflow issue, which manifests itself in 2036, rather than 2038. The 64-bit timestamps used by NTP consist of a 32-bit part for seconds and a 32-bit part for fractional second, giving NTP a time scale that rolls over every 232seconds (136 years) and a theoretical resolution of 2−32 seconds (233 picoseconds). NTP uses an epoch of 1 January 1900. The first rollover occurs in 2036, prior to the UNIX year 2038 problem.

Implementations should disambiguate NTP time using a knowledge of the approximate time from other sources. Since NTP only works with the differences between timestamps and never their absolute values, the wraparound is invisible in the calculations as long as the timestamps are within 68 years of each other. However, after a wraparound the clients can still face 2 problems: 1) They receive the date 01-01-1900 00:00:00UTC, not 07 feb 2036 06:28:15 (plus minus some leap seconds) as the new time; and 2) when a client tries to adopt this time and store it in UNIX time format, as many embedded systems do, it will fail because UNIX time starts at 13 December 1901 (signed 32 bit integer) or 01 January 1970 (unsigned 32 bit integer).

This means that for NTP the rollover will be invisible for most running systems, since they will have the correct time to within a very small tolerance. However, systems that are starting up need to know the date within no more than 68 years. Given the large allowed error, it is not expected that this is too onerous a requirement. One suggested method is to set the clock to no earlier than the system build date or the release date of the current version of the NTP software. Many systems use a battery-powered hardware clock to avoid this problem.

Even so, future versions of NTP may extend the time representation to 128 bits: 64 bits for the second and 64 bits for the fractional-second. The current NTP4 format has support for Era Number and Era Offset, that when used properly should aid fixing date rollover issues. According to Mills, "The 64 bit value for the fraction is enough to resolve the amount of time it takes a photon to pass an electron at the speed of light. The 64 bit second value is enough to provide unambiguous time representation until the universe goes dim."[11][note 1]

Solutions[edit]

There is no universal solution for the Year 2038 problem. Any change to the definition of the time_t data type would result in code compatibility problems in any application in which date and time representations are dependent on the nature of the signed 32-bit time_tinteger. For example, changing time_t to an unsigned 32-bit integer, which would extend the range to the year 2106, would adversely affect programs that store, retrieve, or manipulate dates prior to 1970, as such dates are represented by negative numbers. Increasing the size of the time_t type to 64-bit in an existing system would cause incompatible changes to the layout of structures and the binary interface of functions.

There is also no universal solution for the issue with DVB and ATSC real time transmitted dates due to issues with legacy receivers. The issue has yet to be acknowledged or resolved by either organization. The only workaround would be to discontinue all time-related metadata services such as programming guides and automatic date synchronization after the affected dates. One possible option would be to create new table types for the affected part of the specifications and use ISO 8601 date strings rather than fixed integers—as are used in ISO 9660 and ISO 13346 filesystems.

Most operating systems designed to run on 64-bit hardware already use signed 64-bit time_t integers. Using a signed 64-bit value introduces a new wraparound date that is over twenty times greater than the estimated age of the universe: approximately 292 billion years from now, at 15:30:08 UTC on Sunday, 4 December 292,277,026,596. The ability to make computations on dates is limited by the fact that tm_year uses a signed 32 bit integer value starting at 1900 for the year. This limits the year to a maximum of 2,147,485,547 (2,147,483,647 + 1900).[12]

Starting with NetBSD version 6.0 (released in October 2012), the NetBSD operating system uses a 64-bit time_t for both 32-bit and 64-bit architectures. Applications that were compiled for an older NetBSD release with 32-bit time_t are supported via a binary compatibility layer, but such older applications will still suffer from the Year 2038 problem.[13]

OpenBSD since version 5.5, released in May 2014, also uses a 64-bit time_t for both 32-bit and 64-bit architectures. In contrast to NetBSD, there is no binary compatibility layer. Therefore, applications expecting a 32-bit time_t and applications using anything different from time_t to store time values may break.[14]

Linux uses a 64-bit time_t for 64-bit architectures only; the pure 32-bit ABI is not changed due to backward compatibility.[15] There is ongoing work, mostly for embedded Linux systems, to support 64-bit time_t on 32-bit architectures, too.[16][17]

The x32 ABI for Linux (which defines an environment for programs with 32-bit addresses but running the processor in 64-bit mode) uses a 64-bit time_t. Since it was a new environment, there was no need for special compatibility precautions.[15]

Network File System version 4 has defined its time fields as struct nfstime4 {int64_t seconds; uint32_t nseconds;} since December, 2000.[18] Values greater than zero for the seconds field denote dates after the 0-hour, January 1, 1970. Values less than zero for the seconds field denote dates before the 0-hour, January 1, 1970. In both cases, the nseconds (nanoseconds) field is to be added to the seconds field for the final time representation.

Alternative proposals have been made (some of which are in use), such as storing either milliseconds or microseconds since an epoch (typically either 1 January 1970 or 1 January 2000) in a signed 64-bit integer, providing a minimum range of 300,000 years at microsecond resolution.[19][20] Other proposals for new time representations provide different precisions, ranges, and sizes (almost always wider than 32 bits), as well as solving other related problems, such as the handling of leap seconds. In particular, TAI64[21] is an implementation of the Temps Atomique International standard, the current international real-time standard for defining a second and frame of reference.

See also[edit]

Notes[edit]

  1. Jump up^ 2−64 seconds is about 54 zeptoseconds or 54 x 10−21 seconds (light would travel 16.26 picometres, or approximately 0.31 × Bohr radius), and 264 seconds is about 585 billion years.

References[edit]

  1. Jump up^ "The Open Group Base Specifications Issue 6 IEEE Std 1003.1, 2004 Edition (definition of epoch)". IEEE and The Open Group. The Open Group. 2004. Retrieved 7 March 2008.
  2. Jump up^ Diomidis Spinellis (2006). Code quality: the open source perspective. Effective software development series in Safari Books Online (illustrated ed.). Adobe Press. p. 49. ISBN 0-321-16607-8.
  3. Jump up^ "The Future Lies Ahead". 28 June 2006. Retrieved 19 November 2006.
  4. Jump up^ Weird "memory leak" problem in AOLserver 3.4.2/3.x 12 May 2006
  5. Jump up^ "It isn't cheating it's time travel".
  6. Jump up^ "25 Years From Today A Time For Bugs". Archived from the original on 21 January 2013. Update: I have confirmed Mikko's Android report on a Google Nexus 7 tablet running Android 4.1 Jelly Bean — Even though years beyond 2038 are listed in the Set Date and Time function of the Settings app, try to set it to a date past 1/19/2038 and it refuses.
  7. Jump up^ board, california air resources. "ARB Test Methods / Procedures". www.arb.ca.gov.
  8. Jump up^ "Sign in - Google Accounts". code.google.com.
  9. Jump up^ "aj_blk: Year 2038 Bug". Ajoeblk.blogspot.in. Retrieved 2013-03-12.
  10. Jump up^ "MySQL Bugs: #12654: 64-bit unix timestamp is not supported in MySQL functions". bugs.mysql.com.
  11. Jump up^ University of Delaware Digital Systems Seminar presentation by David Mills, 2006-04-26
  12. Jump up^ "The End of Time". 17 April 2010. Retrieved 19 March 2012.
  13. Jump up^ "Announcing NetBSD 6.0". 17 October 2012. Retrieved 18 January 2016.
  14. Jump up^ "OpenBSD 5.5 released (May 1, 2014)". 1 May 2014. Retrieved 18 January 2016.
  15. ^ Jump up to:a b Jonathan Corbet (14 August 2013). "Pondering 2038". Archived from the original on 4 March 2016. Retrieved 9 March2016.
  16. Jump up^ Arnd Bergmann (25 March 2015). "The end of time (32bit edition)" (PDF). Archived from the original (PDF) on 22 September 2015. Retrieved 9 March 2016.
  17. Jump up^ Jonathan Corbet (5 May 2015). "System call conversion for year 2038". Archived from the original on 11 October 2015. Retrieved 9 March 2016.
  18. Jump up^ "RFC 7530".
  19. Jump up^ "Unununium Time". Archived from the original on 8 April 2006. Retrieved 19 November 2006.
  20. Jump up^ Sun Microsystems. "Java API documentation for System.currentTimeMillis()". Retrieved 29 Sep 2017.
  21. Jump up^ "TAI64".

External links[edit]

========================

2038年问题

 编辑
2038年问题是指在使用POSIX时间的32位计算机应用程序上，格林尼治时间2038年1月19日凌晨03:14:07（北京时间：2038年1月19日中午11:14:07）之后无法正常工作。
网络时代，机会与危机共存，这也许是你我必须面对和必须付出的代价。“千年虫”解决之后，会不会有新的“虫”出现？回答是肯定的，“2038年”就是一个新的关卡。
 
中文名
2038年问题
外文名
Year 2038 problem
概    念
计算机bug（程序错误）
载    体
使用POSIX时间的32位应用程序
爆发时间
2038年1月19日03:14:07（UTC）

目录

  1. 1 32位时间表示
  2. ▪ 前言
  3. ▪ 正文
  4. 2 64位时间表示
  5. 3 解决进展

32位时间表示

编辑

前言

2038年问题演示2038年问题演示
在计算机应用上，2038年问题可能会导致某些软件在2038年无法正常工作。所有使用POSIX时间表示时间的程序都将受其影响，因为它们的时间起点是格林尼治时间1970年1月1日0时0分0秒（这个时间名叫 the Unix Epoch），它们用the Unix Epoch经过的秒数（忽略闰秒）来表示时间。这种时间表示法在类Unix（Unix-like）操作系统上是一个标准，并会影响以其C编程语言开发给其他大部份操作系统使用的软件。在大部分的32位操作系统上，此“time_t”数据模式使用一个有符号32位整数(signed int32)存储计算的秒数。依照此“time_t”标准，在此格式能被表示的最后时间是第2147483647秒（代表格林尼治时间2038年1月19日凌晨03:14:07）。下一秒，即格林尼治时间2038年1月19日凌晨03:14:08，由于32位整型溢出，时间将会被“绕回”（wrap around）成一个负数，变成了第 -2147483648 秒（代表格林尼治时间1901年12月13日20:45:52），造成应用程序发生严重的时间错误，而无法运行。

正文

也许大家都已经知道计算机的2000年问题是什么概念，但是什么时候又冒出来一个2038年问题的呢？
用C语言编制的程序不会碰到2000年问题，但是会有2038年问题。这是因为，大多数C语言程序都使用到一个叫做“标准时间库”的程序库，这个时间库用一个标准的4字节也就是32位的形式来储存时间信息。
当初设计的时候，这个4字节的时间格式把1970年1月1日凌晨0时0分0秒（这个时间名叫 the Unix Epoch）作为时间起点，这时的时间值为0。以后所有的时间都是从这个时间开始一秒一秒累积得来的。
比方说如果时间已经累积到了919642718这个数值，就是说这时距离 the Unix Epoch已经过去了919642718秒，换算一下就应该是1999年2月21日16时18分38秒。
这样计算时间的好处在于，把任意两个时间值相减之后，就可以很迅速地得到这两个时间之间相差的秒数，然后你可以利用别的程序把它换算成明白易懂的年月日时分秒的形式。
要是你曾经读过一点儿关于计算机方面的书，你就会知道一个4字节也就是32位的存储空间的最大值是2147483647，请注意！2038年问题的关键也就在这里———当时间一秒一秒地跳完2147483647那惊心动魄的最后一秒后，你猜怎么样？
答案是，它就会转为负数也就是说时间无效。那一刻的准确的时间为2038年1月19日星期二凌晨03:14:07，之后所有用到这种“标准时间库”的C语言程序都会碰到时间计算上的麻烦。
这就是2038年问题。
但是大家也不用太过紧张。2038年问题比千年虫（the Millennium bug）问题解决起来相对要容易一些，只要给那些程序换一个新版本的“标准时间库”就可以了，比如说，改用8字节64位的形式来存储时间。这样做并不怎么费事，因为在C程序中“标准时间库”是相对独立的一个部分，里面的时间表达都有自己的一套时间类型和参数（而在碰到Y2K的那些大型主机中，时间格式大都没有一）。
说到这里，一些冰雪聪明的菜鸟DDMM们应该可以联想到，WindowsNT用的是64位操作平台，它的开始时间是1601年1月1日———但是它每过1个纳秒就跳一下，因此，WindowsNT它会碰到的是2184年问题……
而在一些用64位来表示时间的平台上，例如DigitalAlpha、SGI、Sparc等等，想要看到它们的时间出错你得等到天荒地老———那大概是2920亿年。到那时，位于猎户座旋臂的太阳，已经是黑矮星或暗黑物质，猎户座旋臂已经被重力波震断，银河系大概则已经变成小型似星体了。
所以，给那些准备攒机的菜鸟DD一个建议，除非您想要把资料流传给下一个宇宙，一台64位的电脑已经足够。
总之，32位的最后时间是2038年1月19日03:14:07，星期二。
64位的最后时间约2900亿年后的292,277,026,596年12月4日15:30:08，星期日。

64位时间表示

编辑
新的64位运算器可以记录至约2900亿年后的292,277,026,596年12月4日15:30:08，星期日（UTC）。

解决进展

编辑
目前并没有针对现有的CPU/操作系统搭配的简单解决方案。直接将POSIX时间更改为64位模式将会破坏对于软件、数据存储以及所有与二进制表示时间相关的部份的二进位兼容性。更改成无符号的32位运算器（integer）则会影响许多与时间改变相关的程序。
大部份64位操作系统已经把time_t改为64位整型。不过，其他现有架构的改动仍在进行中，不过预期“应该可以在2038年前完成”。然而，直到2006年，仍然有数以亿计的32位操作系统在运行中，特别是许多嵌入式系统。相对于一般电脑科技18至24个月的革命性更新，嵌入式系统可能直至使用寿命终结都不会改变。32位time_t的使用亦被编码于文件格式，例如众所周知的ZIP压缩格式。其能存在的时间远比受影响的机器长
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原文地址：https://www.cnblogs.com/kungfupanda/p/8355981.html