Is Your PHP Application Affected by the Y2K38 Bug?

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I don’t want to be too alarmist, but try running the following PHP code on your system:

$date = '2040-02-01';
$format = 'l d F Y H:i';

$mydate1 = strtotime($date);
echo '<p>', date($format, $mydate1), '</p>';
With luck, you’ll see “Wednesday 1 February 2040 00:00” displayed in your browser. If you’re seeing a date in the late 60’s or early 70’s, your PHP application may be at risk from the Y2K38 bug!

What’s the Y2K38 bug?

Y2K38, or the Unix Millennium Bug, affects PHP and many other languages and systems which use a signed 32-bit integer to represent dates as the number of seconds since 00:00:00 UTC on 1 January 1970. The furthest date which can be stored is 03:14:07 UTC on 19 January 2038. Beyond that, the left-most bit is set and the integer becomes a negative decimal number — or a time prior to the epoch. Yes, it’s 28 years away and I’m sure many of you think it’s ridiculous to worry about it now. However, developers thought that way about the Millennium bug the 1970’s and 80’s. Also, any web application which handles long-term future events could be at risk. For example, a typical mortgage runs for 25 years. Pensions and savings plans can be far longer.

Will 64-bit save us?

Probably. If you’re using a 64-bit OS with a compiled 64-bit edition of PHP, your application shouldn’t be affected. I’d recommend you test it, though. A signed 64-bit number gives a maximum future date which is 21 times greater than the current age of the universe — 292 billion years, give or take a day or two. You can probably sleep at night if you’re convinced your financial application will always be installed on a 64-bit system.

Are there alternative options?

Fortunately, PHP introduced a new DateTime class in version 5.2 (experimental support was available in 5.1 and be aware that some methods were introduced in 5.3)…

$date = '2040-02-01';
$format = 'l j F Y H:i';

$mydate2 = new DateTime($date);
echo '<p>', $mydate2->format($format), '</p>';
DateTime does not suffer from Y2K38 problems and will happily handle dates up to December 31, 9999. I might have paid off my mortgage by then! It may not be worth upgrading existing applications, but you should certainly consider the DateTime class when planning your next project. Has you experienced Y2K38 problems in your application? How did you fix it?

Frequently Asked Questions (FAQs) about the Y2K38 Bug in PHP Applications

What exactly is the Y2K38 bug in PHP applications?

The Y2K38 bug, also known as the Unix Millennium bug, is a software issue that arises due to the way Unix-based systems, including PHP, store date and time information. Unix systems represent time as a signed 32-bit integer which counts the number of seconds since January 1, 1970. This method will run out of usable integer values on January 19, 2038, causing systems to roll over to negative numbers and interpret the date as December 13, 1901. This can lead to significant errors and malfunctions in PHP applications that rely on date and time functions.

How can I check if my PHP application is affected by the Y2K38 bug?

To check if your PHP application is affected by the Y2K38 bug, you can create a simple test script that sets the system time to a date beyond January 19, 2038. If your application fails or behaves unexpectedly, it is likely affected by the bug. However, this method may not uncover all potential issues, so it’s recommended to thoroughly review your code for date and time functions that could be affected.

What are the potential impacts of the Y2K38 bug on my PHP application?

The Y2K38 bug can cause a variety of issues in PHP applications, depending on how they use date and time functions. These can range from minor inconveniences, such as incorrect timestamps, to major problems like data corruption or system crashes. Any functionality that relies on accurate date and time information, such as scheduling, reporting, or data analysis, could be affected.

How can I fix the Y2K38 bug in my PHP application?

Fixing the Y2K38 bug in a PHP application typically involves updating the system to use a 64-bit integer for time storage, which extends the usable date range well beyond 2038. This may require updating your PHP version, operating system, or hardware. Additionally, you should review your code for any date and time functions that could be affected and update them to handle dates beyond 2038 correctly.

Are there any tools or libraries available to help fix the Y2K38 bug?

Yes, there are several tools and libraries available that can help you fix the Y2K38 bug in your PHP application. For example, the PHP DateTime class provides methods for working with dates and times that are Y2K38 safe. Additionally, there are several third-party libraries available that provide extended date and time functionality.

What is the difference between 32-bit and 64-bit time storage?

The difference between 32-bit and 64-bit time storage lies in the range of values they can represent. A 32-bit integer can store values from -2,147,483,648 to 2,147,483,647, which limits the Unix timestamp to dates between December 13, 1901, and January 19, 2038. On the other hand, a 64-bit integer can store values from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807, extending the usable date range well beyond 2038.

Can the Y2K38 bug affect other parts of my system besides my PHP application?

Yes, the Y2K38 bug can potentially affect any part of your system that uses 32-bit Unix timestamps, including the operating system itself, databases, and other software. Therefore, it’s important to check all parts of your system for potential Y2K38 issues, not just your PHP application.

Are there any risks associated with fixing the Y2K38 bug?

Fixing the Y2K38 bug can potentially introduce new issues into your system, especially if it involves major changes like updating your PHP version or operating system. Therefore, it’s important to thoroughly test your system after making any changes to ensure that it still functions correctly.

How can I prevent future date and time bugs in my PHP application?

To prevent future date and time bugs in your PHP application, it’s recommended to always use 64-bit time storage and to use robust date and time functions that can handle a wide range of dates. Additionally, regular code reviews and testing can help catch potential issues before they become problems.

What other resources are available to help me understand and fix the Y2K38 bug?

There are many resources available online to help you understand and fix the Y2K38 bug, including documentation from, articles and tutorials on various programming websites, and discussions on programming forums like Stack Overflow. Additionally, you may find it helpful to consult with a knowledgeable colleague or hire a professional consultant.

Craig BucklerCraig Buckler
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Craig is a freelance UK web consultant who built his first page for IE2.0 in 1995. Since that time he's been advocating standards, accessibility, and best-practice HTML5 techniques. He's created enterprise specifications, websites and online applications for companies and organisations including the UK Parliament, the European Parliament, the Department of Energy & Climate Change, Microsoft, and more. He's written more than 1,000 articles for SitePoint and you can find him @craigbuckler.

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