PHP默认时区获取来源咨询：应用时间函数时区偏差问题排查

Hey there, let's unpack exactly how PHP picks its default timezone, and why your setup might have shifted from working correctly to showing times 4 hours ahead of EST.

First, PHP determines the default timezone in a specific priority order (from highest to lowest):

• Runtime function calls: Any explicit date_default_timezone_set() in your code will override all other settings. Since you said you didn't need this before, this isn't the culprit here.
• php.ini configuration: The date.timezone directive in your server's php.ini file is the primary default source for most setups. If this was previously set to America/New_York and got changed (maybe during a server update or config tweak), that would explain your current issue.
• System environment variable (TZ): If php.ini doesn't set a timezone, PHP will check the server's system-level TZ environment variable. For example, if your server's OS timezone was switched from EST to UTC, this would cause the time to jump 4 hours ahead.
• .htaccess (Apache-only): If you're using Apache web server, you can set the timezone directly in .htaccess with a line like php_value date.timezone "America/New_York". This overrides the php.ini setting, so if this line was removed or modified recently, that could be the cause.
• Compile-time default: If none of the above are set, PHP falls back to its compile-time default, which is almost always UTC. This matches your current situation—UTC is 4 hours ahead of EST, which explains the time mismatch you're seeing.

Why it worked before but now doesn't? #

The most likely scenarios are:

1. Your server's php.ini file was updated, and the date.timezone setting was reset to UTC or removed entirely.
2. A previously existing .htaccess timezone configuration was deleted or altered.
3. Your server's system timezone (the TZ variable) was changed during maintenance or an OS update.

How to verify? #

You can quickly check the current timezone settings by creating a simple PHP file with this code:

<?php
echo "Current PHP timezone: " . ini_get('date.timezone') . "<br>";
echo "System TZ variable: " . getenv('TZ') . "<br>";
phpinfo();
?>

Run this file in your browser, and look for the date.timezone entry under the "date" section, plus the TZ value in the "Environment" section. This will tell you exactly where PHP is getting its timezone from right now.

内容的提问来源于stack exchange，提问作者John Hubler