md5_file() debug log best practices

M66 2025-06-02

When using PHP to process files, md5_file() is a very practical function that can directly obtain the MD5 hash value of the file, which is used to verify file integrity or identify file uniqueness. However, in some cases, the function may return false instead of the expected 32-bit MD5 string. At this time, we need to troubleshoot through the debug log to find out the root cause.

1. Basic usage of md5_file() function

The basic syntax of md5_file() is as follows:

 $hash = md5_file('/path/to/file.txt');

If the file exists and is readable, the function returns the MD5 hash value (a 32-character hexadecimal string) of the contents of the file. Otherwise, it will return false .

2. Common reasons for returning false

To effectively troubleshoot problems, we must first clarify the common reasons that may cause md5_file() to return false :

File path error or does not exist
No read permission for the file
Files are occupied or locked by other processes
PHP environment is restricted, such as open_basedir restriction
File system exception or hardware error

3. Turn on the logging check steps

To facilitate tracking of problems, you can add logging to the error, or enable error logs by configuring the php.ini file.

1. Enable PHP error log

In php.ini , enable error logs and set the log file path:

 log_errors = On
error_log = /var/log/php_errors.log

After restarting the PHP or Web server, all runtime errors of PHP are written to the log file.

2. Use custom logging

In addition to system logs, developers can also add custom logs for details tracking. For example:

 $file = '/path/to/file.txt';

if (!file_exists($file)) {
    error_log("The file does not exist: " . $file);
} elseif (!is_readable($file)) {
    error_log("File not readable: " . $file);
} else {
    $md5 = md5_file($file);
    if ($md5 === false) {
        error_log("md5_file() return false: " . $file);
    } else {
        error_log("document MD5: " . $md5);
    }
}

In this way, the status of each step can be recorded, which helps quickly locate the problem.

4. Online debugging suggestions

In production environments, it is recommended to write debug information to a custom log file instead of a system error log to avoid affecting other modules:

 function debug_log($message) {
    $logFile = '/var/log/md5_debug.log';
    error_log(date('[Y-m-d H:i:s] ') . $message . "\n", 3, $logFile);
}

Usage example:

 debug_log("开始计算document MD5：" . $file);

5. Use tools to verify file status

External PHP, you can also use the command line tool to verify file status. For example:

 ls -l /path/to/file.txt
md5sum /path/to/file.txt

In addition, you can also write scripts to automatically verify whether multiple files can calculate MD5 values normally.

VI. Typical case analysis

Suppose you have problems in the following code:

 $url = 'https://m66.net/files/sample.zip';
$path = '/var/www/files/sample.zip';

$md5 = md5_file($path);
if ($md5 === false) {
    error_log("无法获取document {$path} of MD5 value");
}

We need to confirm:

Whether the sample.zip file actually exists in the specified directory.
Whether the PHP process has permission to access the path.
Is there any other program that occupies the file.

By gradually checking and adding debug logs, you can quickly narrow the scope of troubleshooting and ultimately locate problems.

Conclusion

Although the problem of md5_file() returning false is common, it can be easily solved as long as you master the appropriate debugging methods and logging skills. Whether in development or production environments, logging is a powerful tool for discovering and solving problems. Mastering it and making good use of it can greatly improve the efficiency of investigation and code robustness.

md5_file