Comprehensive Guide to PHP Error Logging and Debugging Techniques

PHP remains a dominant force in the backend development realm, powering over 77% of websites worldwide. Major platforms like WordPress, Facebook (legacy), and Wikipedia owe their functionality to PHP, proving its enduring relevance (source: W3Techs). While modern alternatives like Node.js and Python continue to rise, PHP’s simplicity, flexibility, and extensive support ecosystem keep it firmly at the core of web development. For developers seeking a reliable, scalable solution, PHP’s time-tested strengths make it a top choice for building dynamic and robust websites.

Benefits of Effective Error Logging

1. ✅ Early Detection of Bugs and Anomalies

Error logs serve as the first line of defense in identifying software bugs. By capturing unexpected behavior or failed operations as they occur, developers can pinpoint issues long before users report them. This proactive approach dramatically reduces the time spent hunting down obscure bugs.

2. 🔧 Smooth and Efficient Debugging During Development

During the development phase, having detailed error messages and backtraces allows engineers to troubleshoot and iterate faster. PHP error logs provide critical context, such as file paths, line numbers, and stack traces, enabling developers to zero in on faulty logic without guesswork.

3. 🤫 Silent Error Handling in Production

In production environments, errors should never be exposed directly to users. Logging errors silently in the background ensures that issues are captured discreetly without interrupting user experience or revealing internal code structures. This separation of user-facing behavior from backend diagnostics is key to maintaining professionalism and trust.

4. 🔐 Improved Application Security

Exposed error messages can unintentionally leak sensitive information, such as server paths, database credentials, or internal API structures. Proper error logging—combined with disabling on-screen error display in production—helps mitigate security risks by ensuring that errors are captured safely and reviewed only by authorized personnel.

Types of PHP Errors

PHP errors arise when there is something erroneous inside the code. They can be as complicated as calling an invalid variable or as easy as skipping a semicolon. Understanding the types of errors is essential before solving them effectively. 

• Warning Error

The warnings in PHP flag potential issues before they escalate into critical problems. Errors of type “warning” are generated when an invalid file path is used, but they do not halt program execution.

If this issue occurs, for instance, you may need to double-check the file’s name in the code or directory; the script may not have been able to locate it because of the syntax problem.

• Notice Error

Like warning errors, notice errors do not stop code execution and are therefore considered lower severity. These mistakes can make it difficult for the system to determine whether or not an error occurred or whether it is simply the expected result of a certain piece of code. The script requires access to an undefined variable, which causes a notice error.

• Syntax Error

Most syntax errors result from misplaced, mistyped, or misinterpreted symbols. The script is terminated when the error is detected by the compiler.

Syntax and parsing problems arise when semicolons and parentheses are missing or used incorrectly, due to misspellings, or due to open brackets or quotes.

• Fatal Error

A fatal error occurs if the function is called in the code yet the function is undefined. A fatal error in PHP stops the program from running and may even cause it to crash. Fatal errors fall into three categories:

• When the framework is unable to run the code because of an error in the installation process, a fatal error is reported during startup.
• When a developer makes use of a variable or data type that does not exist, a fatal error is generated at compile time.
• A fatal error that occurs during program execution is called a runtime fatal error and is identical to the compile time fatal error.

PHP Error Logging

Most websites and web apps today are written in PHP. According to w3techs, PHP powers 77.55% of websites across the globe as a server-side programming language. These numbers pinpoint that PHP continues to have a sizable part of the programming language industry. 

When you first begin developing a PHP program, you use commands like print r() and var dump() to debug the errors and log in to the site. Working in production mode, however, requires a more secure method. You can do that in the development mode, but you must disable it while migrating. 

Thus, when in development mode, logging errors in PHP is as simple as calling the error log() function, which will then forward the error message to the program’s predefined error handling procedures.  If, for example, PHP is unable to establish a connection to a MySQL database, you can log key errors in the following manner:

<?php

// Send error message to the server log if error connecting to the database

if (!mysqli_connect("localhost","bad_user","bad_password","my_db")) {

   error_log("Failed to connect to database!", 0);

}

// Send email to administrator if we run out of FOO

if (!($foo = allocate_new_foo())) {

   error_log("Oh no! We are out of FOOs!", 1, "[email protected]");

}

?>

Enabling Error Logging in php.ini

PHP errors can be logged by opening the php.ini file and adding or uncommenting the lines of code below:

error_reporting = E_ALL & ~E_NOTICE

error_reporting = E_ALL & ~E_NOTICE | E_STRICT

error_reporting = E_COMPILE_ERROR|E_RECOVERABLE_ERROR|E_ER… _ERROR

error_reporting = E_ALL & ~E_NOTICE

Enabling PHP error logs in an individual file is simple. Just add the following lines of code at the beginning of the PHP file.

ini_set('display_errors', 1);

ini_set('display_startup_errors', 1);

error_reporting(E_ALL);

For parsing the log errors in the php.ini file, enable the following:

display_errors = on

The logged errors are displayed in the browser. You can also use the following commands to log PHP errors:

// Turn off all error reporting

error_reporting(0);

// Report simple running errors

error_reporting(E_ERROR | E_WARNING | E_PARSE);

// Reporting E_NOTICE can be good too (to report uninitialized variables or catch variable name misspellings ...)

error_reporting(E_ERROR | E_WARNING | E_PARSE | E_NOTICE);

// Report all errors except E_NOTICE

error_reporting(E_ALL & ~E_NOTICE);

// Report all PHP errors (see changelog)

error_reporting(E_ALL);

// Report all PHP errors

error_reporting(-1);

// Same as error_reporting(E_ALL);

ini_set('error_reporting', E_ALL);

Viewing PHP Logging Error

PHP error logging is turned off by default and can only be accessed when an error occurs. Before making any modifications to the code or configuration, you should first verify that logging is enabled in the PHP settings for your PHP hosting account.

1. Use the .htaccess File

Changing the .htaccess file enables the PHP error log. Using a file manager or FTP client, search for the .htaccess file in the website’s root directory. In case the file is hidden, you will need to change the settings in the control panel or your FTP client.

When the .htaccess file has been located, proceed as follows. In the .htaccess file, add this code:

php_flag log_errors on

php_value error_reporting 32767

php_value error_log “error_log.txt

• Under the public_html directory, create a file named error_log.txt.
• Close the file after saving.
• The error_log.txt file will contain all the PHP errors.

Local Value must now be active as error logging has been facilitated for PHP. Even when the Master Value is off, it would be overridden by the local value.

You can view the PHP error logs by opening the error_log.txt file if the website has any problems.

2. Use the php.ini File

One way to activate the PHP error log is by editing the php.ini file. It comes preconfigured web server that helps to run the PHP applications.  The php.ini configuration file can be accessed through the PHP information. Use CTRL + F (Windows) or Command + F (Mac OS) to open up the search box. Look for “Loaded Configuration File.”

You can also make use of the command line to locate the configuration file. Use an SSH client for connecting to the web server. Run the following command:

php -i | grep php.ini

Following is the output:

Here are some directories for php.ini for various operating systems:

1. For CLI: /etc/php/7.4/cli/php.ini. Modifications in the PHP configurations in CLI do not have any effect on the web server. 
2. For Nginx or Apache with PHP-FPM: /etc/php/7.4/fpm/php.ini
3. For Apache: /etc/php/7.4/apache2/php.ini.

Copying PHP Error Logs to File

When working in a development setting, the above-described procedures are useful. But, once your site is live and you’re in production mode, you’ll need to hide the problems from the user interface and instead log them in a separate file. They should be kept in the PHP.ini-defined error logs location.

If PHP is configured to use an Apache2 module, the error logs will be kept in the /var/log/apache2 directory. PHP error log files are usually stored in your root directory’s /log subfolder on shared hosting. Nevertheless, if you have access to the php.ini file, you can change this:

error_log = /var/log/php-scripts.log

The master log file in cPanel is located at:

/usr/local/apache/logs/error_log

When nothing works, you can use the following:

<?php phpinfo(); ?>

Error logging in PHP Frameworks

You can use the above methods for core PHP development. However, many micro-frameworks and Model View Architecture (MVC) have been built on top of PHP’s fundamental functionality, each adding its own set of practices. CodeIgniter, Symfony, and Laravel are a few of the top PHP MVC frameworks for developing complex online applications. 

In new Laravel projects, exception handling and error logging are already set up. Laravel’s App\Exceptions\Handler class is dedicated to handling such situations. Laravel uses the powerful Monolog library to log errors. It preconfigures several such handlers, offering the choice of using a PHP error log file, writing error information to the system log, and rotating log files. 

Configuring the PHP option to display error messages to the user can be done in the config/app.php file. APP_DEBUG is an environment variable whose value can be adjusted in the.env file and then reflected in the app.php configuration. This value can be true during local development but must be false once migrated to production. An error message displayed in the browser indicates a potential security risk.

As a developer, you have the option of storing Laravel log information in a variety of formats, including an error log, Syslog,  and the daily file. The app.php file is where you’ll make changes to the log option to configure Laravel error logging. For example, here’s how you’d go about establishing daily error logging:

‘log’ => ‘daily’

Errors accompanied by various security alerts can be documented in Monolog. It retains all errors by default, but you can classify them as emergency, error, critical, warning, or alert. To accomplish this effect, simply include the following attribute in your options:

‘log_level’ => env(‘APP_LOG_LEVEL’, ‘error’),

The log file can be found in storage/logs. Log facades can also be used to record errors.

<?php

namespace App\Http\Controllers;

use App\User;

use Illuminate\Support\Facades\Log;

use App\Http\Controllers\Controller;

class UserController extends Controller

{

   /**

    * Show the profile for the given user.

    *

    * @param  int $id

    * @return Response

    */

   public function showProfile($id)

   {

       Log::info('Showing user profile for user: '.$id);

       return view('user.profile', ['user' => User::findOrFail($id)]);

   }

}

The logger provides eight different logging levels, including:

Log::emergency($message);

Log::alert($message);

Log::critical($message);

Log::error($message);

Log::warning($message);

Log::notice($message);

Log::info($message);

Log::debug($message);

Error Logging In Symfony

You can insert the default Symfony logger, which displays various warning levels, inside the controller. Log entries in the var/log/prod.log file are written to the var/log/dev.log file by default.

use Psr\Log\LoggerInterface;

public function index(LoggerInterface $logger)

{

   $logger->info('I just got the logger');

   $logger->error('An error occurred);

   $logger->critical('I left the oven on!', [

       // include extra "context" info in your logs

       'cause' => 'in_hurry',

   ]);

   // ...

}

The Laravel framework shares the same warning levels as its progenitor, Symfony.

For error logging, Symfony relies on Monolog and provides a default monolog.yaml with several pre-configured handlers. The following is an example of a log file that was written using syslogs:

// config/packages/prod/monolog.php

$container->loadFromExtension('monolog', [

   'handlers' => [

       'file_log' => [

           'type' => 'stream',

           'path' => '%kernel.logs_dir%/%kernel.environment%.log',

           'level' => 'debug',

       ],

       'syslog_handler' => [

           'type' => 'syslog',

           'level' => 'error',

       ],

   ],

]);

How to Automate the PHP Error Logging Process

While it is possible to manually report all failures, doing so can become tedious and time-consuming when working on many teams or large-scale projects. This is why it is important to implement a workflow that automatically records problems in third-party tools like Sentry, Blackfire, Slack,  etc.

With these resources, you can learn more about problem causes and potential fixes. Slack channels can be set up to instantly alert everyone working on a project if something goes wrong during execution. Symfony is a good reference for a framework that follows a similar pattern.

Best Practices for Error Logging in PHP: A Detailed Guide

1. Log Errors in Separate Files

In a large PHP application, different parts of your application will generate different types of errors. It’s crucial to log these errors in separate files based on their source or severity. This practice simplifies debugging by isolating issues to specific modules, making it much easier to identify the root cause of problems.

For example:

• Database Errors: A dedicated log file for database-related errors can capture failed queries, connection issues, or slow database responses.
• Authentication Errors: A separate log for authentication errors helps you monitor failed login attempts or unauthorized access attempts.
• Form Submission Issues: Log form validation errors or issues with file uploads in their own file for quick access and troubleshooting.

By separating logs by type or module, you can streamline your workflow and pinpoint the exact part of your application that is causing the issue.

Benefits:

• Easier to identify and debug specific issues.
• Reduces clutter in error logs, making them more readable.
• Improves collaboration between team members by providing clear error categories.

2. Use Rotating Logs

Over time, error logs can grow in size and take up valuable disk space, especially in high-traffic applications. Log rotation is the practice of archiving older logs and starting new log files periodically. By using log rotation, you can prevent your log files from growing indefinitely and consuming excessive storage.

What is Log Rotation?
Log rotation involves setting up automatic processes that archive or compress old logs and create new log files at regular intervals. This ensures that your server doesn’t run out of space while maintaining historical data in a manageable format.

Tools for Log Rotation:

• Logrotate: A widely used Linux tool that automates the rotation of log files, making it easier to manage log data.
• Custom Rotation Scripts: If you have specific needs, you can write your own rotation scripts to handle log files based on certain conditions, such as file size or age.

Benefits:

• Helps prevent disk space issues by managing large log files.
• Allows for easy archival and retrieval of older logs when needed.
• Automates the process of maintaining logs, saving time and reducing the chance of manual errors.

3. Avoid Displaying Errors on Live Sites

While displaying error messages during development can be incredibly helpful, you must never display errors on live websites or production servers. Exposing detailed errors, such as database paths or server information, to users is a significant security risk.

For example, an error like Warning: include() failed to open stream might reveal the path to your server’s file system, giving attackers valuable information about the structure of your application. Instead, you should configure PHP to log errors to a secure file and display generic error messages to users.

Best Practices for Displaying Errors:

• Disable error display: In production environments, set the display_errors directive to Off in your php.ini file or override it in your script using ini_set.
• Use Custom Error Pages: Provide user-friendly error pages (e.g., 404 or 500) that don’t expose sensitive information while guiding users on how to proceed.

display_errors = Off

Benefits:

• Prevents leakage of sensitive information.
• Improves the security of your application by minimizing the risk of revealing server paths or database details.
• Enhances the user experience by displaying professional, customized error pages rather than technical error details.

4. Monitor Logs Regularly

Error logs should not be set up once and forgotten. It is crucial to monitor them regularly to catch issues early and ensure that your application is running smoothly. Regular monitoring helps you stay on top of any problems that arise, and allows you to take proactive steps before they affect end-users.

How to Monitor Logs Effectively:

• Automated Notifications: Set up automated notifications for critical errors (e.g., fatal errors, database failures) to alert your team when an issue arises.
• Third-Party Monitoring Tools: Integrate with tools like Loggly, Papertrail, or Sentry to get real-time alerts and error tracking. These platforms offer powerful search and filtering features to quickly pinpoint issues.
• Periodic Log Reviews: Schedule regular reviews of your logs, especially after significant code changes or system updates, to identify any new issues.

Benefits:

• Detects issues before they escalate and affect users.
• Saves time and resources by allowing teams to address errors promptly.
• Ensures high availability and reliability of your application.

5. Include Context in Your Logs

Logs are more useful when they contain contextual information. Including the right amount of detail in each log entry helps developers understand the circumstances surrounding an error. A simple log message with no context can be cryptic and challenging to debug, especially for larger applications.

Key Contextual Information to Include:

• Timestamp: Always include the exact date and time when the error occurred. This helps you correlate errors with specific events (e.g., server load spikes or code deployments).
• Error Type: Indicate whether the error is a warning, notice, or fatal error.
• User ID/Session: Include user-related data (without compromising privacy) to identify which users encountered the issue.
• File and Line Number: Include the file name and line number where the error occurred, helping developers trace the issue back to the source.
• Stack Trace: For critical errors, include a stack trace to show the sequence of function calls leading to the error.

error_log("ERROR: Failed to load user profile - User ID: 1234 | Time: " . date("Y-m-d H:i:s"));

Benefits:

• Makes it easier for developers to diagnose issues.
• Improves the quality and efficiency of debugging.
• Reduces the time it takes to resolve problems by providing all the necessary information in one place.

Common Error Logging Pitfalls to Avoid

1. Not Disabling Error Display in Production

One of the most critical mistakes developers make is leaving error display enabled in a production environment. While it’s essential to see detailed error messages during development to troubleshoot issues quickly, displaying such information on live websites can expose sensitive information to users, especially malicious actors.

When error display is enabled on a live site, it could reveal sensitive data such as file paths, database details, or internal server configurations. Attackers can use this information to exploit vulnerabilities in your application, potentially compromising the security of your website and its users.

Best Practice:
Always ensure that error messages are hidden in production environments. Instead of displaying raw error information, configure PHP to log errors to a secure file and show a user-friendly error page. This keeps the user experience intact while preserving sensitive data from exposure.

To disable error display in production:

• Modify your php.ini file to ensure display_errors is set to Off.
• Use ini_set to override settings in your PHP script if necessary.

Why It Matters:

• Security: Prevents attackers from gaining insight into the internal workings of your site.
• Professionalism: Enhances the user experience by showing helpful error pages instead of technical details.
• Confidentiality: Protects sensitive configuration and server data from being revealed to the public.

2. Overlooking Log Rotation

As your application grows and the number of errors increases, the log files can become very large over time. If you don’t rotate your logs regularly, they can quickly consume disk space, leading to performance degradation or, worse, filling up your server’s storage, which could result in your site going down. In addition, large log files become harder to manage, making it challenging to locate specific errors when troubleshooting.

Log rotation is the practice of archiving and compressing older log files and creating new ones. By doing this regularly, you can keep your logs manageable, improve server performance, and prevent potential storage issues.

Best Practice:

• Set up automatic log rotation using tools like logrotate (Linux) or custom scripts that manage log file size, retention, and archival.
• Rotate logs based on file size or time intervals (e.g., daily or weekly) to keep the system running smoothly.

Why It Matters:

• Performance: Prevents logs from growing too large and consuming excessive disk space.
• Efficiency: Makes it easier to manage and analyze log files, as older logs are archived and new logs are stored separately.
• System Stability: Ensures your server continues to function smoothly without being bogged down by large, unmanageable logs.

3. Ignoring Non-Critical Errors

Not all errors are catastrophic, but even non-critical ones, like notices or warnings, can indicate underlying issues in your application that need attention. These seemingly minor issues can often snowball into more significant problems if left unaddressed. For example, a small notice like “undefined variable” could indicate a deeper coding issue, such as a logic flaw or an incomplete feature that might cause more problems in the future.

Best Practice:

• Don’t ignore warnings and notices. Review and resolve them as part of your regular development process.
• Configure your error reporting to log all errors, including notices and warnings, but don’t display them to end-users in a production environment.
• Regularly review non-critical errors in your logs to identify trends and fix the root cause.

Why It Matters:

• Future Proofing: By addressing small issues early, you prevent larger, more complex problems from emerging later on.
• Proactive Debugging: Catch minor issues before they escalate into major bugs or performance problems.
• Code Quality: Ensures your code is clean, complete, and functioning optimally, even if the errors don’t break the app outright.

Learn about PHP exception handling here.

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Frequently Asked Questions (FAQ) about PHP Error Logging

What is PHP error logging?

PHP error logging refers to the process of capturing, storing, and reviewing errors that occur during the execution of PHP scripts. These logs provide insights into application failures, runtime issues, and misconfigurations.

Where are PHP error logs stored?

By default, PHP error logs are stored in a location defined in your php.ini file under the error_log directive. On most Linux systems, this is often /var/log/php_errors.log.