Error Codes

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  1. Error Codes
    1. Introduction

Error codes are an unavoidable part of working with any software, and MediaWiki is no exception. They are diagnostic messages generated by the system when something goes wrong. Understanding these codes, even at a basic level, can be incredibly helpful in troubleshooting problems and getting your wiki running smoothly. This article aims to provide a comprehensive guide to error codes in MediaWiki, geared towards beginners. We will cover common types of errors, where to find more information about them, and basic steps you can take to resolve them. Ignoring error codes can lead to more significant problems down the line, so learning to interpret them is a valuable skill for any wiki administrator or editor. This article will not cover server-level errors (like PHP errors outside of MediaWiki's control) but will focus on errors *reported* by MediaWiki itself.

    1. What are Error Codes?

At their core, error codes are simply numeric or textual identifiers that represent specific problems. They are designed to be machine-readable (useful for logging and automated diagnostics) but are often presented to users in a human-readable format, although sometimes quite cryptic! MediaWiki utilizes a system of error codes to communicate issues related to database connections, file access, permissions, syntax within wiki pages, extension conflicts, and many other potential problems.

Think of them like a car's "check engine" light. The light itself doesn't *tell* you what's wrong, but it signals that *something* is wrong. Similarly, an error code tells you that a problem exists, and often gives a clue about its nature. You then need to investigate further to diagnose the root cause.

    1. Common Categories of MediaWiki Error Codes

MediaWiki error codes can be broadly categorized into several types:

  • **Database Errors:** These relate to issues connecting to or interacting with the database. Common causes include incorrect database credentials, database server downtime, corrupted database tables, or queries that violate database constraints. These are often accompanied by messages referencing MySQL, PostgreSQL, or SQLite.
  • **File Errors:** These errors occur when MediaWiki is unable to access or manipulate files. This could be due to incorrect file permissions, missing files, or insufficient disk space. These frequently occur when dealing with uploaded images or extension files.
  • **Syntax Errors:** These are the most common errors encountered by editors. They arise when there's a problem with the wiki markup used in a page. Examples include unbalanced brackets, incorrect template usage, or invalid parameters. The error message typically highlights the problematic section of code.
  • **Extension Errors:** Extensions are powerful tools for adding functionality to MediaWiki, but they can also introduce errors. These errors might be caused by conflicts between extensions, bugs within an extension, or incorrect configuration.
  • **Permission Errors:** These errors indicate that the user or the MediaWiki process lacks the necessary permissions to perform an action. This can relate to file access, database access, or access to system resources.
  • **Caching Errors:** MediaWiki uses caching extensively to improve performance. Errors related to caching can occur if the cache is corrupted or if there are issues with the caching system (e.g., Memcached).
  • **Internal Errors:** These are more general errors that don't fall neatly into any other category. They often indicate a bug within MediaWiki itself or a problem with the underlying PHP environment.
    1. Interpreting Error Messages

Error messages themselves can vary in clarity. Some are very specific, pointing directly to the source of the problem. Others are more vague, requiring more investigation. Here's a breakdown of how to approach interpreting them:

  • **Read the Entire Message:** Don't just focus on the error code itself. The surrounding text often provides valuable context and clues.
  • **Look for File Names and Line Numbers:** If the error message includes a file name and line number, it indicates the location in the code where the error occurred. This is particularly helpful for developers or those familiar with PHP.
  • **Identify Keywords:** Pay attention to keywords like "database," "file," "syntax," "extension," or "permission." These keywords can help you narrow down the potential cause of the error.
  • **Search the MediaWiki Documentation:** The official MediaWiki documentation is an invaluable resource for understanding error codes. Search for the error code or keywords from the error message to find relevant information.
  • **Search Online Forums and Communities:** The MediaWiki community is very active. Search online forums (like the MediaWiki forums) and Stack Exchange for discussions about the error code. Someone else may have already encountered and solved the same problem.
    1. Common Error Codes and Troubleshooting Steps

Here's a look at some common error codes and suggested troubleshooting steps. This is not an exhaustive list, but it covers many of the errors beginners are likely to encounter.

    • 1. "Database connection error"**
  • **Cause:** This indicates that MediaWiki cannot connect to the database server. Possible causes include incorrect database credentials (hostname, username, password), database server downtime, or network connectivity issues.
  • **Troubleshooting:**
   *   Verify your database credentials in `LocalSettings.php`.
   *   Ensure the database server is running.
   *   Check network connectivity between the web server and the database server.
   *   Test the database connection using a database client (e.g., phpMyAdmin).
    • 2. "Error: Could not open or write to the file..."**
  • **Cause:** MediaWiki is unable to access or modify a file. This could be due to incorrect file permissions, the file doesn't exist, or insufficient disk space.
  • **Troubleshooting:**
   *   Verify file permissions.  The web server user needs read and write access to the necessary files and directories.
   *   Ensure the file exists.
   *   Check disk space usage.
   *   Check for file locking issues (another process may be using the file).
    • 3. "Parse error: unexpected character in input"**
  • **Cause:** This is a common syntax error in wiki markup. It usually means there's an unmatched bracket, a misplaced character, or an invalid template parameter.
  • **Troubleshooting:**
   *   Carefully review the code in the affected page.
   *   Use the "Show preview" feature to identify the problematic section.
   *   Check for unbalanced brackets (``, ``, `Template:`, ``, `[`, `]`).
   *   Validate template usage and parameters.
    • 4. "Fatal error: Allowed memory size of X bytes exhausted"**
  • **Cause:** The PHP script ran out of memory. This can happen when processing large pages, complex templates, or when dealing with large images.
  • **Troubleshooting:**
   *   Increase the `memory_limit` setting in your `php.ini` file.
   *   Optimize the page or template to reduce memory usage.
   *   Consider using a caching mechanism to reduce the load on the server.
    • 5. "Extension 'X' is not installed"**
  • **Cause:** MediaWiki is trying to use an extension that is not installed or enabled.
  • **Troubleshooting:**
   *   Ensure the extension is installed in the `extensions` directory.
   *   Add the extension to the `$wgExtensions` array in `LocalSettings.php`.
   *   Clear the MediaWiki cache.
    • 6. "Warning: include(…): failed to open stream: No such file or directory"**
  • **Cause:** PHP cannot find a file that it's trying to include. This usually happens with extensions or custom configurations.
  • **Troubleshooting:**
   *   Verify the file path in the `include` statement.
   *   Ensure the file exists in the specified directory.
   *   Check file permissions.
    • 7. "Error: Invalid article title"**
  • **Cause:** The title of the page being created or edited contains invalid characters.
  • **Troubleshooting:**
   *   Ensure the title adheres to the MediaWiki title naming conventions. Avoid special characters, spaces, and reserved words.
    • 8. "Error: Too many open files"**
  • **Cause:** The server has reached its limit on the number of open files. This can happen under heavy load.
  • **Troubleshooting:**
   *   Increase the open file limit in your operating system configuration. (Requires server administrator access).
   *   Optimize your MediaWiki configuration to reduce the number of open files.
    1. Tools for Debugging

Several tools can help you debug MediaWiki errors:

  • **MediaWiki's Debug Mode:** Enable debug mode by setting `$wgDebug` to `true` in `LocalSettings.php`. This will display more detailed error messages. Be cautious about enabling this in a production environment, as it can expose sensitive information.
  • **PHP Error Logging:** Configure PHP to log errors to a file. This can provide valuable insights into the cause of the error.
  • **Web Browser Developer Tools:** Use your web browser's developer tools (usually accessible by pressing F12) to inspect network requests, JavaScript console output, and other debugging information.
  • **Database Query Logging:** Enable database query logging to track the SQL queries being executed by MediaWiki. This can help identify performance bottlenecks or problematic queries.
    1. Resources
    1. Further Learning

To deepen your understanding of MediaWiki and troubleshooting, consider exploring these topics:

Help:Contents

Manual:Configuration

Manual:Database

Manual:Extensions

Manual:Templates

Manual:Wiki Markup

Admin

Debugging

Maintenance

Security

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