Drupal 911 - What To Do When Your Drupal Site is Broken

Help! My Drupal site is down!!! While Drupal has proven itself as a highly reliable platform for enterprise-class web sites, there are instances when problems occur and Drupal websites go down. All one has to do is to browse the various Drupal discussion forums around the web and you're likely to see several late night pleas for help on how to fix a particular problem. If you are a person in that situation - posting on a forum and crossing your fingers that someone is watching the thread and responds in a timely manner may not be the most effective means of solving a Drupal production problem.
 

Aha Consulting is in the process of creating a Drupal 911 handbook that provides a searchable repository of common Drupal production issues. Each issue will include a description of the likely symptoms that you may be experiencing as well as the likely causes and approaches for remediating those problems. Intended as a Drupal community resource, Aha's Drupal 911 handbook will be available and searchable by anyone with web access. Our goal is to provide a tool that allows Drupal administrators with easy to search content that provides quick answers to common Drupal production problems.
 

An example of content that we are working on includes:
 

Symptom:
My Drupal site displays the unable to connect to the database error page


Likely Causes:
1) MySQL is down,
2) Someone changed the MySQL user name and/or password,
3) Someone changed the settings.php file


How to Fix it
1) if you have access to the server, check to ensure that MySQL is up and running and is accessible. There are several ways to do this including PHPmyAdmin or command line MySQL.
2) Verify that the user-id and password for the MySQL account used by Drupal still exists and has not changed
3) Verify that the database parameters in your settings.php file matches the configuration that is set up in MySQL (check the URL for the database set in /sites/all/default/settings.php)