Fix WordPress "Error Establishing Database Connection"

Understanding the Error

WordPress cannot connect to MySQL/MariaDB database.

Step 1: Check MySQL is Running

sudo systemctl status mysql
sudo systemctl status mariadb

# Start if stopped
sudo systemctl start mysql

Step 2: Verify Database Credentials

Check wp-config.php:

define( 'DB_NAME', 'database_name' );
define( 'DB_USER', 'database_user' );
define( 'DB_PASSWORD', 'password' );
define( 'DB_HOST', 'localhost' );  // Usually localhost

Test credentials manually:

mysql -u database_user -p -h localhost database_name

Step 3: Check MySQL User Privileges

# As root MySQL user
mysql -u root -p
GRANT ALL PRIVILEGES ON database_name.* TO 'database_user'@'localhost';
FLUSH PRIVILEGES;

Step 4: Check Database Exists

mysql -e "SHOW DATABASES;" | grep database_name

Step 5: Disk Full

df -h
df -i  # Inodes full?

Step 6: Check MySQL Port/Host

# If DB_HOST not localhost, ensure port is open
# Try using IP instead
define( 'DB_HOST', '127.0.0.1' );

Step 7: Repair Database

# Add to wp-config.php
define('WP_ALLOW_REPAIR', true);

# Visit http://yourdomain.com/wp-admin/maint/repair.php
# Remove line after repair

Step 8: Check for Corrupted Tables

mysqlcheck -u root -p --auto-repair --all-databases