Fix common MySQL connection errors
Common connection errors
MySQL connection errors can have several causes. This guide helps you identify and fix the most frequent problems.
Error 1: "Can't connect to MySQL server"
Possible causes:
- MySQL is not running
- Port blocked by firewall
- Incorrect IP address or host
- MySQL is not listening on the correct interface
Solutions:
1. Verify MySQL is running:
sudo systemctl status mysql
# Or
sudo systemctl status mysqld
If not running, start it:
sudo systemctl start mysql
sudo systemctl enable mysql
2. Verify MySQL is listening:
sudo netstat -tlnp | grep 3306
# Or
sudo ss -tlnp | grep 3306
You should see something like: 0.0.0.0:3306 or 127.0.0.1:3306
3. Check firewall:
sudo ufw status
sudo ufw allow 3306/tcp
4. Check bind-address configuration:
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf
Verify that bind-address is configured correctly: - 127.0.0.1 for local connections only - 0.0.0.0 for remote connections
Error 2: "Access denied for user"
Possible causes:
- Incorrect password
- User doesn't exist
- User doesn't have permissions to connect from that host
Solutions:
1. Verify credentials:
mysql -u user -p
If it works from terminal but not from application, the problem may be in application configuration.
2. Verify user exists:
mysql -u root -p
SELECT user, host FROM mysql.user WHERE user='username';
3. Verify user permissions:
SHOW GRANTS FOR 'user'@'localhost';
SHOW GRANTS FOR 'user'@'%';
4. Grant permissions if necessary:
GRANT ALL PRIVILEGES ON database_name.* TO 'user'@'localhost';
FLUSH PRIVILEGES;
Error 3: "Too many connections"
Cause: Maximum limit of simultaneous connections reached.
Solutions:
1. See current connections:
mysql -u root -p
SHOW PROCESSLIST;
SHOW STATUS LIKE 'Threads_connected';
2. See maximum limit:
SHOW VARIABLES LIKE 'max_connections';
3. Increase connection limit:
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf
Add or modify:
[mysqld]
max_connections = 200
Restart MySQL:
sudo systemctl restart mysql
4. Close inactive connections:
mysql -u root -p
KILL process_id;
Error 4: "Connection refused"
Possible causes:
- MySQL is not running
- Incorrect port
- Firewall blocking the port
Solutions:
1. Verify MySQL is running:
sudo systemctl status mysql
2. Verify port:
mysql -u root -p -e "SHOW VARIABLES LIKE 'port';"
3. Check firewall:
sudo ufw status
sudo iptables -L -n | grep 3306
Error 5: "Host is not allowed to connect"
Cause: The host you're trying to connect from is not allowed.
Solutions:
1. See allowed hosts:
mysql -u root -p
SELECT user, host FROM mysql.user WHERE user='username';
2. Allow connection from any host (less secure):
GRANT ALL PRIVILEGES ON database_name.* TO 'user'@'%' IDENTIFIED BY 'password';
FLUSH PRIVILEGES;
3. Allow connection from specific IP (more secure):
GRANT ALL PRIVILEGES ON database_name.* TO 'user'@'192.168.1.100' IDENTIFIED BY 'password';
FLUSH PRIVILEGES;
Error 6: "Unknown database"
Cause: The specified database doesn't exist.
Solutions:
1. List available databases:
mysql -u root -p
SHOW DATABASES;
2. Create database if it doesn't exist:
CREATE DATABASE database_name CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci;
3. Verify name in configuration:
Check that the database name in your application is correct (case-sensitive on Linux).
Error 7: "Lost connection to MySQL server"
Possible causes:
- Connection timeout
- MySQL restarted
- Network problems
- Very long query
Solutions:
1. Increase timeout:
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf
Add:
[mysqld]
wait_timeout = 600
interactive_timeout = 600
2. Check MySQL logs:
sudo tail -f /var/log/mysql/error.log
3. Check MySQL status:
sudo systemctl status mysql
Error 8: "SSL connection error"
Cause: Problem with SSL configuration.
Solutions:
1. Disable SSL verification (development only):
In connection, add: ?ssl-mode=DISABLED
2. Configure SSL correctly:
mysql -u root -p
SHOW VARIABLES LIKE '%ssl%';
Diagnostic tools
1. Test connection from terminal:
mysql -h localhost -u user -p
mysql -h 127.0.0.1 -u user -p
mysql -h SERVER_IP -u user -p
2. Verify network connectivity:
telnet SERVER_IP 3306
# Or
nc -zv SERVER_IP 3306
3. See MySQL logs:
sudo tail -f /var/log/mysql/error.log
sudo tail -f /var/log/mysql/mysql.log
4. See MySQL processes:
mysql -u root -p
SHOW PROCESSLIST;
SHOW STATUS;
Troubleshooting checklist
- ✅ Verify MySQL is running
- ✅ Verify credentials (username and password)
- ✅ Verify database exists
- ✅ Verify user permissions
- ✅ Verify firewall configuration
- ✅ Verify bind-address configuration
- ✅ Verify MySQL logs
- ✅ Verify network connectivity
- ✅ Verify connection limits
Problem prevention
- Monitor connections: Regularly check how many connections are active
- Use persistent connections: In web applications, use connection pooling
- Close connections correctly: Make sure to close connections when not in use
- Configure appropriate timeouts: Avoid very short or very long timeouts
- Make regular backups: To be able to restore if there are problems
Need help?
If you can't resolve the connection error, open a ticket from the billing.baires.host panel or contact us for support. Include complete error messages and steps you've already tried.
You can also reach us through our social media:
- Instagram: @baires_host
- Discord (active support): https://discord.gg/dzjauatAFN
- Linktree: https://linktr.ee/baires.host
