What's Actually Happening

When you get a MySQL connection refused error, the client cannot establish a TCP connection to the MySQL server. This means the server isn't listening on the expected host and port, or network issues block the connection.

The Error You'll See

```bash $ mysql -u root -p ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

# Or for TCP connection: ERROR 2003 (HY000): Can't connect to MySQL server on '127.0.0.1:3306' (111) ```

Why This Happens

  1. 1.MySQL not running - Server stopped or crashed
  2. 2.Wrong host/port - MySQL listening elsewhere
  3. 3.Socket file missing - Unix socket deleted
  4. 4.Bind address - MySQL only on localhost, not remote
  5. 5.Firewall - Port 3306 blocked
  6. 6.Permission denied - Socket file permissions

Step 1: Check MySQL Service Status

bash
# Check if MySQL is running
systemctl status mysql
# Or:
systemctl status mysqld
# Or:
systemctl status mariadb

If not running:

bash
systemctl start mysql
systemctl enable mysql

Step 2: Check MySQL Process

bash
ps aux | grep mysql

Should show mysqld process:

bash
mysql    1234  0.5  5.0 1234567 123456 ?      Ssl  10:00   0:01 /usr/sbin/mysqld

Step 3: Check MySQL Port

bash
# Check if MySQL is listening
netstat -tlnp | grep mysql
# Or:
ss -tlnp | grep mysql

Output:

bash
tcp  0  0 127.0.0.1:3306  0.0.0.0:*  LISTEN  1234/mysqld

If empty, MySQL not listening on any port.

Step 4: Check MySQL Socket

```bash # Find socket location mysqladmin -u root variables | grep socket

# Check socket exists ls -la /var/run/mysqld/mysqld.sock # Or: ls -la /tmp/mysql.sock ```

If missing:

bash
# Restart MySQL to recreate socket
systemctl restart mysql

Step 5: Check MySQL Bind Address

bash
# Check config
grep bind-address /etc/mysql/mysql.conf.d/mysqld.cnf

Default:

bash
bind-address = 127.0.0.1

This only accepts localhost connections.

To allow remote connections:

```bash sudo vim /etc/mysql/mysql.conf.d/mysqld.cnf

# Change to: bind-address = 0.0.0.0

# Restart systemctl restart mysql ```

Step 6: Test Local Connection

```bash # Connect via socket mysql -u root -p --socket=/var/run/mysqld/mysqld.sock

# Connect via TCP mysql -u root -p -h 127.0.0.1 -P 3306 ```

Step 7: Check Firewall

For remote connections:

```bash # Check firewall sudo iptables -L -n | grep 3306

# For ufw sudo ufw status

# Allow MySQL port sudo ufw allow 3306/tcp

# For firewalld sudo firewall-cmd --add-port=3306/tcp --permanent sudo firewall-cmd --reload ```

Step 8: Check MySQL Error Log

bash
tail -f /var/log/mysql/error.log

Look for errors:

bash
Can't start server: Bind on TCP/IP port: Address already in use
Can't create IP socket: Permission denied
Fatal error: Can't open and lock privilege tables

Step 9: Check Disk Space

bash
df -h /var/lib/mysql

If disk full, MySQL can't start:

bash
# Free space
rm /var/log/mysql/old-logs
# Or increase disk size

Step 10: Check Data Directory Permissions

bash
ls -la /var/lib/mysql

Should be owned by mysql user:

bash
drwxr-xr-x  mysql mysql  /var/lib/mysql

Fix:

bash
chown -R mysql:mysql /var/lib/mysql
chmod 750 /var/lib/mysql

Verify the Fix

```bash # Test connection mysql -u root -p -e "SELECT 1;"

# Check server responds mysqladmin -u root -p ping # mysqld is alive

# Test from remote host mysql -u root -p -h mysql-server-ip -P 3306 ```

Prevention Tips

```bash # Enable MySQL to start on boot systemctl enable mysql

# Monitor MySQL health mysqladmin -u root -p status

# Set up alerts # Prometheus: mysql_up == 0 ```