How to fix ERROR 2003 (HY000): Can't connect to MySQL server on host in MySQL

Check if the MySQL daemon is active on the target host.

On Linux/macOS:

# Check service status
sudo systemctl status mysql
# or
sudo service mysql status

# If not running, start it
sudo systemctl start mysql
# or
sudo service mysql start

On Windows:
Open Services (services.msc) and look for "MySQL" or "MySQL80" service. If Status is blank, right-click and select "Start".

Verify with telnet:

telnet hostname_or_ip 3306

If connection succeeds, you'll see MySQL server version info. If it fails with "Connection refused" or timeout, MySQL is not listening.

Use telnet or nc (netcat) to verify network connectivity to the MySQL port:

# Test with telnet (install if needed: apt install telnetd)
telnet 192.168.1.100 3306

# Test with nc
nc -zv 192.168.1.100 3306

# Test DNS resolution (if using hostname instead of IP)
nslookup mysql.example.com
dig mysql.example.com

If telnet connects, you'll see a prompt with MySQL version. If it fails with "Connection refused" or timeout after 30 seconds, either the port is blocked or MySQL isn't listening.

If MySQL is running but you can't connect remotely, verify the bind-address setting.

View current configuration:

-- Connect locally (if possible)
mysql -u root
SHOW VARIABLES LIKE 'bind_address';

Edit MySQL configuration file:
Find the configuration file (usually /etc/mysql/my.cnf, /etc/mysql/mysql.conf.d/mysqld.cnf, or /etc/my.cnf):

# For localhost-only connections (default):
[mysqld]
bind-address = 127.0.0.1

# For all interfaces:
[mysqld]
bind-address = 0.0.0.0

# For specific hostname/IP:
[mysqld]
bind-address = 192.168.1.100

After editing, restart MySQL:

sudo systemctl restart mysql

Ensure you're using the correct hostname, IP address, and port:

# Connect with explicit parameters
mysql -h 192.168.1.100 -P 3306 -u root -p

# For remote host (verify IP is correct)
mysql -h remote-server.example.com -u root -p

# Find MySQL listening port
sudo netstat -tlnp | grep mysql
# or
sudo ss -tlnp | grep mysql

Ensure the hostname/IP resolves to the correct server and the port matches MySQL's listening port (default 3306).

Firewall rules must explicitly allow port 3306 from client hosts.

On Linux with UFW:

# Allow MySQL from any host
sudo ufw allow 3306/tcp

# Allow MySQL from specific IP
sudo ufw allow from 192.168.1.50 to any port 3306

# Check rules
sudo ufw status

On Linux with iptables:

# Allow MySQL connections
sudo iptables -A INPUT -p tcp --dport 3306 -j ACCEPT
sudo iptables-save > /etc/iptables/rules.v4

On Windows Firewall:
Go to Windows Defender Firewall → Advanced Settings → Inbound Rules → New Rule. Create rule allowing TCP port 3306.

On AWS Security Groups/Azure NSGs:
Add inbound rule allowing TCP port 3306 from your client IP address.

If MySQL was started with skip-networking enabled, no TCP/IP connections are accepted.

Check if skip-networking is active:

SHOW VARIABLES LIKE 'skip_networking';

If the value is ON, disable it in the configuration file:

[mysqld]
# Comment out or remove this line
# skip-networking

Then restart MySQL:

sudo systemctl restart mysql

Alternatively, connect via Unix socket if available:

mysql -u root --socket=/tmp/mysql.sock

For local connections on Unix-based systems, MySQL can use sockets instead of TCP/IP.

Check socket location:

# Default socket locations
ls -la /tmp/mysql.sock
ls -la /var/run/mysqld/mysqld.sock

Connect using socket:

mysql -u root --socket=/tmp/mysql.sock

If socket is missing or inaccessible:
Restart MySQL to regenerate the socket:

sudo systemctl restart mysql

If a cron job removes old files from /tmp, configure MySQL to use a persistent socket location in /var/run/mysqld/ instead.

If connecting using a hostname instead of IP address, ensure DNS resolution works:

# Test DNS resolution
nslookup mysql.example.com
dig mysql.example.com
host mysql.example.com

# Test with IP instead to isolate DNS issues
mysql -h 192.168.1.100 -u root -p

# If IP works but hostname doesn't, it's a DNS issue
# Update /etc/hosts as a temporary workaround
echo "192.168.1.100 mysql.example.com" | sudo tee -a /etc/hosts

If DNS resolution fails, contact your network administrator or update DNS records pointing the hostname to the correct MySQL server IP.