Mastering MySQL Replication: Solving Error 1218 (ER_CONNECT_TO_MASTER)

When managing a MySQL replication setup, Error 1218 – SQLSTATE: 08S01 (ER_CONNECT_TO_MASTER) is a common roadblock that indicates a connection issue between the slave and the master server. This error can be caused by a variety of factors, from network issues to incorrect configuration settings. This guide will provide you with a structured approach to diagnose and resolve this error, ensuring a stable connection for your replication environment.

Understanding Error 1218

Error 1218 occurs when the slave server is unable to establish a connection to the master server. The %s in the error message will contain the specific error details, which can help pinpoint the exact cause of the connection failure.

Diagnosing the Error

To diagnose the error, start by examining the error message details and check the slave server’s error logs for any additional information. Also, verify the replication settings:


Look for the Last_IO_Error field, which can provide more insight into the connection issue.

Fixing the Error

Here are various scenarios that might cause Error 1218 and the corresponding solutions:

1. Network Connectivity Issues

Check if the slave can reach the master server:

ping master_host

If there is a network issue, troubleshoot the connectivity or contact your network administrator.

2. Incorrect Master Host Configuration

Ensure the master host is correctly configured on the slave:

CHANGE MASTER TO MASTER_HOST='correct_master_host';

Replace correct_master_host with the actual hostname or IP address of the master server.

3. Master Server Port Accessibility

Verify that the master server’s port is accessible from the slave:

telnet master_host master_port

If the port is not accessible, check for firewall rules or network ACLs that may be blocking the connection.

4. Incorrect Replication Credentials

Ensure the replication user and password are set correctly:

CHANGE MASTER TO MASTER_USER='replication_user', MASTER_PASSWORD='replication_password';

Replace replication_user and replication_password with the actual credentials.

5. Master Server Configuration

On the master server, check that it is configured to accept replication connections:

SHOW VARIABLES LIKE 'bind_address';
SHOW VARIABLES LIKE 'skip_networking';

Ensure bind_address is not set to and skip_networking is off.

6. Slave Server Configuration

On the slave server, confirm that the master log file and position are correctly set:

CHANGE MASTER TO MASTER_LOG_FILE='master_log_file', MASTER_LOG_POS=master_log_position;

Replace master_log_file and master_log_position with the correct values from the master server.

7. Server Identities

Both master and slave servers must have unique server IDs:


Ensure each server has a unique server_id value.

8. Master Server Running

Confirm that the master MySQL server is running and that there are no issues preventing it from accepting connections.

Preventive Measures

To prevent Error 1218:

  • Regularly monitor network connectivity between master and slave servers.
  • Keep replication settings documented and regularly review them for accuracy.
  • Ensure that firewall rules and network settings allow for uninterrupted communication between the servers.


Error 1218 can be a stumbling block in MySQL replication, but with careful troubleshooting and attention to configuration details, it can be resolved. By systematically checking each potential cause, you can re-establish a stable connection between your master and slave servers. For more comprehensive information on replication and troubleshooting, the MySQL Replication documentation is an excellent resource. If you continue to face challenges, consider reaching out to a database specialist for further assistance.

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