MySQL ERROR 2002 (HY000): Can't connect to local MySQL server through socket

Symptoms

When trying to connect to MySQL locally, you receive the following error:

ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

This error prevents any MySQL client (mysql, phpMyAdmin, etc.) from connecting to the database server. The error may also appear in application logs, causing website or service downtime.

Root Causes

• MySQL service not running: The MySQL daemon (mysqld) has stopped or failed to start.
• Socket file missing or deleted: The Unix socket file (usually /var/run/mysqld/mysqld.sock or /tmp/mysql.sock) does not exist.
• Incorrect socket path in client configuration: The MySQL client is looking for the socket in the wrong location.
• File permissions: The MySQL user does not have permission to access the socket directory.
• Disk space full: The partition containing the socket directory is full.
• Corrupted MySQL installation or configuration: Damaged configuration files or missing dependencies.

Step-by-Step Fix

1. Check if MySQL Service is Running

Run the following command to check the MySQL service status:

systemctl status mysql

Or for older systems:

service mysql status

If the service is not active, start it:

systemctl start mysql

2. Verify the Socket File Exists

Check the default socket location:

ls -la /var/run/mysqld/mysqld.sock

If the file is missing, the MySQL service may not have created it. Restart the service:

systemctl restart mysql

3. Check MySQL Error Log

View the MySQL error log to identify why the service failed to start:

tail -50 /var/log/mysql/error.log

Look for errors like Can't start server: Bind on Unix socket or permission issues.

4. Verify MySQL Configuration

Open the MySQL configuration file:

nano /etc/mysql/my.cnf

Ensure the socket directive is set correctly under the [mysqld] section:

[mysqld]
socket = /var/run/mysqld/mysqld.sock

Also check the [client] section for the same socket path:

[client]
socket = /var/run/mysqld/mysqld.sock

5. Check Socket Directory Permissions

Ensure the MySQL user owns the socket directory:

chown mysql:mysql /var/run/mysqld
chmod 755 /var/run/mysqld

6. Test Connection with Explicit Socket

Try connecting directly specifying the socket:

mysql -u root -p -S /var/run/mysqld/mysqld.sock

If this works, the socket path in your client configuration is incorrect.

7. Restart MySQL Service

After making changes, restart MySQL:

systemctl restart mysql

Alternative Fixes

• Use TCP/IP connection: Connect via localhost using TCP instead of socket: mysql -u root -p -h 127.0.0.1
• Reinstall MySQL: If the socket file is persistently missing, reinstall MySQL: apt-get remove --purge mysql-server mysql-client then apt-get install mysql-server mysql-client
• Check disk space: Run df -h to ensure the partition is not full.
• Check AppArmor/SELinux: Disable or adjust security modules that may block socket creation.

Prevention

• Monitor MySQL service: Use monitoring tools (Nagios, Zabbix) to alert when MySQL is down.
• Regular backups: Keep configuration file backups.
• Update regularly: Keep MySQL updated to avoid bugs.
• Document socket path: Ensure all applications use the correct socket path.
• Automated health checks: Schedule cron jobs to verify MySQL connectivity.

Conclusion

MySQL ERROR 2002 (HY000) is usually resolved by restarting the MySQL service or fixing the socket path configuration. By following the steps above, you can quickly restore database connectivity.