How to Fix 'Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock'?

Introduction

When you encounter the error message "Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock' (2)," it means there is a problem connecting to your MySQL database server. This error can occur for various reasons, including an incorrect path to the mysqld.sock file, a misconfiguration in your MySQL setup, or problems with file and directory permissions.

Whatever the cause may be, it is important that you fix this error as soon as possible, especially if you rely on your database for critical business operations. If you ignore this error or fail to fix it quickly enough, it could lead to significant disruptions in your daily operations.

An Explanation of the Error Message

The specific error message "Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock' (2)" provides some clues about what is causing the issue. In general terms, it means that something is preventing your computer from establishing a connection with the MySQL server using its default Unix socket (which is represented by /var/run/mysqld/mysqld.sock).

The "socket" refers specifically to an endpoint where two processes communicate over a network or locally via interprocess communication (IPC). When this error message occurs, it is generally a sign that the MySQL server is not running or that there is an issue with the connection between your computer and the server.

In most cases, the problem can be resolved by checking to see if the MySQL server is running, ensuring that the mysqld.sock file exists in the specified directory, and restarting both the server and your computer if necessary. In more advanced cases where those steps are unsuccessful, additional troubleshooting may be required to identify and fix deeper issues with your setup.

Understanding the Error Message

What is a socket?

A socket is a communication endpoint that allows two different processes to communicate with each other. In the context of MySQL, the mysqld.sock file serves as a local communication endpoint between the MySQL server and client applications running on the same machine.

What does "Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock' (2)" mean?

This error message indicates that the client application was unable to establish a connection with the MySQL server via its UNIX socket, which is typically located at /var/run/mysqld/mysqld.sock. Instead of connecting successfully, it encountered an error with exit code 2.

Common causes of the error

There are several possible reasons why this error might occur. One common cause is that the MySQL server process is not running or has stopped unexpectedly, so there is no socket available for client connections to use.

Another possibility is that there are permission issues with either the mysqld.sock file or its parent directory, preventing clients from accessing it properly. Other potential causes include incorrect configuration settings for either MySQL or client applications, as well as network connectivity issues.

For example, if you are attempting to connect from a remote client machine, firewalls or other network security measures may be blocking your connection attempts. It's important to thoroughly investigate all possible causes in order to effectively diagnose and resolve this error message.

Troubleshooting Steps

Check if MySQL server is running

The first step in troubleshooting the "Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock' (2)" error is to check if the MySQL server is running. This can be done by running the following command in a terminal window −

sudo systemctl status mysql 

If the output shows that the server is not active or running, start it by using this command −

sudo systemctl start mysql 

Check if mysqld.sock file exists in specified directory

If the MySQL server is up and running, then next step is to check if mysqld.sock file exists in /var/run/mysqld/ directory. To do this, run −

ls /var/run/mysqld/ 

If you cannot see the mysqld.sock file in this directory, it means that there was an issue with MySQL starting up. You will need to stop and restart MySQL.

Restart MySQL server and check again

To restart MySQL, use the following commands −

sudo systemctl stop mysql 
sudo systemctl start mysql 

Then run

ls

command again on /var/run/mysqld/ directory to see if mysqld.sock has been created.

Check permissions for mysqld.sock file and directory

The next step is to verify that both the /var/run/mysqld/ directory and mysqld.sock file have proper permissions set. Run this command to check permissions of all files in /var/run/mysqld/ −

ls -la /var/run/mysqld/ 

Permissions for both directories and files should be set at 755 as well as owned by the 'mysql' user. If these are not the permission settings, run the following commands to make changes −

sudo chmod 755 /var/run/mysqld/ 
sudo chown mysql:mysql /var/run/mysqld/ 
sudo chmod 755 /var/run/mysqld/mysqld.sock 
sudo chown mysql:mysql /var/run/mysqld/mysqld.sock 

Edit MySQL configuration file to specify correct path for mysqld.sock file

If all of the above steps did not work, then it's possible that MySQL is looking for mysqld.sock file in a different directory. In this case, you will need to modify the MySQL configuration file (my.cnf). Use your favorite text editor (vim, nano) to edit my.cnf and look for this line −

socket = /tmp/mysql.sock 

Change it to −

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

Once you've made this change, save and exit the file.

Then restart your MySQL server using

sudo systemctl restart mysql

command. If everything worked as expected, you should now be able to connect to your local MySQL server without any issues.

Advanced Troubleshooting Techniques

Using netstat command to check if port 3306 is open and listening for connections

The netstat command is a useful tool for troubleshooting connectivity issues with MySQL server. Specifically, it can be used to check if the default MySQL port (3306) is open and listening for connections.

To use the netstat command, open a terminal window and type "netstat -an | grep 3306". The output will show all connections established on port 3306 or the status of that port if it's not in use.

If there are no entries listed, then it indicates that MySQL server is not running or that there may be a firewall blocking incoming traffic on the port. If netstat shows that the port is in use but you still cannot connect to MySQL server, then it's possible that there may be other issues such as network misconfiguration or improper permissions.

Checking system logs for any related errors or warnings

Checking system logs can help identify any underlying issues causing "Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock' (2)" error messages. These logs contain important information about system events and errors, including MySQL-specific logs. Typically, log files are located in /var/log/ directory on Linux systems.

Check for any errors or warnings related to mysqld process by typing "tail -f /var/log/syslog" into your terminal window. This command will display any recent log entries as they occur; making it easy to spot issues as they arise.

Conclusion

The error "Can't connect to local MySQL server through socket 'var/run/mysqld/mysqld.sock' (2)" can be frustrating for MySQL users. However, by following the troubleshooting steps outlined in this article, you should be able to fix the issue quickly and easily.

To recap, first ensure that your MySQL server is running correctly and that the mysqld.sock file exists in the specified directory. If it doesn't exist or is not accessible, restart your MySQL server and check again.