Database Error: SQLSTATE[HY000] [2002] Can't connect to local server through socket '/var/lib/mysql/mysql.sock' (111)

The error message "Database Error: SQLSTATE[HY000] [2002] Can't connect to local server through socket '/var/lib/mysql/mysql.sock' (111)" typically occurs when there is an issue with accessing the MySQL or MariaDB database server. The error message indicates that the server failed to connect through the specified socket file.

Here are common reasons for this error and potential solutions:

Database Server Not Running: The MySQL or MariaDB server may not be running. Try restarting the server using command-line tools (on Linux) or through service management tools (on Windows).
MySQL Socket File Access Issue: There may be a permission issue with the socket file that MySQL or MariaDB is trying to use. Ensure that the socket file exists and has the correct permissions.
Check if MySQL Service is Running: Make sure that the MySQL service is running. You can check this using system management commands, such as "systemctl status mysql" or "systemctl status mariadb" on Linux.
MySQL Server Connection Settings: Verify that your web application or any software connecting to the MySQL server has the correct connection settings. Ensure that you are using the correct server hostname ("localhost" or "127.0.0.1"), and the right username and password.
MySQL Server Port Settings: Check that the MySQL server is configured to use the correct connection port. Typically, it uses port 3306.
Firewall Issues: If you have a firewall on your server, make sure it allows incoming connections to the MySQL port. Review any firewall rules that might be blocking connections.
Other Factors: There could be other factors at play as well. For example, your server's disk space might be full, or the MySQL server could be misconfigured. In such cases, reviewing server logs for more detailed error messages is crucial.

This error is often related to one or more of the above factors. To resolve it, start by identifying the root cause and then apply the appropriate solution. If the issue persists, consider seeking further assistance from your system administrator or hosting provider.