Fix PHP Warning: mysqli_connect(): (HY000/2002): No such file or directory When Using localhost

What's Actually Happening

MySQL is running. PHP is installed. Your connection string looks fine. Then your script fires and you get this:

Warning: mysqli_connect(): (HY000/2002): No such file or directory

The "file or directory" PHP can't find isn't your PHP script or your config. It's a Unix socket file — the communication channel MySQL uses when you connect via localhost.

One thing trips people up here: passing localhost to mysqli_connect() doesn't use TCP/IP. PHP skips the network stack entirely and looks for a Unix domain socket on the filesystem. If PHP expects the socket at /tmp/mysql.sock but MySQL put it at /var/run/mysqld/mysqld.sock, you get this error every time.

Debug: Find Where the Socket Actually Is

Start by confirming MySQL is running:

sudo systemctl status mysql
# or for MariaDB:
sudo systemctl status mariadb

Not running? Start it and you're done. Still running? The socket path mismatch is your culprit. Find the real socket location:

mysql -u root -p -e "SHOW VARIABLES LIKE 'socket';"

Example output:

+---------------+--------------------------+
| Variable_name | Value                    |
+---------------+--------------------------+
| socket        | /var/run/mysqld/mysqld.sock |
+---------------+--------------------------+

Now check what PHP thinks the socket path should be:

php -r "echo ini_get('mysqli.default_socket');"

Or search directly in php.ini:

grep -r "mysqli.default_socket" /etc/php/

Different paths? That's your problem. Same paths but the socket file doesn't exist on disk? MySQL isn't running, or it crashed on startup.

Solution 1: Use 127.0.0.1 Instead of localhost (Quickest Fix)

Swap localhost for 127.0.0.1. No config changes, no restarts — just one character difference that completely changes how PHP connects:

<?php
// Before (uses Unix socket — breaks if socket path is wrong)
$conn = mysqli_connect('localhost', 'myuser', 'mypass', 'mydb');

// After (forces TCP/IP — bypasses the socket issue entirely)
$conn = mysqli_connect('127.0.0.1', 'myuser', 'mypass', 'mydb');
?>

With 127.0.0.1, PHP connects over TCP on port 3306. MySQL listens there by default, so this works immediately on most setups.

Using PDO? Same swap:

<?php
$pdo = new PDO('mysql:host=127.0.0.1;port=3306;dbname=mydb', 'myuser', 'mypass');
?>

Solution 2: Fix the Socket Path in php.ini (Proper Fix)

If you can't change the connection code — say, it's a legacy app or a CMS you don't control — align PHP's socket setting with where MySQL actually put it.

First, find your active php.ini:

php --ini | grep "Loaded Configuration"

Open that file and update all three socket settings to match the path from SHOW VARIABLES LIKE 'socket':

; In php.ini
mysqli.default_socket = /var/run/mysqld/mysqld.sock
pdo_mysql.default_socket = /var/run/mysqld/mysqld.sock
mysql.default_socket = /var/run/mysqld/mysqld.sock

Then restart your PHP process:

# For PHP-FPM:
sudo systemctl restart php8.1-fpm

# For Apache with mod_php:
sudo systemctl restart apache2

Solution 3: Pass the Socket Explicitly in Your Code

Rather than relying on php.ini defaults, hardcode the socket path directly in mysqli_connect(). Useful when you need one connection to use a socket and others to use TCP:

<?php
$conn = mysqli_connect(
    'localhost',
    'myuser',
    'mypass',
    'mydb',
    3306,
    '/var/run/mysqld/mysqld.sock'  // explicit socket path
);
?>

OOP style:

<?php
$mysqli = new mysqli();
$mysqli->real_connect(
    'localhost',
    'myuser',
    'mypass',
    'mydb',
    3306,
    '/var/run/mysqld/mysqld.sock'
);
?>

Common Socket Paths by System

Socket locations vary by distro and MySQL variant. Here's where to look:

• Ubuntu/Debian (MySQL): /var/run/mysqld/mysqld.sock
• CentOS/RHEL (MySQL): /var/lib/mysql/mysql.sock
• MariaDB (most distros): /var/run/mysqld/mysqld.sock or /tmp/mysql.sock
• MAMP/XAMPP (macOS): /Applications/MAMP/tmp/mysql/mysql.sock
• Homebrew MySQL (macOS): /tmp/mysql.sock

When in doubt, run SHOW VARIABLES LIKE 'socket' — MySQL always knows where it put the file.

Verify the Fix

Test from the command line before touching your app:

php -r "
\$conn = mysqli_connect('127.0.0.1', 'myuser', 'mypass', 'mydb');
if (\$conn) {
    echo 'Connected successfully\n';
    mysqli_close(\$conn);
} else {
    echo 'Error: ' . mysqli_connect_error() . '\n';
}
"

Or drop this temporary block into your app to see the server version on success:

<?php
$conn = mysqli_connect('127.0.0.1', 'myuser', 'mypass', 'mydb');
if (!$conn) {
    die('Connection failed: ' . mysqli_connect_error());
}
echo 'Connected. MySQL server version: ' . mysqli_get_server_info($conn);
mysqli_close($conn);
?>

Key Takeaways

• localhost and 127.0.0.1 are not interchangeable in PHP database connections. One hits a Unix socket file; the other goes over TCP/IP.
• "No such file or directory" is a filesystem error, not a network error. PHP literally can't find the socket file at the path it expects.
• Switching between MySQL and MariaDB, or moving between distros, often changes the socket path. Always recheck.
• In Docker containers or mixed environments where socket paths shift, 127.0.0.1 is the more portable choice — it doesn't depend on any file existing on disk.