<h2>Understanding the Core Issue</h2>
<p>When working with multiple MySQL instances on a single machine, developers often encounter situations where the <code>mysql</code> command-line client seems to ignore the specified <code>--port</code> parameter. This typically manifests when trying to connect to secondary instances while the client persistently defaults to the standard port 3306.</p>

<h2>Common Causes of Port Ignorance</h2>
<p>The <code>mysql</code> client might bypass your specified port for several reasons:</p>
<ul>
  <li>The <code>--host=localhost</code> parameter triggers Unix socket connections on Linux/Unix systems</li>
  <li>Configuration files (<code>my.cnf</code>) overriding command-line parameters</li>
  <li>Improper parameter ordering in the command syntax</li>
  <li>Typographical errors in the port specification</li>
</ul>

<h2>Solutions for Force TCP Connection</h2>
<p>To explicitly force TCP connection instead of Unix socket:</p>
<pre><code>mysql --protocol=TCP --host=127.0.0.1 --port=9999 -u root -p
</code></pre>

<p>Key differences from original command:</p>
<ul>
  <li><code>--protocol=TCP</code> explicitly requests TCP connection</li>
  <li><code>127.0.0.1</code> instead of <code>localhost</code> prevents socket fallback</li>
</ul>

<h2>Verifying Active Connections</h2>
<p>To confirm which port your client is actually using:</p>
<pre><code>mysqladmin --host=127.0.0.1 --port=9999 processlist
</code></pre>

<h2>Configuration File Precedence</h2>
<p>Check for conflicting settings in configuration files:</p>
<pre><code>mysql --print-defaults
</code></pre>
<p>This reveals all parameters loaded from configuration files that might override your command-line arguments.</p>

<h2>Debugging Connection Attempts</h2>
<p>For detailed connection diagnostics:</p>
<pre><code>mysql --verbose --host=127.0.0.1 --port=9999
</code></pre>
<p>The <code>--verbose</code> flag provides detailed connection attempt information.</p>

<h2>Alternative Connection Methods</h2>
<p>If port specification still fails, consider:</p>
<pre><code># Using the TCP syntax shortcut
mysql -h 127.0.0.1 -P 9999 -u root -p

# Specifying the socket explicitly for socket connections
mysql --socket=/path/to/mysql.sock -u root -p
</code></pre>



When working with multiple MySQL instances on a single machine, developers often encounter this strange scenario:

mysql --host=localhost --port=9999 mysql -u root -p --execute="show tables;"

Despite specifying a custom port (9999 in this case), the connection consistently defaults to the standard 3306 port. This behavior persists even when:

Different port numbers are specified
The target MySQL instance is confirmed to be running on the specified port
Network connectivity is verified

The issue stems from how MySQL interprets localhost connections on Unix-like systems. When you specify:
--host=localhost

MySQL automatically uses a Unix domain socket connection instead of TCP/IP, completely bypassing your specified port. This is an optimization for local connections but causes confusion when dealing with multiple instances.
Solution 1: Force TCP/IP connection
Replace localhost with 127.0.0.1 to ensure TCP/IP connection:
mysql --host=127.0.0.1 --port=9999 -u root -p

Solution 2: Specify the socket explicitly
If you must use Unix sockets, specify the correct socket path:
mysql --socket=/path/to/mysql2.sock -u root -p

Solution 3: Verify with netstat
First confirm your MySQL instance is actually listening on the expected port:
netstat -tulnp | grep mysql

For a development environment with two MySQL instances (3306 and 3307), here's how to properly connect:
# First instance (default)
mysql --host=127.0.0.1 --port=3306 -u root -p

# Second instance
mysql --host=127.0.0.1 --port=3307 -u root -p

For permanent solutions, consider these approaches:
1. Create client configuration files:
[client]
host=127.0.0.1
port=3307
user=dev_user

2. Use connection aliases in ~/.my.cnf:
[client1]
host=127.0.0.1
port=3306

[client2]
host=127.0.0.1
port=3307

Then connect using:
mysql --defaults-group-suffix=2