How to fix CR_IPSOCK_ERROR (2004): Can't create TCP/IP socket in MySQL

# Check current file descriptor limits for the process
cat /proc/$(pgrep -f "your-app-process")/limits | grep "open files"

# Check system-wide limits
ulimit -n
ulimit -Sn  # Soft limit
ulimit -Hn  # Hard limit

# Check kernel limits
cat /proc/sys/fs/file-max
cat /proc/sys/fs/file-nr

# Increase limits temporarily
ulimit -n 65536

# Permanent increase in /etc/security/limits.conf
* soft nofile 65536
* hard nofile 65536

# For systemd services, add to service file:
[Service]
LimitNOFILE=65536

# Reload systemd and restart service
sudo systemctl daemon-reload
sudo systemctl restart your-service

# Test basic network connectivity to MySQL server
ping mysql-server-hostname
nc -zv mysql-server-hostname 3306

# Check local network stack
ip addr show
ip route show

# Check firewall rules (iptables)
sudo iptables -L -n -v
sudo iptables -L -n -v | grep 3306

# Check nftables
sudo nft list ruleset

# Check if port 3306 is blocked
sudo ss -tlnp | grep 3306

# Temporarily disable firewall to test (not for production)
sudo systemctl stop firewalld
# or
sudo ufw disable

# For Docker/container environments, check network mode:
docker inspect container-name | grep -A 10 "NetworkSettings"

# Ensure container has network access
docker run --network host ...  # For host network mode

# Check current kernel parameters
cat /proc/sys/net/core/somaxconn
cat /proc/sys/net/ipv4/tcp_max_syn_backlog
cat /proc/sys/net/core/netdev_max_backlog

# Check ephemeral port range
cat /proc/sys/net/ipv4/ip_local_port_range

# Increase socket-related parameters temporarily
sudo sysctl -w net.core.somaxconn=1024
sudo sysctl -w net.ipv4.tcp_max_syn_backlog=2048
sudo sysctl -w net.core.netdev_max_backlog=2000

# Increase ephemeral port range
sudo sysctl -w net.ipv4.ip_local_port_range="1024 65535"

# Make permanent changes in /etc/sysctl.conf
net.core.somaxconn = 1024
net.ipv4.tcp_max_syn_backlog = 2048
net.core.netdev_max_backlog = 2000
net.ipv4.ip_local_port_range = 1024 65535

# Apply changes
sudo sysctl -p

# Check total available sockets
cat /proc/sys/net/ipv4/tcp_mem
cat /proc/sys/net/ipv4/tcp_rmem
cat /proc/sys/net/ipv4/tcp_wmem

# Check SELinux status
getenforce
sestatus

# Check for SELinux denials related to MySQL or sockets
sudo ausearch -m avc -ts recent | grep -i socket
sudo ausearch -m avc -ts recent | grep -i mysql

# Check audit logs
sudo grep -i "socket" /var/log/audit/audit.log
sudo grep -i "mysql" /var/log/audit/audit.log

# Temporarily disable SELinux to test (not for production)
sudo setenforce 0

# Check AppArmor status (Ubuntu/Debian)
sudo aa-status
sudo aa-status | grep mysql

# Check AppArmor profiles
sudo apparmor_status

# Temporarily disable AppArmor for MySQL
sudo aa-complain /usr/sbin/mysqld
sudo aa-complain /usr/bin/mysql

# Check capabilities
getcap $(which mysql)
getcap $(which mysqld)

# Add network capability if needed (advanced)
sudo setcap 'cap_net_bind_service,cap_net_admin+ep' /usr/bin/mysql

# MySQL command line - use UNIX socket instead of TCP/IP
mysql -u username -p  # Uses default socket

# Specify socket explicitly
mysql --socket=/var/run/mysqld/mysqld.sock -u username -p

# In application configuration, use socket instead of host:port

// PHP - Use socket instead of TCP/IP
// Instead of: mysql:host=127.0.0.1;port=3306
// Use:
$dsn = "mysql:unix_socket=/var/run/mysqld/mysqld.sock;dbname=mydatabase";

# Python - Use socket
import mysql.connector

config = {
    'unix_socket': '/var/run/mysqld/mysqld.sock',
    'user': 'username',
    'password': 'password',
    'database': 'mydb'
}

// Node.js - Use socket
const mysql = require('mysql2/promise');

const connection = await mysql.createConnection({
  socketPath: '/var/run/mysqld/mysqld.sock',
  user: 'root',
  password: 'password',
  database: 'mydb'
});

# Check system memory usage
free -h

# Check swap usage
swapon --show

# Check process limits
cat /proc/$(pidof mysqld)/limits
cat /proc/$(pidof your-app)/limits

# Check number of open files system-wide
cat /proc/sys/fs/file-nr
# Output format: allocated unused maximum

# Check for out-of-memory conditions
dmesg | grep -i "out of memory"
dmesg | grep -i "oom"

# Check kernel messages for socket errors
dmesg | grep -i "socket"
dmesg | grep -i "tcp"

# Check network connection count
ss -s

# Check for TIME_WAIT sockets (can exhaust ports)
ss -tan state time-wait | wc -l

# Reduce TIME_WAIT timeout (temporary fix)
sudo sysctl -w net.ipv4.tcp_fin_timeout=30
sudo sysctl -w net.ipv4.tcp_tw_reuse=1
sudo sysctl -w net.ipv4.tcp_tw_recycle=1  # Careful with NAT

# Monitor socket creation with strace
strace -e socket,connect your-application-command 2>&1 | grep -i "socket\|failed"