How to fix CR_SOCKET_CREATE_ERROR (2001): Can't create UNIX socket in MySQL

# View current limits for current shell
ulimit -n
ulimit -a

# View limits for mysqld process
cat /proc/$(pgrep mysqld)/limits | grep "open files"

# View descriptor usage
lsof -p $(pgrep mysqld) | wc -l
ls /proc/$(pgrep mysqld)/fd | wc -l

# Increase for current shell
ulimit -n 4096

# Verify change
ulimit -n

# Now try connecting to MySQL
mysql -u root -p

# Edit MySQL systemd service
sudo systemctl edit mysql

# Add or modify the [Service] section:
[Service]
LimitNOFILE=4096
LimitNPROC=4096

# Save (Ctrl+X, Y, Enter)

# Or edit limits.conf for system-wide settings
sudo nano /etc/security/limits.conf

# Add at the end:
mysql soft nofile 4096
mysql hard nofile 10240
mysql soft nproc 4096
mysql hard nproc 10240

# Apply changes
sudo systemctl daemon-reload
sudo systemctl restart mysql

# Verify new limits
cat /proc/$(pgrep mysqld)/limits | grep "open files"
ulimit -n

# Check if directory exists
ls -la /var/run/mysqld/

# If directory doesn't exist, create it
sudo mkdir -p /var/run/mysqld
sudo chown mysql:mysql /var/run/mysqld
sudo chmod 755 /var/run/mysqld

# If socket file exists but has wrong permissions
sudo ls -la /var/run/mysqld/mysqld.sock

# Fix socket file permissions
sudo chown mysql:mysql /var/run/mysqld/mysqld.sock
sudo chmod 660 /var/run/mysqld/mysqld.sock

# Verify permissions (mysql should be owner and group)
ls -la /var/run/mysqld/
# Should show: drwxr-xr-x mysql:mysql mysqld

# Check free space on /var/run
df /var/run
df -h /var/run

# Check if filesystem is mounted read-only
mount | grep "/var/run"
# Should show "rw" (read-write), not "ro" (read-only)

# If read-only, remount as read-write
sudo mount -o remount,rw /var/run

# Check for disk full globally
df -h /
du -sh /var/run

# List large files in /var/run
ls -lhS /var/run | head

# Force TCP protocol (bypass socket)
mysql -h 127.0.0.1 -u root -p --protocol=TCP

# In application connection strings
# Instead of: socket=/var/run/mysqld/mysqld.sock
# Use: host=127.0.0.1, port=3306

# PHP PDO
$dsn = "mysql:host=127.0.0.1;port=3306;dbname=mydb";

# Python
connection = mysql.connector.connect(
    host="127.0.0.1",
    port=3306,
    user="root",
    password="password"
)

# Node.js
const connection = mysql.createConnection({
  host: '127.0.0.1',
  port: 3306,
  user: 'root'
});

# View MySQL error log
sudo tail -n 100 /var/log/mysql/error.log
# or for MariaDB
sudo tail -n 100 /var/log/mariadb/mariadb.log

# Search for socket-related errors
sudo grep -i socket /var/log/mysql/error.log
sudo grep -i "too many open files" /var/log/mysql/error.log

# Watch log in real-time
sudo tail -f /var/log/mysql/error.log

# Check systemd journal for startup errors
sudo journalctl -u mysql -n 50
sudo journalctl -u mysql -f

# Look for permission or resource errors
sudo journalctl -u mysql -p err

# Query MySQL server for configured socket path
mysql -e "SHOW VARIABLES LIKE 'socket';" 2>/dev/null || echo "Server not running"

# Check configuration files
grep -r "^socket" /etc/mysql/
grep -r "^socket" ~/.my.cnf

# Common socket locations
# /var/run/mysqld/mysqld.sock - Linux standard
# /var/lib/mysql/mysql.sock - Some distributions
# /tmp/mysql.sock - Fallback location
# /var/run/mysqld/mysqld.sock - Debian/Ubuntu

# Verify client config uses same path
mysql --help | grep socket

# If mismatch exists, update configuration
sudo nano /etc/mysql/my.cnf

# Ensure both server and client sections use same path:
[mysqld]
socket=/var/run/mysqld/mysqld.sock

[client]
socket=/var/run/mysqld/mysqld.sock

# Restart MySQL
sudo systemctl restart mysql

# Check SELinux status (CentOS/RHEL)
getenforce
# Output: Enforcing, Permissive, or Disabled

# View recent SELinux denials
sudo ausearch -m avc -ts recent | grep mysql
sudo grep -i mysql /var/log/audit/audit.log | tail -20

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

# View AppArmor denials
sudo dmesg | grep -i apparmor | grep mysql
sudo journalctl | grep apparmor | grep mysql

# Temporarily disable SELinux to test (TESTING ONLY)
sudo setenforce 0

# Temporarily set MySQL to AppArmor complain mode
sudo aa-complain /usr/sbin/mysqld

# If issue disappears, configure proper policies rather than disabling
# Re-enable SELinux/AppArmor
sudo setenforce 1
sudo aa-enforce /usr/sbin/mysqld