How to fix ERROR 2002: Can't connect to MySQL server in MySQL

# Check MySQL service status
sudo systemctl status mysql
# or
sudo systemctl status mysqld
# or
sudo service mysql status

# Check if MySQL process exists
ps aux | grep mysqld
sudo pgrep -a mysqld

# Check for socket file existence
ls -la /var/run/mysqld/mysqld.sock
ls -la /tmp/mysql.sock
ls -la /var/lib/mysql/mysql.sock

# Start MySQL if not running
sudo systemctl start mysql
# or
sudo service mysql start

# Check MySQL error logs for startup issues
sudo tail -50 /var/log/mysql/error.log
sudo journalctl -u mysql -n 50

# Find where socket file actually is
sudo find / -name mysqld.sock 2>/dev/null
sudo find /var /tmp -name "mysql.sock*" 2>/dev/null

# Check socket file details
ls -la /var/run/mysqld/mysqld.sock
stat /var/run/mysqld/mysqld.sock

# Check directory permissions
ls -la /var/run/mysqld/
ls -la /var/lib/mysql/

# Expected permissions:
# Socket file: srwxrwxrwx (777) or similar
# Owner: mysql:mysql
# Directory: drwxr-x--- or drwxr-xr-x

# If permissions are wrong, fix them
sudo chmod 755 /var/run/mysqld
sudo chown mysql:mysql /var/run/mysqld/mysqld.sock

# Ensure mysql user can access directory
sudo chown mysql:mysql /var/run/mysqld
sudo chmod 755 /var/run/mysqld

# Check what socket path the running MySQL uses
sudo mysql -e "SELECT @@socket;" 2>/dev/null || echo "Server not running"

# Check server configuration file
sudo cat /etc/mysql/mysql.cnf
sudo cat /etc/mysql/mysql.conf.d/mysqld.cnf
sudo cat /etc/mysql/conf.d/*.cnf
sudo cat /etc/my.cnf

# Look for socket configuration lines:
# [mysqld]
# socket=/var/run/mysqld/mysqld.sock

# Check client configuration
sudo cat /etc/mysql/mysql.conf.d/mysql.cnf

# Look for client socket settings:
# [mysql]
# socket=/var/run/mysqld/mysqld.sock

# If socket paths don't match, edit config files to align them
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

# Both should specify same socket path:
[mysqld]
socket=/var/run/mysqld/mysqld.sock

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

# Restart MySQL to apply changes
sudo systemctl restart mysql

# Connect via TCP/IP (127.0.0.1) instead of socket (localhost)
mysql -h 127.0.0.1 -P 3306 -u root -p

# Specify the socket path explicitly
mysql -u root -p --socket=/var/run/mysqld/mysqld.sock

# Try alternate socket locations
mysql -u root -p --socket=/tmp/mysql.sock
mysql -u root -p --socket=/var/lib/mysql/mysql.sock

# Stop MySQL completely
sudo systemctl stop mysql
# or
sudo service mysql stop

# Verify process is stopped
ps aux | grep mysqld  # Should show no mysqld processes

# Check socket file is removed
ls -la /var/run/mysqld/mysqld.sock 2>/dev/null || echo "Socket removed (expected)"

# Start MySQL fresh
sudo systemctl start mysql

# Verify socket file is recreated
sleep 2  # Wait for socket to be created
ls -la /var/run/mysqld/mysqld.sock

# Test connection
mysql -u root -p

# If still fails, check logs immediately
sudo tail -20 /var/log/mysql/error.log

# Check disk usage
df -h /var
df -h /tmp
df -h /var/run
df -h /var/lib/mysql

# Check available inodes
df -i /var
df -i /tmp
df -i /var/run

# If disk is full (0% available), free up space
du -sh /var/log/*
du -sh /var/cache/*
du -sh /tmp/*

# Clear old log files
sudo rm /var/log/mysql/*.gz  # Remove compressed archives
sudo find /var/log -name "*.log.*" -delete  # Old rotated logs

# Clear temp files
sudo rm -rf /tmp/*

# Clear package cache
sudo apt-get clean  # Debian/Ubuntu
sudo yum clean all  # CentOS/RHEL

# After freeing space, restart MySQL
sudo systemctl restart mysql

# Verify socket is created
ls -la /var/run/mysqld/mysqld.sock

# Stop MySQL
sudo systemctl stop mysql

# Remove MySQL package (keep configuration/data backup first)
sudo mysqldump -u root -p --all-databases > ~/mysql_backup.sql

# Uninstall MySQL completely
sudo apt-get remove mysql-server mysql-client mysql-common  # Debian/Ubuntu
sudo yum remove mysql-server mysql-client  # CentOS/RHEL

# Remove data and configuration
sudo rm -rf /var/lib/mysql
sudo rm -rf /var/log/mysql
sudo rm -rf /etc/mysql
sudo userdel mysql

# Reinstall MySQL
sudo apt-get install mysql-server  # Debian/Ubuntu
sudo yum install mysql-server  # CentOS/RHEL

# Start fresh installation
sudo systemctl start mysql

# Run security script (recommended)
sudo mysql_secure_installation

# Restore data if needed
mysql -u root -p < ~/mysql_backup.sql

# Verify connection works
mysql -u root -p