Error

ERROR 2002 (HY000): Can’t connect to local server through socket ‘/run/mysqld/mysqld.sock’ (2)

FIX

sudo apt-get install mysql-server

1. Stop mysql

   sudo /etc/init.d/mysql stop
   

   Or for other distribution versions:

   sudo /etc/init.d/mysqld stop
   

2. Start MySQL in safe mode

   sudo mysqld_safe --skip-grant-tables &
   

3. Log into MySQL using root

   mysql -u root
   

4. Select the MySQL database to use

   use mysql;
   

5. Reset the password
   Explain

   -- MySQL version < 5.7
   update user set password=PASSWORD("mynewpassword") where User='root';
   
   -- MySQL 5.7, mysql.user table "password" field -> "authentication_string"
   
   update user set authentication_string=password('mynewpassword') where user='root';
   

6. Flush the privileges

   flush privileges;
   

7. Restart the server

   quit
   

8. Stop and start the server again

   Ubuntu and Debian:

   sudo /etc/init.d/mysql stop
   ...
   sudo /etc/init.d/mysql start
   

On CentOS, Fedora, and RHEL:

    sudo /etc/init.d/mysqld stop
    ...
    sudo /etc/init.d/mysqld start

9. Login with a new password

   mysql -u root -p
   

10. Type the new password and enjoy your server again like nothing happened

Error

su: warning: cannot change directory to /nonexistent: No such file or directory

Fix

sudo service mysql stop
sudo usermod -d /var/lib/mysql/ mysql
sudo service mysql start