can't connect to local mysql server through socket '/var/run/mysqld/mysqld.sock' (2) ubuntu 20.04 code example

Example 1: can't connect to local mysql server through socket '/var/run/mysqld/mysqld.sock'

# Start your mysql server
/etc/init.d/mysql start

Example 2: ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.s

> ln -s /var/lib/mysql/mysql.sock /tmp/mysql.sock
> 
> service mysql start or service mysql start

Example 3: Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

service mysql start

Example 4: ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

sudo apt-get install mysql-server