[mysql] Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

After struggling for hours the only thing which worked was

sudo mysql.server start

Then do a secure installation with

mysql_secure_installation 

Then connect to the db via

mysql -uroot -p

Mysql is installed via homebrew and the version is

Server version: 5.7.21 Homebrew

Specifying the version might be helpful as the solution may be different based upon the version.