How do you stop MySQL on a Mac OS install?

You can always use command "mysqladmin shutdown"

There are different cases depending on whether you installed MySQL with the official binary installer, using MacPorts, or using Homebrew:

Homebrew

brew services start mysql
brew services stop mysql
brew services restart mysql

MacPorts

sudo port load mysql57-server
sudo port unload mysql57-server

Note: this is persistent after a reboot.

Binary installer

sudo /Library/StartupItems/MySQLCOM/MySQLCOM stop
sudo /Library/StartupItems/MySQLCOM/MySQLCOM start
sudo /Library/StartupItems/MySQLCOM/MySQLCOM restart

For those who used homebrew to install MySQL use the following commands below to start, stop, or restart MySQL

Brew start

/usr/local/bin/mysql.server start

Brew restart

/usr/local/bin/mysql.server restart

Brew stop

/usr/local/bin/mysql.server stop