This is for software built from source according to:
http://hivelogic.com/articles/installing-mysql-on-mac-os-x/

Start MySQL

sudo launchctl unload -w /Library/LaunchDaemons/com.mysql.mysqld.plist

Stop MySQL

sudo launchctl load -w /Library/LaunchDaemons/com.mysql.mysqld.plist

You have to symlink mysql to the location on osx

first find out where mysql has put the socket:

mysql_config5 --socket

Next symlink /tmp/mysql.sock to the right location of the socket

sudo ln -s path-of-mysql.sock-from-above /tmp/mysql.sock

Start MySQL

sudo /opt/local/share/mysql5/mysql/mysql.server start

or

/opt/local/bin/mysqld_safe5

Stop MySQL

sudo /opt/local/share/mysql5/mysql/mysql.server stop

#starting SQL:

sudo /usr/local/mysql/support-files/mysql.server start

Stoping SQL:

sudo /usr/local/mysql/support-files/mysql.server stop

Running the Standalone Server
-----------------------------
After having created a Trac environment, you can easily try the web interface
by running the standalone server tracd:

  $ tracd --port 8000 /path/to/projectenv

Then, fire up a browser and visit http://localhost:8000/. You should get a
simple listing of all environments that tracd knows about. Follow the link
to the environment you just created, and you should see Trac in action.