MySQL server startup error 'The server quit without updating PID file'

On [Mac OS X v10.6][1] (Snow Leopard), starting MySQL gives the following error: > The server quit without updating PID file ### File *my.cnf* ### ```lang-none [mysqld] port = 3306 socket = /tmp/mysql.sock skip-external-locking key_buffer_size = 16K pid-file=/var/run/mysqld/mysqld.pid [mysqld_safe] log-error=/var/log/mysqld.log pid-file=/var/run/mysqld/mysqld.pid ``` [1]: https://en.wikipedia.org/wiki/Mac_OS_X_Snow_Leopard