Homebrewを使って入れたMySQLが動かない状態に陥った下らない原因 ref: http://qiita.com/takuan_osho/items/961b95373920c3a22aa5

file0.txt

$ mysqld --initialize-insecure --user=taku --basedir=/usr/local/Cellar/mysql/5.7.10 --datadir=/usr/local/var/mysql --tmpdir=/tmp --explicit_defaults_for_timestamp
2016-01-12T11:35:11.104978Z 0 [Warning] Setting lower_case_table_names=2 because file system for /usr/local/var/mysql/ is case insensitive
 100
 100
2016-01-12T11:35:27.326652Z 0 [Warning] InnoDB: New log files created, LSN=45790
2016-01-12T11:35:28.053387Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
2016-01-12T11:35:28.110798Z 0 [ERROR] unknown variable 'innodb_additional_mem_pool_size=16M'
2016-01-12T11:35:28.110818Z 0 [ERROR] Aborting

file1.txt

$ mysql --help | grep my.cnf
                      order of preference, my.cnf, $MYSQL_TCP_PORT,
/etc/my.cnf /etc/mysql/my.cnf /usr/local/etc/my.cnf ~/.my.cnf