mysqlを5.5 -> 5.6にバージョンアップしたら、Can't find file: './mysql/plugin.frm' (errno: 13 - Permission denied)で起動こける

##起動こけるのでエラーログ見ると

cat /usr/local/var/mysql/user.local.err

2015-10-16 14:26:50 13796 [Warning] Setting lower_case_table_names=2 because file system for /usr/local/var/mysql/ is case insensitive
2015-10-16 14:26:50 13796 [Note] Plugin 'FEDERATED' is disabled.
/usr/local/Cellar/mysql/5.6.27/bin/mysqld: Can't find file: './mysql/plugin.frm' (errno: 13 - Permission denied) #←あやしい！！！
2015-10-16 14:26:50 13796 [ERROR] Can't open the mysql.plugin table. Please run mysql_upgrade to create it.
2015-10-16 14:26:50 13796 [Note] InnoDB: Using atomics to ref count buffer pool pages
2015-10-16 14:26:50 13796 [Note] InnoDB: The InnoDB memory heap is disabled
2015-10-16 14:26:50 13796 [Note] InnoDB: Mutexes and rw_locks use GCC atomic builtins
2015-10-16 14:26:50 13796 [Note] InnoDB: Memory barrier is not used
2015-10-16 14:26:50 13796 [Note] InnoDB: Compressed tables use zlib 1.2.3
2015-10-16 14:26:50 13796 [Note] InnoDB: Using CPU crc32 instructions
2015-10-16 14:26:50 13796 [Note] InnoDB: Initializing buffer pool, size = 128.0M
2015-10-16 14:26:50 13796 [Note] InnoDB: Completed initialization of buffer pool
2015-10-16 14:26:50 13796 [ERROR] InnoDB: ./ibdata1 can't be opened in read-write mode
2015-10-16 14:26:50 13796 [ERROR] InnoDB: The system tablespace must be writable!
2015-10-16 14:26:50 13796 [ERROR] Plugin 'InnoDB' init function returned error.
2015-10-16 14:26:50 13796 [ERROR] Plugin 'InnoDB' registration as a STORAGE ENGINE failed.
2015-10-16 14:26:50 13796 [ERROR] Unknown/unsupported storage engine: InnoDB
2015-10-16 14:26:50 13796 [ERROR] Aborting

##権限とオーナーを変える

sudo chown -R _mysql /usr/local/var/mysql
sudo chmod -R g+rwx /usr/local/var/mysql

で解決。

参考
http://stackoverflow.com/questions/21470193/mysql-server-start-issues-on-mavericks