使用mysql登陆数据库报错
[root@localhost ~]# mysql -uroot -p
mysql: unknown variable 'basedir=/usr'

报错原因：
配置文件里面的格式有误，[mysqld]写成了[mysql]
[root@localhost step]# cat /etc/my.cnf
[mysql]
basedir = /usr
datadir = /var/lib/mysql
log-error = /var/lib/mysql/localhost.localdomain.err
pid-file = /var/lib/mysql/localhost.localdomain.pid
log-bin=/var/lib/mysql/mysqld-bin
binlog_format=row
binlog-do-db=dmcdbTEST

解决方法：
将[mysql]改为[mysqld]
[root@localhost step]# cat /etc/my.cnf
[mysqld]
basedir = /usr
datadir = /var/lib/mysql
log-error = /var/lib/mysql/localhost.localdomain.err
pid-file = /var/lib/mysql/localhost.localdomain.pid
log-bin=/var/lib/mysql/mysqld-bin
binlog_format=row
binlog-do-db=dmcdbTEST

之后重启数据库
[root@localhost mysql]# mysqladmin -uroot -p shutdown
[root@localhost mysql]# mysqld_safe --defaults-file=/etc/my.cnf &

数据库可以正常连接
[root@localhost ~]# mysql -uroot -p
Warning: Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.21-70.1 Percona Server (GPL), Release 70.1, Revision 698

Copyright (c) 2009-2014 Percona LLC and/or its affiliates
Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> show global variables like '%double%';
+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| innodb_doublewrite | ON |
+--------------------+-------+
1 row in set (0.00 sec)