solution 1：
1.关闭mysql
# service mysqld stop
2.屏蔽权限
# mysqld_safe --skip-grant-tables
3.新开起一个终端输入
# mysql -u root mysql
mysql>update mysql.user set authentication_string=password('123456') where user='root';
mysql> FLUSH PRIVILEGES;//记得要这句话，否则如果关闭先前的终端，又会出现原来的错误
mysql>exit;
solution2：
1.关闭mysql
# service mysqld stop
2.屏蔽权限
# mysqld_safe --skip-grant-tables
3.新开起一个终端输入
# mysql -u root mysql
mysql> delete from user where USER='';
mysql> FLUSH PRIVILEGES;//记得要这句话，否则如果关闭先前的终端，又会出现原来的错误
mysql> exit;
修改密码过程中，遇到如图所示的情况：
查看日志：
解决办法：
sudo service mysql status
sudo service mysql stop
If you have issue stopping then do following
Search for process:
ps aux | grep mysqld
Kill the process:
kill -9 process_id
Now start mysql in safe mode with skip grant
sudo mysqld_safe --skip-grant-tables
排除遇到的问题外，继续执行solution1或者solution2