MySQL5.7如何修改root密码

[root@centos-linux ~]# cat /var/log/mysqld.log | grep 'password'
2016-07-16T03:07:53.587995Z 1 [Note] A temporary password is generated for root@localhost: 2=s6NZk.t:fz

mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.

mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY '123';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

mysql> show variables like 'vali%';
+--------------------------------------+--------+
| Variable_name            | Value |
+--------------------------------------+--------+
| validate_password_dictionary_file  |    | 
| validate_password_length       | 8   | 
| validate_password_mixed_case_count  | 1   |
| validate_password_number_count    | 1   |
| validate_password_policy       | MEDIUM |
| validate_password_special_char_count | 1   |
+--------------------------------------+--------+
6 rows in set (0.01 sec)

validate_password_length
# 密码的最小长度，默认为8。
validate_password_mixed_case_count
# 至少要包含小写或大写字母的个数，默认为1。
validate_password_number_count
# 至少要包含的数字的个数，默认为1。
validate_password_policy 
# 强度等级，可设置为0、1、2。
  【0/LOW】只检查长度。
  【1/MEDIUM】在0等级的基础上多检查数字、大小写、特殊字符。
  【2/STRONG】在1等级的基础上多检查特殊字符字典文件，此处为1。
validate_password_special_char_count
# 至少要包含的特殊字符的个数，默认为1。