How to change the root password in MySQL 5.7

[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
# The minimum length of the password, default is 8.
validate_password_mixed_case_count
# The minimum number of lowercase or uppercase letters required. The default is 1.
validate_password_number_count
# The minimum number of digits to be included. The default is 1.
validate_password_policy 
# Strength level, can be set to 0, 1, 2.
  【0/LOW】: Only check the length.
  [1/MEDIUM]: Checks numbers, uppercase and lowercase letters, and special characters based on level 0.
  [2/STRONG]: Check the special character dictionary file based on level 1. Here, it is 1.
validate_password_special_char_count
# The minimum number of special characters to be included. The default is 1.