After the upgrade of mysql to version 5.7, the security has increased greatly.

MySQL 5.7 randomly generates a password for root users and prints it in error_log. For the location of error_log, if RPM packages are installed, the default is / var/log/mysqld.log.
So we can find the initial password string in mysqld.log:

cat /var/log/mysqld.log | grep password

Log in with the initial password string:

mysql -u root -p's;*QJ6/gX1et'

But after you log in, you will find that many functions can not be used. Only by changing the password can you operate normally.

So we changed the password:

mysql> SET PASSWORD = PASSWORD('123456'); 
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
mysql> SET PASSWORD = PASSWORD("root");
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements

However, he insisted that the password did not meet the policy requirements.
Let's first look at the current password policy for the database.

mysql root@localhost:(none)> show VARIABLES like "%password%"
+---------------------------------------+---------+
| Variable_name                         | Value   |
|---------------------------------------+---------|
| default_password_lifetime             | 0       |
| disconnect_on_expired_password        | ON      |
| log_builtin_as_identified_by_password | OFF     |
| mysql_native_password_proxy_users     | OFF     |
| old_passwords                         | 0       |
| report_password                       |         |
| sha256_password_proxy_users           | OFF     |
| 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       |
+---------------------------------------+---------+

According to the official documents, we can find that the policy is 1, MEDIUM.

ALTER USER 'root'@'localhost' IDENTIFIED BY 'new_password';
//perhaps
SET password='new_password';

So you can successfully change the password, and finally you have to set the expiration time to prevent password invalidation.
Add in / etc/my.cnf configuration file

[mysqld]
default_password_lifetime=0

Or set it directly by command

ALTER USER 'script'@'localhost' PASSWORD EXPIRE NEVER

Above all, you can roam in the world of mysql happily.

Foreign article

But sometimes in order to facilitate the graph, the data security requirements are not very high, we usually prefer to set a simple password, such as 123456.

Law 1:

Add in / etc/my.cnf configuration file

[mysqld]
validate_password=off

Then service mysqld restart or system CTL restart mysqld. service restart mysqld, through SHOW PLUGINS; you can see that the password validation plug-in has been stopped.

+-------------------+----------+-------------------+----------------------+-----+
| validate_password | DISABLED | VALIDATE PASSWORD | validate_password.so | GPL |
+-------------------+----------+-------------------+----------------------+-----+

Law two:

set global validate_password_policy=0;

set global validate_password_length=0;

In this way, the password can be set at will:

update mysql.user set authentication_string=password('123456') where user='root' and Host = 'localhost';
//perhaps
set password for 'root'@'localhost'=password('123456');

Of course, there is another way that we do not set the initial password at the very beginning:

Simply specify -- initialize-insecure at initialization time, such as:

mysqld --initialize-insecure --datadir=/var/lib/mysql --basedir=/usr --user=mysql

At this point, SHOW VARIABLES LIKE'vali%'; will also be empty because the plug-in is not installed.