Detailed explanation of the solution to forget the password in MySQL 5.7

[root@centos7 ~]# uname -r
3.10.0-514.el7.x86_64
[root@centos7 ~]# cat /etc/redhat-release 
CentOS Linux release 7.3.1611 (Core) 
[root@centos7 ~]# rpm -qa mysql
[root@centos7 ~]# rpm -qa |grep mysql
mysql-community-common-5.7.26-1.el7.x86_64
mysql-community-client-5.7.26-1.el7.x86_64
mysql57-community-release-el7-11.noarch
mysql-community-server-5.7.26-1.el7.x86_64
mysql-community-libs-5.7.26-1.el7.x86_64
mysql-community-libs-compat-5.7.26-1.el7.x86_64

[root@centos7 ~]# mysql -u root -p
Enter password: 
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

grep 'temporary password' /var/log/mysqld.log

[root@centos7 ~]# vim /etc/my.cnf

[mysqld]
     
skip-name-resolve
skip-grant-tables

[root@centos7 ~]# systemctl restart mysqld

[root@centos7 ~]# mysql -u root -p
Enter password: (This is an empty password, just press Enter)
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.7.26 MySQL Community Server (GPL)
 
Copyright (c) 2000, 2019, 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>

mysql> use mysql
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A
 
Database changed
mysql>

mysql> UPDATE user SET authentication_string=PASSWORD('newpassword') where USER='root';
Query OK, 1 row affected, 1 warning (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 1
 
mysql> 
mysql> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)
 
mysql>

[root@centos7 ~]# vim /etc/my.cnf

[mysqld]
     
skip-name-resolve
#skip-grant-tables

[root@centos7 ~]# systemctl restart mysqld

[root@centos7 ~]# mysql -u root -p 
Enter password: (newpassword in previous demonstration)
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.26
 
Copyright (c) 2000, 2019, 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>

ALTER USER testuser IDENTIFIED BY '123456';

ALTER USER USER() IDENTIFIED BY '123456';

mysql> alter user user() identified by 'Linuxpassword!@#';
ERROR 1819 (HY000): Your password does not satisfy the current policy requirements
mysql> alter user user() identified by 'LINUX123password!@#';
Query OK, 0 rows affected (0.00 sec)
 
mysql> 

mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
|mysql |
| performance_schema |
|sys|
+--------------------+
4 rows in set (0.00 sec)
 
mysql> exit
Bye