# vim /etc/my.cnf.d/mysql-server.cnf  #主配置文件[mysqld]下面添加以下內容

[mysqld]
skip-grant-tables  #免密的登陸

#重啟mysql
# systemctl restart mysqld  

mysql> select host,user, authentication_string from mysql.user;
+-----------+------------------+------------------------------------------------------------------------+
| host      | user             | authentication_string                                                  |
+-----------+------------------+------------------------------------------------------------------------+
| localhost | mysql.infoschema | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED |
| localhost | mysql.session    | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED |
| localhost | mysql.sys        | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED |
| localhost | root             | *23AE809DDACAF96AF0FD78ED04B6A265E05AA257                              |
+-----------+------------------+------------------------------------------------------------------------+
4 rows in set (0.00 sec)

# mysql  #進入mysql
mysql> update mysql.user set authentication_string="" where user="root";

+-----------+------------------+------------------------------------------------------------------------+
| host | user | authentication_string |
+-----------+------------------+------------------------------------------------------------------------+
| localhost | mysql.infoschema | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED |
| localhost | mysql.session | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED |
| localhost | mysql.sys | $A$005$THISISACOMBINATIONOFINVALIDSALTANDPASSWORDTHATMUSTNEVERBRBEUSED |
| localhost | root | |
+-----------+------------------+------------------------------------------------------------------------+
4 rows in set (0.00 sec)

mysql>alter user root@"localhost" identified by "123";   #密碼設置為123
mysql> flush privileges;  #使命令生效
mysql> exit;
Bye

# vim /etc/my.cnf.d/mysql-server.cnf  #主配置文件添加以下內容

[mysqld]
#skip-grant-tables  #注釋掉免密的登陸

#重啟mysql
# systemctl restart mysqld  
# mysql -uroot -p123  #使用剛重新設置的密碼登陸mysql

root@mysql20 ~]# mysqladmin  -uroot -p  password "123"
Enter password: //敲回車
mysqladmin: [Warning] Using a password on the command line interface can be insecure.
Warning: Since password will be sent to server in plain text, use ssl connection to ensure password safety.
 [root@mysql20 ~]# mysql //無密碼連接被拒絕
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
[root@mysql20 ~]#
[root@mysql20 ~]# mysql -uroot –ptarena  //連接時輸入密碼