[root@tyjs09 ~]# cat /etc/my.cnf
[mysqld]
user=mysql
basedir=/application/mysql
datadir=/data/mysql/data
socket=/tmp/mysql.sock
server_id=6
port=3306
gtid-mode=on
enforce-gtid-consistency=true
log_error=/data/mysql/data/mysql.log
log_bin=/data/binlog/mysql-bin
secure-file-priv=/tmp
innodb_flush_method=O_DIRECT
lower_case_table_names=1
skip-grant-tables

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
mysql> alter user "root"@"localhost" identified by "123456";
ERROR 1396 (HY000): Operation ALTER USER failed for 'root'@'localhost'
mysql> use mysql;select user,host from user;root | % |
| mysql.infoschema | localhost |
| mysql.session | localhost |
| mysql.sys | localhost |
+------------------+-----------+
4 rows in set (0.00 sec)
mysql> ALTER USER 'root'@'%' IDENTIFIED WITH mysql_native_password BY '123456';
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;

[root@tyjs09 ~]# vim /etc/my.cnf
[mysqld]
user=mysql
basedir=/application/mysql
datadir=/data/mysql/data
socket=/tmp/mysql.sock
server_id=6
port=3306
gtid-mode=on
enforce-gtid-consistency=true
log_error=/data/mysql/data/mysql.log
log_bin=/data/binlog/mysql-bin
secure-file-priv=/tmp
innodb_flush_method=O_DIRECT
lower_case_table_names=1
skip-grant-tables #去掉

[root@tyjs09 ~]# service mysql restart
Shutting down MySQL.. SUCCESS!
Starting MySQL. SUCCESS!
[root@tyjs09 ~]# mysql -uroot -p123456
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 8
Server version: 8.0.19 MySQL Community Server - GPL
Copyright (c) 2000, 2020, 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>