Remember the problem encountered when MySQL 5.7 changes the default password

sudo vim /etc/mysql/mysql.conf.d/mysqld.cnf

Modify the configuration file and add it in [mysqld] skip-grant-tables
After the modification is complete, restart the MySQL service

Then you can log in to the MySQL command line without password

MySQL operation before version 5.7

use mysql;
update user set password=password("new_password") where user="root";
flush privileges;
quit;

MySQL running after version 5.7

use mysql;
update mysql.user set authentication_string=password('new_password') where user='root';
flush privileges;
quit;

I am from version 5.7

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and restarted the MySQL service after performing the above operations, and then logged in and found that an error was reported.

[email protected]:~$ sudo systemctl restart mysql
[email protected]:~$ mysql -uroot -p
Enter password: 
ERROR 1698 (28000): Access denied for user 'root'@'localhost'

The solution is as follows:

sudo vim /etc/mysql/mysql.conf.d/mysqld.cnf

Modify the configuration file and add it in [mysqld] skip-grant-tables
After the modification is complete, restart the MySQL service

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> select user,plugin from user;
+------------------+-----------------------+
| user             | plugin                |
+------------------+-----------------------+
| root             | auth_socket           |
| mysql.session    | mysql_native_password |
| mysql.sys        | mysql_native_password |
| debian-sys-maint | mysql_native_password |
+------------------+-----------------------+
4 rows in set (0.00 sec)

mysql> update user set plugin='mysql_native_password' where user='root';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> select user,plugin from user;
+------------------+-----------------------+
| user             | plugin                |
+------------------+-----------------------+
| root             | mysql_native_password |
| mysql.session    | mysql_native_password |
| mysql.sys        | mysql_native_password |
| debian-sys-maint | mysql_native_password |
+------------------+-----------------------+
4 rows in set (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> quit
Bye

Just restart the MySQL service.