1. 默認mysql配置文件在/etc/my.cnf，sudo root賬號找到[mysqld]添加skip-grant-tables（Mac安裝Mysql5.7請戳 http://www.itdecent.cn/p/1fdfba9173f8）

cat /etc/my.cnf
[mysqld]
skip-grant-tables

2. 重啟mysql

(base)  tpt@localhost:/usr/local/etc $ sudo mysql.server restart
Password:
Shutting down MySQL
. SUCCESS!
Starting MySQL
. SUCCESS!

3. 直接登錄mysql(無需輸入賬號密碼)，更改root密碼

(base)  tpt@localhost:/usr/local/etc $ mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.29 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> 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> update user set authentication_string = password('你的密碼'), password_expired = 'N', password_last_changed = now() where user = 'root';
Query OK, 1 row affected, 1 warning (0.03 sec)
Rows matched: 1  Changed: 1  Warnings: 1

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

mysql> quit;
Bye

4. 注釋掉/etc/my.cnf中的skip-grant-tables

vim /etc/my.cnf
[mysqld]
#skip-grant-tables

5. 重啟mysql

(base)  tpt@localhost:/usr/local/etc $ sudo mysql.server restart
Password:
Shutting down MySQL
. SUCCESS!
Starting MySQL
. SUCCESS!

6. 用戶名密碼登錄成功！