1、查看内置维护账户及密码

hadoop@master:/etc/mysql$ sudo cat /etc/mysql/debian.cnf
# Automatically generated for Debian scripts. DO NOT TOUCH!
[client]
host     = localhost
user     = debian-sys-maint
password = K6Ob75iKnrTAarer
socket   = /var/run/mysqld/mysqld.sock
[mysql_upgrade]
host     = localhost
user     = debian-sys-maint
password = K6Ob75iKnrTAarer
socket   = /var/run/mysqld/mysqld.sock
basedir  = /usr

注：user值为账户名，password值为密码。

2、使用内置维护账户信息登录

hadoop@master:/etc/mysql$ mysql -u debian-sys-maint -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 37
Server version: 5.5.62-0ubuntu0.14.04.1 (Ubuntu)

Copyright (c) 2000, 2018, 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> show databases;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| hive               |
| hue                |
| mysql              |
| performance_schema |
+--------------------+
5 rows in set (0.11 sec)

3. 使用MySQL内置数据库，修改root登录密码

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 mysql.user set authentication_string=password('root') where user='root';
Query OK, 1 row affected, 1 warning (0,00 sec)
Rows matched: 1  Changed: 1  Warnings: 1

mysql> flush privileges;
Query OK, 0 rows affected (0,00 sec)

mysql> exit
Bye

4、重启MySQL数据库服务，使用root密码登录

hadoop@master:/etc/mysql$ sudo /etc/init.d/mysql restart
 * Stopping MySQL database server mysqld                                                                                                                            [ OK ] 
 * Starting MySQL database server mysqld                                                                                                                            [ OK ] 
 * Checking for tables which need an upgrade, are corrupt or were 
not closed cleanly.
hadoop@master:/etc/mysql$ mysql -u root -p            
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 38
Server version: 5.5.62-0ubuntu0.14.04.1 (Ubuntu)

Copyright (c) 2000, 2018, 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>