一、更改root密码
1、修改密码

[root@localhost ~]# mysql -uroot -p123456
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 5.6.47 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MySQL [(none)]> set password for root@localhost=password('000000');
Query OK, 0 rows affected (0.00 sec)
MySQL [(none)]> Bye
[root@localhost ~]# mysql -uroot -p000000
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 10
Server version: 5.6.47 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

[root@localhost ~]# mysqladmin  -uroot -p000000 password 123456
[root@localhost ~]# mysql -uroot -p123456
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.6.47 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MySQL [(none)]> 

2、密码重置

[root@localhost ~]# vi /etc/my.cnf    // 编辑配置文件
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
# *** DO NOT EDIT THIS FILE. It's a template which will be copied to the
# *** default location during install, and will be replaced if you
# *** upgrade to a newer version of MySQL.

[mysqld]

# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin

# These are commonly set, remove the # and set as required.
 basedir =/usr/local/mysql
 datadir = /data/mysql
 port = 3306
 server_id = 70
 socket = /var/lib/mysql/mysql.sock

 skip-grant    // 加入这个就可以忽略密码登录
# Remove leading # to set options mainly useful for reporting servers.
@ 
"/etc/my.cnf" 32L, 1165C written
[root@localhost ~]# service mysqld restart    //  配置完文件要重启
Shutting down MySQL.. SUCCESS! 
Starting MySQL.. SUCCESS! 
[root@localhost ~]# mysql    // 不用密码即可登录
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.47 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MySQL [(none)]> 
MySQL [(none)]> 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 [mysql]> update user set password=password('098765') where user='root';  // 重新设置密码
Query OK, 4 rows affected (0.00 sec)
Rows matched: 4  Changed: 4  Warnings: 0

MySQL [mysql]> Ctrl-C -- exit!
Aborted
[root@localhost ~]# vi /etc/my.cnf   // 重新配置文件，删除刚刚加入的那一行
 skip-grant
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/5.6/en/server-configuration-defaults.html
# *** DO NOT EDIT THIS FILE. It's a template which will be copied to the
# *** default location during install, and will be replaced if you
# *** upgrade to a newer version of MySQL.

[mysqld]

# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M

# Remove leading # to turn on a very important data integrity option: logging
# changes to the binary log between backups.
# log_bin

# These are commonly set, remove the # and set as required.
 basedir =/usr/local/mysql
 datadir = /data/mysql
 port = 3306
 server_id = 70
 socket = /var/lib/mysql/mysql.sock

# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
"/etc/my.cnf" 31L, 1153C written
[root@localhost ~]# service mysqld restart
Shutting down MySQL.. SUCCESS! 
Starting MySQL. SUCCESS! 
[root@localhost ~]# mysql -uroot -p098765
Welcome to the MariaDB monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.47 MySQL Community Server (GPL)

Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

MySQL [(none)]>