centos7 设置mariadb密码

安装mariadb，默认是无密码的，但一般是指要设置密码的。在设置密码时出现各种问题，可能还是不太明白其原理。
一下我尝试了两种方法，但都失败了。下面这两个是我尝试的方法：

一、网上最多的方法是

1、输入下面的指令

mysqladmin -u root -p password newpassword

但是我已输入提示输入密码，我输入密码了但提示错误，见下
[root@localhost sakila]# mysqladmin -u root -p password newpasswd
Enter password:
mysqladmin: connect to server at 'localhost' failed
error: 'Access denied for user 'root'@'localhost' (using password: YES)'

2、停掉数据库服务

systemctl stop mariadb.service

3、对所有的表设置成无密码登陆。

mysqld_safe --skip-grant-tables &

执行完这条语句提示一下错误

[root@localhost sakila]# mysqld_safe --skip-grant-tables &
[1] 14275
[root@localhost sakila]# 150424 10:13:41 mysqld_safe Logging to '/var/log/mariadb/mariadb.l
og'.150424 10:13:41 mysqld_safe Starting mysqld daemon with databases from /var/lib/mysql

4、尝试退出数据库，然后重启服务，再进入

[root@localhost sakila]# systemctl restart mariadb.service
[root@localhost sakila]# mysqladmin -u root -p password 'passwd'
Enter password:
mysqladmin:
You cannot use 'password' command as mysqld runs
with grant tables disabled (was started with --skip-grant-tables).
Use: "mysqladmin flush-privileges password '*'" instead

二、正确的操作

1、进到数据库进行操作

[root@localhost etc]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 7
Server version: 5.5.41-MariaDB MariaDB Server

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

MariaDB [(none)]> mysql
-> ;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds
to your MariaDB server version for the right syntax to use near 'mysql' at line 1MariaDB [(none)]> update user set password=password("123456")where user='root';
ERROR 1046 (3D000): No database selected

2、选择数据库

MariaDB [(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

3、用户root添加密码

MariaDB [mysql]> update user set password=password("123456")where user='root';
Query OK, 0 rows affected (0.00 sec)
Rows matched: 4 Changed: 0 Warnings: 0

4、赋予权限

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

5、退出，重新登录

MariaDB [mysql]> exit
Bye

6、尝试无密码是否可以登录

[root@localhost etc]# mysql

提示错误

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

7、输入密码登陆

[root@localhost etc]# mysql -u root -p123456
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 9
Server version: 5.5.41-MariaDB MariaDB Server