mysql登陸不了及修改密碼

安裝mariadb，默認是無密碼的，但通常是指要設置密碼的。在設置密碼時出現各類問題，可能仍是不太明白其原理。
一下我嘗試了兩種方法，但都失敗了。下面這兩個是我嘗試的方法：

1、網上最多的方法是
一、輸入下面的指令
mysqladmin -u root -p password newpassword
可是我已輸入提示輸入密碼，我輸入密碼了但提示錯誤，見下
[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)'

二、停掉數據庫服務
systemctl stop mariadb.service
三、對全部的表設置成無密碼登錄。
mysqld_safe --skip-grant-tables &
執行完這條語句提示一下錯誤

[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

四、嘗試退出數據庫，而後重啓服務，再進入
[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

2、正確的操做
一、進到數據庫進行操做
[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

Copyright (c) 2000, 2014, Oracle, MariaDB Corporation Ab and others.

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

二、選擇數據庫
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


修改密碼

UPDATE user SET authentication_string=PASSWORD('aaaAAA111') WHERE user='root';

FLUSH PRIVILEGES;