问题：
困扰了很久的问题
使用apt-get来安装mysql，安装好之后发现安装的是 MariaDB，如下，无需密码既可以登录了。即使使用mysqladmin设置好密码，用密码登录可以，不用密码登录也可以
root@ubuntu:/etc/mysql# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 35
Server version: 10.0.31-MariaDB-0ubuntu0.16.04.2 Ubuntu 16.04
Copyright (c) 2000, 2017, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
排查思路：
第一看看my.conf有没有skip-grant-tables，跳过密码验证
过滤了下没有
看看my.cnf里面是不是把密码写进去了，查找了相关.cnf文件去看了看也没有
root@ubuntu:~# find / -name "*.cnf"
/usr/share/ssl-cert/ssleay.cnf
/usr/share/dovecot/dovecot-openssl.cnf
/usr/lib/ssl/openssl.cnf
/etc/ssl/openssl.cnf
/etc/alternatives/my.cnf
/etc/mysql/my.cnf
/etc/mysql/mariadb.cnf
/etc/mysql/conf.d/mysqldump.cnf
/etc/mysql/conf.d/mysql.cnf
/etc/mysql/mariadb.conf.d/50-mysqld_safe.cnf
/etc/mysql/mariadb.conf.d/50-mysql-clients.cnf
/etc/mysql/mariadb.conf.d/50-client.cnf
/etc/mysql/mariadb.conf.d/50-server.cnf
/etc/mysql/debian.cnf
/var/lib/dpkg/alternatives/my.cnf
root@ubuntu:~#
不过有个小发现：
vim /etc/mysql/debian.cnf
# Automatically generated for Debian scripts. DO NOT TOUCH!
[client]
host = localhost
user = root
password =
socket = /var/run/mysqld/mysqld.sock
[mysql_upgrade]
host = localhost
user = root
password =
socket = /var/run/mysqld/mysqld.sock
basedir = /usr
看了说明是以上由脚本生成，不要改动，
虽然这样写，我也去改了下，加上密码，重启还是不行
最后的最后，去搜索了很久，终于有发现了，是用户插件问题。
第一我去跟安装正常的mysql来比较下，如下
看到这里应该发现问题了，按照正常的修改就行了
sudo service mysql stop
sudo mysqld_safe --skip-grant-tables
进去mysql执行如下命令：
MariaDB [(none)]> UPDATE mysql.user SET authentication_string = PASSWORD('mypassword'), plugin = 'mysql_native_password' WHERE User = 'root' AND Host = 'localhost';
MariaDB [(none)]> FLUSH PRIVILEGES;
验证：
先kill掉mysql kill -9 pid
启动：
sudo service mysql start
最后验证下：需要密码了
root@ubuntu:~# mysql
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)
root@ubuntu:~#