解决 MariaDB无密码就可以登录的问题

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
 Server version: 10.0.-MariaDB-0ubuntu0.16.04. Ubuntu 16.04

 Copyright (c) , , 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

 root@ubuntu:~# cd /etc/mysql/
 root@ubuntu:/etc/mysql# pwd
 /etc/mysql
 root@ubuntu:/etc/mysql# ls -l
 总用量
 drwxr-xr-x  root root  12月   : conf.d
 -rw-------  root root   12月   : debian.cnf
 -rw-------  root root   12月   : debian.cnf-5.7
 -rwxr-xr-x  root root  7月    : debian-start
 -rw-r--r--  root root   7月    : mariadb.cnf
 drwxr-xr-x  root root  12月   : mariadb.conf.d
 lrwxrwxrwx  root root    12月   : my.cnf -> /etc/alternatives/my.cnf
 -rw-r--r--  root root   1月     my.cnf.fallback
 -rw-r--r--  root root   2月      mysql.cnf
 drwxr-xr-x  root root  12月   : mysql.conf.d
 root@ubuntu:/etc/mysql# grep "skip-grant-tables"  -r
 root@ubuntu:/etc/mysql# 

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/-mysqld_safe.cnf
 /etc/mysql/mariadb.conf.d/-mysql-clients.cnf
 /etc/mysql/mariadb.conf.d/-client.cnf
 /etc/mysql/mariadb.conf.d/-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google了很久，终于有发现了,是用户插件问题。

参见这里：https://nixmash.com/post/fix-for-mysql-rootlocalhost-access-denied-on-new-installs

第一我去跟安装正常的mysql来比较下，如下

 正常mysql
 mysql> select user, plugin from mysql.user where plugin = 'mysql_native_password';
 +-----------+-----------------------+
 | user      | plugin                |
 +-----------+-----------------------+
 | root      | mysql_native_password |
 +-----------+-----------------------+
  rows in set (0.00 sec)

 不正常的

 MariaDB [(none)]> select user, plugin from mysql.user;
 +------+-------------+
 | user | plugin      |
 +------+-------------+
 | root | unix_socket |
 +------+-------------+
  row in set (0.00 sec)

看到这里应该发现问题了，按照正常的修改就行了

如下：

 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：
 MariaDB [(none)]> select user, plugin from mysql.user
     -> ;
 +------+-----------------------+
 | user | plugin                |
 +------+-----------------------+
 | root | mysql_native_password |
 +------+-----------------------+
  row in set (0.01 sec)

 先杀死mysql  kill - pid
 启动：
 sudo service mysql start

最后验证下：需要密码了

root@ubuntu:~# mysql
ERROR  (): Access denied for user 'root'@'localhost' (using password: NO)
root@ubuntu:~#