之前在小型机上装了feroda系统，装了mysql后，发现无法找到root用户密码，
mysqld_safe也不能用，最后发现一片文章，原来mysql5.7可以通过my.cnf配置文件设置不验证密码。记录下全文。
1、mysql安装检查：yum list installed | grep mysql
如果已经有的话执行命令yum -y remove mysql-libs.x86_64卸载已经安装的mysql。
2、先到mysql官网http://dev.mysql.com/downloads/mysql/下载5.7的安装包，download-yum选择Red Hat Enterprise Linux 7 / Oracle Linux 7 (ArchitectureIndependent), RPM Package ，
进入系统下载安装包：
wget http://repo.mysql.com//mysql57-community-release-el7-7.noarch.rpm
如果新的系统还没有wget命令的话可以先：
yum install wget
3、添加选择yum源：
yum localinstall mysql57-community-release-el7-7.noarch.rpm
yum repolist all | grep mysql
4、安装mysql：
yum install mysql-community-server
5、安装完成之后会自动在log中生成连接的密码，
启动mysql：
#service mysqld start
查看密码：
#cat /var/log/mysqld.log |grep password
>2016-08-23T02:33:48.872073Z 1 [Note] A temporary password isgenerated for root@localhost: %IrczkB+J7Ez
你必须重新设置密码才能执行语句
[root@mysqlA ~]# mysql -uroot -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 4
Server version: 5.7.14
Copyright (c) 2000, 2016, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.
>ALTER USER USER() IDENTIFIED BY '需要设置安全等级很高的密码，否则报错';
#或者如下：
>ALTER USER 'root'@'localhost' identified by '需要设置安全等级很高的密码，否则报错' password expire never;
#这个错误是因为密码太简单
RROR 1819 (HY000): Your password does not satisfy the current policy requirements
6、重置 5.7 的密码很简单：
1) 修改/etc/my.cnf，在 [mysqld] 小节下添加一行：skip-grant-tables=1
这一行配置让 mysqld 启动时不对密码进行验证
2) 重启mysqld 服务：`service mysqld restart`
3) 使用 root 用户登录到 mysql：`mysql -u root `
4) 切换到mysql数据库，更新 user 表：
update user set authentication_string = password('123456'),password_expired = 'N', password_last_changed = now() where user = 'root'; 在之前的版本中，密码字段的字段名是 password，5.7版本改为了 authentication_string
5) 退出 mysql，编辑 `/etc/my.cnf` 文件，删除 `skip-grant-tables=1`的内容
7、重启mysqld 服务，再用新密码登录即可
[root@mysqlA ~]# mysql -V
mysql Ver 14.14 Distrib5.7.14, for Linux (x86_64) using EditLine wrapper
8、允许远程连接
mysql> select user,host from mysql.user;
+-----------+-----------+
| user | host |
+-----------+-----------+
| mysql.sys | localhost |
| root | localhost |
+-----------+-----------+
2 rows in set (0.00 sec)
mysql>grant all privileges on *.* to 'root'@'%' identified by 'password' with grant option;
9、修改密码多种方法
方法1： 用SET PASSWORD命令
mysql -u root
mysql> SET PASSWORD FOR 'root'@'localhost' = PASSWORD('newpass');
方法2：用mysqladmin
mysqladmin -u root password "newpass"
#如果root已经设置过密码，采用如下方法
mysqladmin -u root password oldpass "newpass"
方法3： 用UPDATE直接编辑user表
mysql -u root
mysql> use mysql;
mysql> UPDATE user SET Password = PASSWORD('newpass') WHERE user = 'root';
mysql> FLUSH PRIVILEGES;
在丢失root密码的时候，可以这样
mysqld_safe --skip-grant-tables&
mysql -u root mysql
mysql> UPDATE user SET password=PASSWORD("new password") WHERE user='root';
mysql> FLUSH PRIVILEGES;
方法4: 使用ALTER USER修改用户信息
ALTER USER 'root'@'localhost'
IDENTIFIED BY 'new_password' PASSWORD EXPIRE NEVER;
