环境：CentOS Linux release 7.5.1804 (Core)
MySQL：mysql80-community-release-el7-1
在centos7中默认的是mariadb，先检查系统中是否有MySQL的安装
1.检查：
rpm -qa | grep mysql
[linga@localhost ~]$ sudo rpm -qa | grep mysql
We trust you have received the usual lecture from the local System
Administrator. It usually boils down to these three things:
#1) Respect the privacy of others.
#2) Think before you type.
#3) With great power comes great responsibility.
[sudo] password for linga:
[linga@localhost ~]$
这里返回空值，说明是没有安装
2.先进入本机的源文件目录：
cd /usr/local/src
3.下载MySQL的reop源（这里用的是MySQL8.0版本的，官网介绍说比7.0块2倍）：
weget https://dev.mysql.com/get/mysql80-community-release-el7-1.noarch.rpm
4.安装rpm包：
rpm -ivh mysql80-community-release-el7-1.noarch.rpm
扫描二维码关注公众号，回复： 2931718 查看本文章
5.使用yum源来安装mysql-server：
yum install -y mysql-server
6.启动mysql服务：
systemctl start mysqld
7.设置开机启动MySQL服务：
systemctl enable mysqld
- 修改root本地登录密码：
mysql安装完成之后，在/var/log/mysqld.log文件中给root生成了一个默认密码。通过下面的方式找到root默认密码：
cat /var/log/mysqld.log
2018-08-28T14:51:34.815275Z 0 [System] [MY-013169] [Server] /usr/sbin/mysqld (mysqld 8.0.12) initializing of server in progress as process 1032
2018-08-28T14:51:41.543460Z 5 [Note] [MY-010454] [Server] A temporary password is generated for root@localhost: S0rlNA:RDvu#
2018-08-28T14:51:43.537344Z 0 [System] [MY-013170] [Server] /usr/sbin/mysqld (mysqld 8.0.12) initializing of server has completed
2018-08-28T14:51:46.384749Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.12) starting as process 1332
2018-08-28T14:51:47.708760Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2018-08-28T14:51:48.007536Z 0 [System] [MY-010931] [Server] /usr/sbin/mysqld: ready for connections. Version: '8.0.12' socket: '/var/lib/mysql/mysql.sock' port: 3306 MySQL Community Server - GPL.找到默认密码是：S0rlNA:RDvu#，然后登陆数据库：
mysql -u root -p
输入找到的默认密码，如果要操作数据库时会提示：
mysql> use mysql;
ERROR 1820 (HY000): You must reset your password using ALTER USER statement before executing this statement.提示通过使用ALTER USER 语法来修改密码:
ALTER USER 'root'@'localhost' IDENTIFIED BY 'xxxxxxxxxx';
或者：
set password for 'root'@'localhost'=password('xxxxxxxxxx');
注意：mysql5.7默认安装了密码安全检查插件（validate_password），默认密码检查策略要求密码必须包含：大小写字母、数字和特殊符号，并且长度不能少于8位。否则会提示ERROR 1819 (HY000): Your password does not satisfy the current policy requirements错误
9.通过msyql环境变量可以查看密码策略的相关信息：
show variables like '%password%';
mysql> show variables like '%password%';
+----------------------------------------------+-----------------+
| Variable_name | Value |
+----------------------------------------------+-----------------+
| caching_sha2_password_auto_generate_rsa_keys | ON |
| caching_sha2_password_private_key_path | private_key.pem |
| caching_sha2_password_public_key_path | public_key.pem |
| default_password_lifetime | 0 |
| disconnect_on_expired_password | ON |
| mysql_native_password_proxy_users | OFF |
| password_history | 0 |
| password_reuse_interval | 0 |
| report_password | |
| sha256_password_auto_generate_rsa_keys | ON |
| sha256_password_private_key_path | private_key.pem |
| sha256_password_proxy_users | OFF |
| sha256_password_public_key_path | public_key.pem |
| validate_password.check_user_name | ON |
| validate_password.dictionary_file | |
| validate_password.length | 8 |
| validate_password.mixed_case_count | 1 |
| validate_password.number_count | 1 |
| validate_password.policy | MEDIUM |
| validate_password.special_char_count | 1 |
+----------------------------------------------+-----------------+
20 rows in set (0.01 sec)validate_password_policy：密码策略，默认为MEDIUM策略
validate_password_dictionary_file：密码策略文件，策略为STRONG才需要
validate_password_length：密码最少长度
validate_password_mixed_case_count：大小写字符长度，至少1个
validate_password_number_count ：数字至少1个
validate_password_special_char_count：特殊字符至少1个
上述参数是默认策略MEDIUM的密码检查规则。
共有以下几种密码策略：
| 策略 | 检查规 |
|---|---|
| 0 or LOW Length; | None |
| 1 or MEDIUM Length; | numeric, lowercase/uppercase, and special characters |
| 2 or STRONG Length; | lowercase/uppercase, and special characters; dictionary file |
MySQL官网密码策略详细说明：http://dev.mysql.com/doc/refman/5.7/en/validate-password-options-variables.html#sysvar_validate_password_policy
10.修改密码策略：
在/etc/my.cnf文件添加validate_password_policy配置，指定密码策略
选择0（LOW），1（MEDIUM），2（STRONG）其中一种，选择2需要提供密码字典文件
validate_password_policy=0
如果不需要密码策略，添加my.cnf文件中添加如下配置禁用即可：
validate_password = off
重新启动mysql服务使配置生效：
systemctl restart mysqld
11.添加远程登陆用户：
默认只允许root帐户在本地登录，如果要在其它机器上连接mysql，必须修改root允许远程连接，或者添加一个允许远程连接的帐户，为了安全起见，我添加一个新的帐户：
GRANT ALL PRIVILEGES ON . TO 'yangxin'@'%' IDENTIFIED BY 'Yangxin0917!' WITH GRANT OPTION;
12.配置默认编码为utf8：
修改/etc/my.cnf配置文件，在[mysqld]下添加编码配置，如下所示：
[linga@localhost ~]$ cat /etc/my.cnf
# For advice on how to change settings please see
# http://dev.mysql.com/doc/refman/8.0/en/server-configuration-defaults.html
[mysqld]
#
# Remove leading # and set to the amount of RAM for the most important data
# cache in MySQL. Start at 70% of total RAM for dedicated server, else 10%.
# innodb_buffer_pool_size = 128M
#
# Remove the leading "# " to disable binary logging
# Binary logging captures changes between backups and is enabled by
# default. It's default setting is log_bin=binlog
# disable_log_bin
#
# Remove leading # to set options mainly useful for reporting servers.
# The server defaults are faster for transactions and fast SELECTs.
# Adjust sizes as needed, experiment to find the optimal values.
# join_buffer_size = 128M
# sort_buffer_size = 2M
# read_rnd_buffer_size = 2M
#
# Remove leading # to revert to previous value for default_authentication_plugin,
# this will increase compatibility with older clients. For background, see:
# https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_default_authentication_plugin
# default-authentication-plugin=mysql_native_password
# This is manual addition at 2018/8/28 23:55
character_set_server=utf8
init_connect='SET NAMES utf8'
datadir=/var/lib/mysql
socket=/var/lib/mysql/mysql.sock
log-error=/var/log/mysqld.log
pid-file=/var/run/mysqld/mysqld.pid重启mysql服务：
systemctl restart mysqld
看数据库默认编码:
mysql> show variables like '%character%';
+--------------------------+--------------------------------+
| Variable_name | Value |
+--------------------------+--------------------------------+
| character_set_client | utf8mb4 |
| character_set_connection | utf8mb4 |
| character_set_database | utf8 |
| character_set_filesystem | binary |
| character_set_results | utf8mb4 |
| character_set_server | utf8 |
| character_set_system | utf8 |
| character_sets_dir | /usr/share/mysql-8.0/charsets/ |
+--------------------------+--------------------------------+
8 rows in set (0.01 sec)
默认配置文件路径：
配置文件：/etc/my.cnf
日志文件：/var/log//var/log/mysqld.log
服务启动脚本：/usr/lib/systemd/system/mysqld.service
socket文件：/var/run/mysqld/mysqld.pid