报错（恨恨恨恨恨恨恨！！！！！）：
[root@localhost ~]# sudo yum install mysql-server 已加载插件：fastestmirror, langpacks Determining fastest mirrors Could not retrieve mirrorlist http://mirrorlist.centos.org/?release=7&arch=x86_64&repo=os&infra=stock error was 14: curl#6 - "Could not resolve host: mirrorlist.centos.org; 未知的错误" One of the configured repositories failed (未知), and yum doesn't have enough cached data to continue. At this point the only safe thing yum can do is fail. There are a few ways to work "fix" this: 1. Contact the upstream for the repository and get them to fix the problem. 2. Reconfigure the baseurl/etc. for the repository, to point to a working upstream. This is most often useful if you are using a newer distribution release than is supported by the repository (and the packages for the previous distribution release still work). 3. Run the command with the repository temporarily disabled yum --disablerepo=<repoid> ... 4. Disable the repository permanently, so yum won't use it by default. Yum will then just ignore the repository until you permanently enable it again or use --enablerepo for temporary usage: yum-config-manager --disable <repoid> or subscription-manager repos --disable=<repoid> 5. Configure the failing repository to be skipped, if it is unavailable. Note that yum will try to contact the repo. when it runs most commands, so will have to try and fail each time (and thus. yum will be be much slower). If it is a very temporary problem though, this is often a nice compromise: yum-config-manager --save --setopt=<repoid>.skip_if_unavailable=true Cannot find a valid baseurl for repo: base/7/x86_64
意思是CentOS 7 的官方镜像已经不再可用，导致 yum 无法从标准的仓库中获取软件包信息
解决方法：
首先，卸载掉你那系统自带的数据库
其次
输入 vim /etc/yum.repos.d/CentOS-Base.repo
编辑这该死的文件
把每个部分（这里举例base部分）的mirrorlist注释掉
去掉baseurl的注释 并且将其改成baseurl=http://vault.centos.org/$contentdir/$releasever/os/$basearch/
（！！！！！！！！！！！！！！！！！！！！！！！！！！！很重要！！！！！！！！！！！！！！！！！！！！）
esc退出文件 :wq保存
输入
sudo yum install wget
sudo yum install mysql-server
然后mysql！终于！可以！正常！下载了！！！！！！！！！！！！！！！！
配置篇：
输入：sudo grep 'temporary password' /var/log/mysqld.log
获取随机密码 记住 后面要考
输入：sudo mysql_secure_installation
新密码要求：
- 最少8个字符
- 至少1个大写字母
- 至少1个小写字母
- 至少1个数字
- 至少1个特殊字符
包含图上的虚红色记号 一共五个问题 我是ynnys
令人感动的All done 来之不易
在输入一次 mysql -u root -p登录mysql
登录成功！
