记在linux下安装mysql填坑过程
前段时间自己租了个云服务，想搭个网站玩儿玩儿，按常规nginx + react + nodejs + mysql的架构。由于一直是做前端开发，没有太多操作linux的经验，在mysql的安装的时候，遇到了很多问题，在网上查询资料，总是没有完整的流程，只能一个问题一个问题的解决，便摘抄记录下贴了出来
参考网上的许多教程，输入如下指令安装mysql
yum install mysql-community-server结果报如下错误（相信大部分同学第一次安装都会遇到同样的错误）：
[root@host ~]# yum install mysql-community-serverLoaded plugins: fastestmirrorSetting up Install ProcessLoading mirror speeds from cached hostfile* base: mirror.san.fastserv.com* elrepo-kernel: repos.lax-noc.com* extras: mirrors.oit.uci.edu* updates: mirror.keystealth.orgResolving Dependencies--> Running transaction check---> Package mysql-community-server.x86_64 0:5.7.20-1.el7 will be installed--> Processing Dependency: mysql-community-common(x86-64) = 5.7.20-1.el7 for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: mysql-community-client(x86-64) >= 5.7.9 for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: systemd for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: systemd for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libstdc++.so.6(GLIBCXX_3.4.15)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libnuma.so.1(libnuma_1.2)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libnuma.so.1(libnuma_1.1)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libc.so.6(GLIBC_2.17)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libsasl2.so.3()(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libnuma.so.1()(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Running transaction check---> Package mysql-community-client.x86_64 0:5.7.20-1.el7 will be installed--> Processing Dependency: mysql-community-libs(x86-64) >= 5.7.9 for package: mysql-community-client-5.7.20-1.el7.x86_64--> Processing Dependency: libstdc++.so.6(GLIBCXX_3.4.15)(64bit) for package: mysql-community-client-5.7.20-1.el7.x86_64--> Processing Dependency: libc.so.6(GLIBC_2.14)(64bit) for package: mysql-community-client-5.7.20-1.el7.x86_64---> Package mysql-community-common.x86_64 0:5.7.20-1.el7 will be installed---> Package mysql-community-server.x86_64 0:5.7.20-1.el7 will be installed--> Processing Dependency: systemd for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: systemd for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libstdc++.so.6(GLIBCXX_3.4.15)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libc.so.6(GLIBC_2.17)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libsasl2.so.3()(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64---> Package numactl.x86_64 0:2.0.9-2.el6 will be installed--> Running transaction check---> Package mysql-community-client.x86_64 0:5.7.20-1.el7 will be installed--> Processing Dependency: libstdc++.so.6(GLIBCXX_3.4.15)(64bit) for package: mysql-community-client-5.7.20-1.el7.x86_64--> Processing Dependency: libc.so.6(GLIBC_2.14)(64bit) for package: mysql-community-client-5.7.20-1.el7.x86_64---> Package mysql-community-libs.x86_64 0:5.7.20-1.el7 will be installed--> Processing Dependency: libc.so.6(GLIBC_2.14)(64bit) for package: mysql-community-libs-5.7.20-1.el7.x86_64---> Package mysql-community-server.x86_64 0:5.7.20-1.el7 will be installed--> Processing Dependency: systemd for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: systemd for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libstdc++.so.6(GLIBCXX_3.4.15)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libc.so.6(GLIBC_2.17)(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Processing Dependency: libsasl2.so.3()(64bit) for package: mysql-community-server-5.7.20-1.el7.x86_64--> Finished Dependency ResolutionError: Package: mysql-community-server-5.7.20-1.el7.x86_64 (mysql57-community)Requires: libsasl2.so.3()(64bit)Error: Package: mysql-community-client-5.7.20-1.el7.x86_64 (mysql57-community)Requires: libstdc++.so.6(GLIBCXX_3.4.15)(64bit)Error: Package: mysql-community-libs-5.7.20-1.el7.x86_64 (mysql57-community)Requires: libc.so.6(GLIBC_2.14)(64bit)Error: Package: mysql-community-server-5.7.20-1.el7.x86_64 (mysql57-community)Requires: systemdError: Package: mysql-community-server-5.7.20-1.el7.x86_64 (mysql57-community)Requires: libstdc++.so.6(GLIBCXX_3.4.15)(64bit)Error: Package: mysql-community-client-5.7.20-1.el7.x86_64 (mysql57-community)Requires: libc.so.6(GLIBC_2.14)(64bit)Error: Package: mysql-community-server-5.7.20-1.el7.x86_64 (mysql57-community)Requires: libc.so.6(GLIBC_2.17)(64bit)You could try using --skip-broken to work around the problemYou could try running: rpm -Va --nofiles --nodigest
度娘查了各种资料和文章，大概确定是mysql的依赖问题。但是中间过程跟着各种教程搞的很乱，又由于对linux的基本目录不够了解，因此搞了很多文件和目录，也不知道该删除哪些。因此打算卸载重装（简单粗暴但有效）这里贴出来卸载mysql重装的方法：
第一步：
删除mysql的思路无非是先使用 yum remove 命令，将之前的安装包移除。但是会有许多残留文件在里面，因此要用命令查找残留的文件，全部删除。
快速删除
yum remove mysql mysql-server mysql-libs查找残留的文件
rpm -qa | grep -i mysql查找残留的目录并删除
whereis mysqlrm -rf 要删除的目录
注意：使用 rm -rf 命令之前，一定要先学习一下命令的使用方式，后面一定要跟上要删除的目标，否则是删除整个当前目录下的所有内容
正式安装：
由于之前已经发现了安装失败的原因，是依赖包没有成功安装导致的，是由于访问国外网站速度慢的问题。因此，这次安装的思路是通过 wget 先将安装包下载到本地，再解压安装包进行安装
mysql的安装分为两部分，一部分是community的交互管理，另一部分是mysql-server服务
先给centOS添加rpm源，并且选择比较新的源（5.7以后的mysql开始收费，所以选择5.7版本安装）
先切到想要下载安装包的目录，个人习惯放在usr下新建目录或者opt目录下新建目录（个人爱好位置，随意）输入如下命令:
wget -i -c http://dev.mysql.com/get/mysql57-community-release-el7-10.noarch.rpm此时输入 ls 命令可以看到当前目录下已经下载了rpm的安装包，输入以下命令进行安装：
yum -y install mysql57-community-release-el7-10.noarch.rpm接着就可以安装mysql服务器了，但是直接安装会出现下载过慢的情况：
yum -y install mysql-community-server安装完成，启动mysql
systemctl start mysqld.service查看mysql的运行状态（当一个服务运行起来之后，systemctl可以监控到它，可以通过systemctl命令进行服务的操作，个人比较习惯使用这个命令进行管理）：
systemctl status mysqld.service看到绿色的active(running)，则表示mysql服务正在运行中，不过要想进入MySQL还得先找出此时root用户的密码，通过如下命令可以在日志文件中找出密码：
grep "password" /var/log/mysqld.log进入数据库命令：
mysql -uroot -p输入初始密码，但如果要操作数据库，必须要先修改密码。根据mysql的要求，密码要比较强的复杂度，与validate_password_policy的值有关，可以通过命令查看密码复杂度要求的规则：
mysql> SHOW VARIABLES LIKE 'validate_password%';+--------------------------------------+-------+| Variable_name | Value |+--------------------------------------+-------+| validate_password_check_user_name | OFF || validate_password_dictionary_file | || validate_password_length | 4 || validate_password_mixed_case_count | 1 || validate_password_number_count | 1 || validate_password_policy | LOW || validate_password_special_char_count | 1 |+--------------------------------------+-------+7 rows in set (0.01 sec)
密码的长度是由validate_password_length决定的，而validate_password_length的计算公式是：
validate_password_length = validate_password_number_count + validate_password_special_char_count + (2 * validate_password_mixed_case_count)
可以通过如下命令对密码复杂度进行修改：
mysql> set global validate_password_policy=0;mysql> set global validate_password_length=1;
此时便可以使用简单的密码进行设置了：
mysql> ALTER USER 'root'@'localhost' IDENTIFIED BY 'new password';但此时还有一个问题，就是因为安装了Yum Repository，以后每次yum操作都会自动更新，需要把这个卸载掉：
yum -y remove mysql57-community-release-el7-10.noarch总算折腾完了。总结起来的主要问题是，对于linux的基本操作和基本工具不够了解，因此后续还要对linux进行比较系统的学习
参考文章：https://segmentfault.com/a/1190000003049498