MySQL 配置
建立MySQL用户及用户组，方便单独管理。因为这个用户不需要直接登录Linux系统，所以无需设置密码。
命令：groupadd mysql
命令：useradd -g mysql mysql
命令：usermod -g mysql mysql #可选
命令：groupadds mysql
查看：mysql -V
CentOS8 运行MySQL失败
启动报错：
[root@localhost singa]# mysql
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2)
[root@localhost singa]# service mysqld start
Redirecting to /bin/systemctl start mysqld.service
Failed to start mysqld.service: Unit mysqld.service not found.
[root@localhost singa]# systemctl start mariadb.service
Failed to start mariadb.service: Unit mariadb.service not found.
问题排查：当出现以上情况时，说明未安装Mariadb.server，在启动MySQL前会强制要求你启动Mariadb.server进行密码等设置
Mariadb.server 使用yum等方式安装失败
[root@localhost singa]# yum install mariadb-server
上次元数据过期检查：0:00:47 前，执行于 2019年11月05日 星期二 15时15分58秒。
错误：
问题: problem with installed package mysql-8.0.17-3.module_el8.0.0+181+899d6349.x86_64
- package mysql-8.0.17-3.module_el8.0.0+181+899d6349.x86_64 conflicts with mariadb provided by mariadb-3:10.3.11-2.module_el8.0.0+35+6f2527ed.x86_64
- package mariadb-3:10.3.11-2.module_el8.0.0+35+6f2527ed.x86_64 conflicts with mysql provided by mysql-8.0.17-3.module_el8.0.0+181+899d6349.x86_64
- package mariadb-server-3:10.3.11-2.module_el8.0.0+35+6f2527ed.x86_64 requires mariadb(x86-64), but none of the providers can be installed
- conflicting requests
- package mysql-8.0.13-1.module_el8.0.0+41+ca30bab6.x86_64 is excluded
(try to add '--allowerasing' to command line to replace conflicting packages or '--skip-broken' to skip uninstallable packages or '--nobest' to use not only best candidate packages)
问题排查：当出现以上情况时，说明使用过
yun install mysql这一命令安装过mysql，或者使用过LNMP等集成环境包，这些安装包没有及时更新mariadb-server服务，所以连接服务失效。mariadb-server服务类似于安装向导，用来配置简单的安全信息，CentOS环境下，MySQL-8.0强制优先配置。
解决办法：CentOS已提供支持
We already supply both mysql and mariadb in the repos.
查看软件包命令：dnf list mysql-server mariadb-server
「尝试在命令行中添加『--allowerasing』以替换有冲突的软件包，或者『skip-broken』以跳过可卸载的软件包，或者『 --nobest』不仅使用最佳候选软件包」
安装命令：yum install mysql-server
安装命令：yum install mariadb-server --allowerasing
在补充完这两个软件包之后，MySQL和Mariadb即刻正常配置。
执行MySQL安全配置向导
命令：systemctl start mariadb.service
命令：systemctl enable mariadb.service
命令：mysql_secure_installation
[root@localhost singa]# mysql_secure_installation
NOTE: RUNNING ALL PARTS OF THIS SCRIPT IS RECOMMENDED FOR ALL MariaDB
SERVERS IN PRODUCTION USE! PLEASE READ EACH STEP CAREFULLY!
In order to log into MariaDB to secure it, we'll need the current
password for the root user. If you've just installed MariaDB, and
you haven't set the root password yet, the password will be blank,
so you should just press enter here.
Enter current password for root (enter for none):
ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: YES)
Enter current password for root (enter for none): #初次运行直接回车
OK, successfully used password, moving on...
Setting the root password ensures that nobody can log into the MariaDB
root user without the proper authorisation.
# 以下全部选Y
Set root password? [Y/n] Y
New password: # 设置root用户密码
Re-enter new password:
Password updated successfully!
Reloading privilege tables..
... Success!
By default, a MariaDB installation has an anonymous user, allowing anyone
to log into MariaDB without having to have a user account created for
them. This is intended only for testing, and to make the installation
go a bit smoother. You should remove them before moving into a
production environment.
Remove anonymous users? [Y/n] Y
... Success!
Normally, root should only be allowed to connect from 'localhost'. This
ensures that someone cannot guess at the root password from the network.
Disallow root login remotely? [Y/n] Y
... Success!
By default, MariaDB comes with a database named 'test' that anyone can
access. This is also intended only for testing, and should be removed
before moving into a production environment.
Remove test database and access to it? [Y/n] Y
- Dropping test database...
... Success!
- Removing privileges on test database...
... Success!
Reloading the privilege tables will ensure that all changes made so far
will take effect immediately.
Reload privilege tables now? [Y/n] Y
... Success!
Cleaning up...
All done! If you've completed all of the above steps, your MariaDB
installation should now be secure.
Thanks for using MariaDB!
启动命令：systemctl start mysql.service
查看启动状态：systemctl status mysqld.service
按q退出
[root@localhost singa]# mysql -V
mysql Ver 15.1 Distrib 10.3.11-MariaDB, for Linux (x86_64) using readline 5.1
我懵了。
啊啊不管了，详细配置信息，请看： Configuring MariaDB with Option Files
