本文记录了RHEL7.5下mysql 8.0.11安装教程，具体内容如下
首先去mysql官网下载mysql-8.0.11-el7-x86_64.tar 解压。
由于mysql初始化、启动都需要用到mysql用户，所以创建一个mysql用户：
useradd -d /home/mysql -m -s /bin/bash mysql
经过测试发现系统中装有mariadb相关的mysql启动的时候会报错，于是卸载和mariadb相关的包。
[root@rhel mysql]# yum remove mariadb* Loaded plugins: axelget, fastestmirror, langpacks, product-id, search-disabled- : repos, subscription-manager This system is not registered with an entitlement server. You can use subscription-manager to register. Resolving Dependencies --> Running transaction check ---> Package mariadb-libs.x86_64 1:5.5.56-2.el7 will be erased --> Processing Dependency: libmysqlclient.so.18()(64bit) for package: 2:postfix-2.10.1-6.el7.x86_64 --> Processing Dependency: libmysqlclient.so.18(libmysqlclient_18)(64bit) for package: 2:postfix-2.10.1-6.el7.x86_64 --> Running transaction check ---> Package postfix.x86_64 2:2.10.1-6.el7 will be erased --> Finished Dependency Resolution epel/x86_64/group_gz | 266 kB 00:00 Dependencies Resolved ================================================================================ Package Arch Version Repository Size ================================================================================ Removing: mariadb-libs x86_64 1:5.5.56-2.el7 @base 4.4 M Removing for dependencies: postfix x86_64 2:2.10.1-6.el7 @base 12 M Transaction Summary ================================================================================ Remove 1 Package (+1 Dependent package) Installed size: 17 M Is this ok [y/N]: y Downloading packages: Running transaction check Running transaction test Transaction test succeeded Running transaction Erasing : 2:postfix-2.10.1-6.el7.x86_64 1/2 Erasing : 1:mariadb-libs-5.5.56-2.el7.x86_64 2/2 No metadata available for base No metadata available for code No metadata available for epel No metadata available for extras No metadata available for updates Loading mirror speeds from cached hostfile * base: mirrors.aliyun.com * epel: mirrors.ustc.edu.cn * extras: mirrors.aliyun.com * updates: mirrors.aliyun.com epel/x86_64/primary_db | 6.3 MB 00:01 Verifying : 1:mariadb-libs-5.5.56-2.el7.x86_64 1/2 Verifying : 2:postfix-2.10.1-6.el7.x86_64 2/2 Removed: mariadb-libs.x86_64 1:5.5.56-2.el7 Dependency Removed: postfix.x86_64 2:2.10.1-6.el7 Complete!
使用如下命令初始化数据库，会在把/var/lib/mysql作为data文件的目录：
shell> bin/mysqld --initialize --user=mysql
于是我们可以在初始化的时候指定相应的文件目录：
bin/mysqld --initialize --basedir=/home/mysql --datadir=/home/mysql/data --user=mysql
初始化的时候，会生成一个临时的密码，记住该密码，等登录到mysql的时候需要用这个密码，进去后再次修改密码。
启动mysql实例：
bin/mysqld --user=mysql bin/mysqld_safe basedir=/home/mysql --datadir=/home/mysql/data --user=mysql
如果不加 –user=mysql 就会出现如下的提示：
2018-04-22T15:47:25.471462Z 0 [ERROR] [MY-010123] [Server] Fatal error: Please read "Security" section of the manual to find out how to run mysqld as root! 2018-04-22T15:47:25.471514Z 0 [ERROR] [MY-010119] [Server] Aborting
造成mysql实例不能正常启动。
mysql启动后，使用root用户登录，使用刚刚随机生成的密码，进去后，通过如下命令修改root用户的密码，再做其他操作：
set password ='root';
RHEL7的服务systemctl脚本存放在：/usr/lib/systemd/，有系统（system）和用户（user）之分，像需要开机不登陆就能运行的程序，还是存在系统服务里吧，即：/usr/lib/systemd/system目录下
每一个服务以.service结尾，一般会分为3部分：[Unit]、[Service]和[Install]，现在把MYSQL添加进去，具体内容如下：
cat /usr/lib/systemd/system/mysql.service [Unit] Description=mysql Server After=Network.target After=syslog.target [Install] WantedBy=multi-user.target [Service] User=mysql Group=mysql Type=forking # Execute pre and post scripts as root PermissionsStartOnly=true # Start main service ExecStart=/home/mysql/bin/mysqld --daemonize ExecStop=kill -s -QUIT $MAINPID Restart=on-failure RestartPreventExitStatus=1 PrivateTmp=false
就可以通过systemctl来 启动，重启，关闭mysql服务。
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