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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：
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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。