本文記錄了RHEL7.5下mysql 8.0.11安裝教程，具體內容如下
首先去mysql官網下載mysql-8.0.11-el7-x86_64.tar 解壓。
由于mysql初始化、啟動都需要用到mysql用戶，所以創建一個mysql用戶：
useradd -d /home/mysql -m -s /bin/bash mysql
經過測試發現系統中裝有mariadb相關的mysql啟動的時候會報錯，于是卸載和mariadb相關的包。
[root@rhel mysql]# yum remove mariadb*Loaded plugins: axelget, fastestmirror, langpacks, product-id, search-disabled- : repos, subscription-managerThis 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 Resolutionepel/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 MRemoving for dependencies: postfix x86_64 2:2.10.1-6.el7 @base 12 MTransaction Summary================================================================================Remove 1 Package (+1 Dependent package)Installed size: 17 MIs this ok [y/N]: yDownloading packages:Running transaction checkRunning transaction testTransaction test succeededRunning 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 baseNo metadata available for codeNo metadata available for epelNo metadata available for extrasNo metadata available for updatesLoading mirror speeds from cached hostfile * base: mirrors.aliyun.com * epel: mirrors.ustc.edu.cn * extras: mirrors.aliyun.com * updates: mirrors.aliyun.comepel/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數據庫，會在把/var/lib/mysql作為data文件的目錄：
shell> bin/mysqld --initialize --user=mysql
于是我們可以在初始化的時候指定相應的文件目錄：
bin/mysqld --initialize --basedir=/home/mysql --datadir=/home/mysql/data --user=mysql
初始化的時候，會生成一個臨時的密碼，記住該密碼，等登錄到mysql的時候需要用這個密碼，進去后再次修改密碼。
啟動mysql實例：
bin/mysqld --user=mysqlbin/mysqld_safe basedir=/home/mysql --datadir=/home/mysql/data --user=mysql
如果不加 –user=mysql 就會出現如下的提示：
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實例不能正常啟動。
mysql啟動后，使用root用戶登錄，使用剛剛隨機生成的密碼，進去后，通過如下命令修改root用戶的密碼，再做其他操作：
set password ='root';
RHEL7的服務systemctl腳本存放在：/usr/lib/systemd/，有系統（system）和用戶（user）之分，像需要開機不登陸就能運行的程序，還是存在系統服務里吧，即：/usr/lib/systemd/system目錄下
每一個服務以.service結尾，一般會分為3部分：[Unit]、[Service]和[Install]，現在把MYSQL添加進去，具體內容如下：
cat /usr/lib/systemd/system/mysql.service[Unit]Description=mysql ServerAfter=Network.targetAfter=syslog.target[Install]WantedBy=multi-user.target[Service]User=mysqlGroup=mysqlType=forking# Execute pre and post scripts as rootPermissionsStartOnly=true# Start main serviceExecStart=/home/mysql/bin/mysqld --daemonizeExecStop=kill -s -QUIT $MAINPIDRestart=on-failureRestartPreventExitStatus=1PrivateTmp=false
就可以通過systemctl來 啟動，重啟，關閉mysql服務。
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