[MySQL] 在CentOS8.2上安裝MySQL8.0 與更改root密碼

MySQL 應該是使用 PHP 第一個會碰到的資料庫，通常會包在一起來教學。現在就來教如何在 CentOS8 上來單獨安裝 MySQL 吧!

(環境：CentOS8.2)

1. 在 CentOS8 以後「yum」漸漸的會被「dnf」來取代，因此都會以「dnf」來做套件安裝移除的動作。
2. 開啟 Terminal，安裝 MySQL

   [user@localhost ~]# sudo dnf install -y mysql-server
   ...
   ...
   ...
   ...
   Installed:
     mariadb-connector-c-config-3.0.7-1.el8.noarch                         mecab-0.996-1.module_el8.0.0+41+ca30bab6.9.x86_64                     mysql-8.0.17-3.module_el8.0.0+181+899d6349.x86_64                    
     mysql-common-8.0.17-3.module_el8.0.0+181+899d6349.x86_64              mysql-errmsg-8.0.17-3.module_el8.0.0+181+899d6349.x86_64              mysql-server-8.0.17-3.module_el8.0.0+181+899d6349.x86_64             
     protobuf-lite-3.5.0-7.el8.x86_64                                     
   
   Complete! #看到這行就代表安裝完成囉
   

3. CentOS中的服務安裝好後預設都是不開啟的，所以要手動開啟，看到綠色 running 就代表 MySQL 正在運作囉！

   [user@localhost ~]$ sudo systemctl start mysqld.service   #馬上開啟mysql daeman(MySQL服務)
   
   [user@localhost ~]$ sudo systemctl enable mysqld.service  #之後開機也要自動開啟MySQL服務
   Created symlink /etc/systemd/system/multi-user.target.wants/mysqld.service → /usr/lib/systemd/system/mysqld.service.
   
   [user@localhost ~]$ sudo systemctl status mysqld.service  #查詢MySQL服務的狀態
   ● mysqld.service - MySQL 8.0 database server
      Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
      Active: active (running) since Tue 2020-09-15 12:56:47 CST; 1min 37s ago
    Main PID: 8171 (mysqld)
      Status: "Server is operational"
       Tasks: 38 (limit: 49448)
      Memory: 376.2M
      CGroup: /system.slice/mysqld.service
              └─8171 /usr/libexec/mysqld --basedir=/usr
   
   Sep 15 12:56:46 localhost.localdomain systemd[1]: Starting MySQL 8.0 database server...
   Sep 15 12:56:47 localhost.localdomain systemd[1]: Started MySQL 8.0 database server.
   

4. 可以用「mysql_secure_installation」來設定與安全性相關的設定，這個設定工具可以幫助管理者設定 root 密碼、移除匿名登入帳號、禁止 root 從遠端登入、移除測試用的資料庫。若採用此步驟，可以跳過下一步

   [user@localhost ~]$ sudo mysql_secure_installation
   

5. root 帳號的密碼預設是無，所以登入後一定要改密碼！

   [user@localhost ~]$ mysql -u root   #←不用密碼所以不用參數 -p
   Welcome to the MySQL monitor.  Commands end with ; or \g.
   Your MySQL connection id is 10
   Server version: 8.0.17 Source distribution
   
   Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.
   
   Oracle is a registered trademark of Oracle Corporation and/or its
   affiliates. Other names may be trademarks of their respective
   owners.
   
   Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
   
   mysql>ALTER USER 'root'@'localhost' IDENTIFIED BY 'password';  #password改為要設定的密碼
   Query OK, 0 rows affected (0.00 sec)
   

6. 用密碼登入 MySQL ，看到「Welcome to the MySQL monitor.」就成功囉

   [user@localhost ~]$ mysql -u root -p
   Enter password:        #←這裡輸入剛設定的密碼
   Welcome to the MySQL monitor.  Commands end with ; or \g.
   ...
   ...
   

若是之前有裝過 MySQL，不記得 root 的密碼，請參考(HOW TO REMOVE MYSQL ENTIRELY FROM LINUX SYSTEM(CENTOS))先清除 MySQL 舊的資料再安裝，預設密碼就會為空。