通过Brew安装的MySQL从8.2降级到8.0.35后无法启动

操作过程 #

• 执行brew install mysql安装8.2版本，因与Workbench不兼容，执行brew uninstall mysql卸载
• 安装8.0系列最新版本：brew install mysql@8.0
• 重启服务：brew services restart mysql@8.0
• 执行初始化命令mysql_secure_installation，输入密码后报错：

  Error: Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)

已尝试的无效方案 #

• 在my.cnf中配置127.0.0.1——已设置但无效
• 在my.cnf添加socket=/var/lib/mysql/mysql.sock——重启后无效
• 使用mysql -h 127.0.0.1 -P 3306 -u root -p连接——失败

关键错误日志 #

运行mysqld后输出核心错误：

2023-12-14T23:37:41.322399Z 0 [System] [MY-010116] [Server] /opt/homebrew/Cellar/mysql@8.0/8.0.35/bin/mysqld (mysqld 8.0.35) starting as process 13478
2023-12-14T23:37:41.324735Z 0 [Warning] [MY-010159] [Server] Setting lower_case_table_names=2 because file system for /opt/homebrew/var/mysql/ is case insensitive
2023-12-14T23:37:41.329772Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2023-12-14T23:38:00.170514Z 1 [ERROR] [MY-014061] [InnoDB] Invalid MySQL server downgrade: Cannot downgrade from 80200 to 80035. Downgrade is only permitted between patch releases.
mysqld: Can't open file: 'mysql.ibd' (errno: 0 - )
2023-12-14T23:38:00.226999Z 1 [ERROR] [MY-010334] [Server] Failed to initialize DD Storage Engine
2023-12-14T23:38:00.227083Z 0 [ERROR] [MY-010020] [Server] Data Dictionary initialization failed.
2023-12-14T23:38:00.227093Z 0 [ERROR] [MY-010119] [Server] Aborting
2023-12-14T23:38:00.228201Z 0 [System] [MY-010910] [Server] /opt/homebrew/Cellar/mysql@8.0/8.0.35/bin/mysqld: Shutdown complete (mysqld 8.0.35)  Homebrew.

解决办法 #

问题根源是卸载8.2版本时未清理旧数据目录，8.2的InnoDB数据文件无法被8.0版本兼容读取，需彻底清理后重新初始化：

1. 停止所有MySQL服务：

   brew services stop mysql@8.0
   

2. 备份旧数据目录（可选，需保留旧数据时执行）：

   sudo mv /opt/homebrew/var/mysql /opt/homebrew/var/mysql_backup
   

   若无需保留旧数据，直接删除：

   sudo rm -rf /opt/homebrew/var/mysql
   

3. 重新初始化MySQL：

   mysqld --initialize --user=_mysql --basedir=/opt/homebrew/Cellar/mysql@8.0/8.0.35 --datadir=/opt/homebrew/var/mysql
   

4. 启动MySQL服务：

   brew services start mysql@8.0
   

5. 查看临时初始密码（用于后续安全初始化）：

   grep 'temporary password' /opt/homebrew/var/mysql/*.err
   

6. 执行安全初始化命令，输入临时密码后设置新密码并完成配置：

   mysql_secure_installation
   

内容的提问来源于stack exchange，提问作者Jossy