环境为centos7.7 + mysql 8.0.18
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示例：
1、编辑配置文件my.cnf
vi /etc/my.cnf
增加内容：port=6612
2、重启mysql服务
# systemctl start mysqld.service
显示错误如下：
Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details.
3、查看日志
# tail -200f /var/log/mysqld.log
日志显示如下错误：
2020-07-23T08:00:36.544775Z 0 [Warning] [MY-010139] [Server] Changed limits: max_open_files: 10000 (requested 10010)
2020-07-23T08:00:36.544787Z 0 [Warning] [MY-010142] [Server] Changed limits: table_open_cache: 3995 (requested 4000)
2020-07-23T08:00:36.822452Z 0 [System] [MY-010116] [Server] /usr/sbin/mysqld (mysqld 8.0.18) starting as process 21372
2020-07-23T08:00:37.784812Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2020-07-23T08:00:37.786871Z 0 [ERROR] [MY-010262] [Server] Can't start server: Bind on TCP/IP port: Permission denied
2020-07-23T08:00:37.787184Z 0 [ERROR] [MY-010257] [Server] Do you already have another mysqld server running on port: 6612 ?
2020-07-23T08:00:37.787506Z 0 [ERROR] [MY-010119] [Server] Aborting
2020-07-23T08:00:38.998982Z 0 [System] [MY-010910] [Server] /usr/sbin/mysqld: Shutdown complete (mysqld 8.0.18) MySQL Community Server - GPL.
4、原因：selinux防火墙未关闭
解决方案：
vi /etc/selinux/config
SELINUX=disabled
#立即关闭
setenforce 0