centos 安装了Apache，使用 service httpd start 能正常启动Apache，但是页面访问不了，查看Apache错误日志，输出：
[Fri May 17 08:07:12 2019] [notice] Digest: generating secret for digest authentication ...
[Fri May 17 08:07:12 2019] [notice] Digest: done
[Fri May 17 08:07:12 2019] [notice] Apache/2.2.15 (Unix) DAV/2 configured -- resuming normal operations
https://blog.csdn.net/xiaoxianer666/article/details/49175037