好奇什么是 soundd 守护进程。http://wiki.centos.org/TipsAndTricks/SelinuxBooleans的 wiki 说它是“soundd 守护进程”，但我在互联网上没有找到太多其他信息。
为了让 nginx（配置为绑定在 unix 套接字上）以 systemctl 启动，我需要在 httpd_t 上向 soundd_port_t:tcp_socket 添加类型强制规则。进一步来说：
sudo systemctl status nginx.service
失败并显示消息：
nginx.service - The nginx HTTP and reverse proxy server
Loaded: loaded (/usr/lib/systemd/system/nginx.service; disabled)
Active: failed (Result: exit-code) since Mon 2015-07-13 19:53:57 EDT; 7s ago
Process: 2699 ExecStartPre=/usr/sbin/nginx -t (code=exited, status=1/FAILURE)
Jul 13 19:53:57 localhost.localdomain nginx[2699]: nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
Jul 13 19:53:57 localhost.localdomain nginx[2699]: nginx: [emerg] bind() to 0.0.0.0:8000 failed (13: Permissi...ied)
Jul …