今天将Nginx的配置文件 default.conf 重命名为 access_mod.conf 执行重启动命令：
nginx -s reload -c /etc/nginx/nginx.conf
然后报错：Job for nginx.service failed because the control process exited with error code. See "systemctl status nginx.service" and "journalctl -xe" for details.
因为是重命名，没有修改文件内容，配置语法肯定不会出错，按照提示执行：
systemctl status nginx.service
提示：
● nginx.service - nginx - high performance web server
Loaded: loaded (/usr/lib/systemd/system/nginx.service; disabled; vendor preset: disabled)
Active: failed (Result: exit-code) since 日 2020-05-03 22:02:03 CST; 1min 8s ago
Docs: http://nginx.org/en/docs/
Process: 7899 ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf (code=exited, status=1/FAILURE)
5月 03 22:02:03 localhost.localdomain systemd[1]: Starting nginx - high performance web server...
5月 03 22:02:03 localhost.localdomain nginx[7899]: nginx: [emerg] open() "/etc/nginx/conf.d/access_mod.conf" failed (13: Permission denied) in /etc/nginx/nginx.conf:31
5月 03 22:02:03 localhost.localdomain systemd[1]: nginx.service: control process exited, code=exited status=1
5月 03 22:02:03 localhost.localdomain systemd[1]: Failed to start nginx - high performance web server.
5月 03 22:02:03 localhost.localdomain systemd[1]: Unit nginx.service entered failed state.
5月 03 22:02:03 localhost.localdomain systemd[1]: nginx.service failed.
貌似是权限问题，但是查看了一下之前的 default.conf 和 access_mod.conf权限一致啊，经过一番查找，发现一下解决方法：
依次执行：
sudo nginx -c /etc/nginx/nginx.conf
sudo nginx -s reload
启动成功了！奇怪的是以后使用
nginx -s reload -c /etc/nginx/nginx.conf
依然能启动成功。。。我一直用的是root用户，是不是root用户与sudo之间有啥事。。。