I was having trouble with supervisord being unable to start nginx on a new dev vm I had setup. In the supervisor stderr log for nginx and nginx’s error.log I was getting:
nginx: [warn] the "user" directive makes sense only if the master process runs with super-user privileges, ignored in /opt/nginx-1.9.12/conf/nginx.conf ... nginx: [emerg] bind() to 0.0.0.0:80 failed (13: Permission denied)