Arch Linux

Description:

nginx is configured with --error-log-path=/var/log/nginx/error.log. This makes it impossible to log errors to stderr from the configuration file.

from http://nginx.org/en/docs/ngx_core_module.html:
> The first parameter defines a file that will store the log. The special value stderr selects the standard error file.
This means that configuring "error_log stderr" will NOT log to stderr, but to the default error-file, (the compiled-in file).

from http://wiki.nginx.org/InstallOptions:
> After installation, the file name can always be changed in the nginx.conf configuration file using the error_log
> directive. By default the file is named prefix/logs/error.log. The special "stderr" value tells nginx to
> log pre-configuration messages to the standard error.
Aka when using "stderr" as compile-flag, output will be send to stderr as expected

This means that currently (error-log-path=file) it is impossible to log to stderr from the configuration file (you can only specify an alternative file). If however nginx would be compiled with error-log-path=stderr, the configuration could use stderr (to log to stderr) or a file-name.

I have confirmed this by compiling nginx with --error-log-path=stderr