Locate the nginx.conf file my nginx is actually using

Running nginx -t through your commandline will issue out a test and append the output with the filepath to the configuration file (with either an error or success message).

Both nginx -t and nginx -V would print out the default nginx config file path.

$ nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

$ nginx -V
nginx version: nginx/1.11.1
built by gcc 4.9.2 (Debian 4.9.2-10)
built with OpenSSL 1.0.1k 8 Jan 2015
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/modules --conf-path=/etc/nginx/nginx.conf ...

If you want, you can get the config file by:

$ nginx -V 2>&1 | grep -o '\-\-conf-path=\(.*conf\)' | cut -d '=' -f2
/etc/nginx/nginx.conf

Even if you have loaded some other config file, they would still print out the default value.

---

ps aux would show you the current loaded nginx config file.

$ ps aux
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root        11  0.0  0.2  31720  2212 ?        Ss   Jul23   0:00 nginx: master process nginx -c /app/nginx.conf

So that you could actually get the config file by for example:

$ ps aux | grep "[c]onf" | awk '{print $(NF)}'
/app/nginx.conf