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So I ran into this problem. I was trying to use the ngx_http_realip_module module to forward the correct remote address for an nginx install behind a load balancer.

Using the directive:

    real_ip_header     X-Forwarded-For;

Resulted in nginx: [emerg] unknown directive "set_real_ip_from  " in /etc/nginx/conf.d/

Even though ngx_http_realip_module was installed:

$ nginx -V
nginx version: nginx/1.4.7
built by gcc 4.8.2 20131212 (Red Hat 4.8.2-7) (GCC) 
TLS SNI support enabled
configure arguments: --prefix=/usr/share/nginx --sbin-path=/usr/sbin/nginx --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --http-client-body-temp-path=/var/lib/nginx/tmp/client_body --http-proxy-temp-path=/var/lib/nginx/tmp/proxy --http-fastcgi-temp-path=/var/lib/nginx/tmp/fastcgi --http-uwsgi-temp-path=/var/lib/nginx/tmp/uwsgi --http-scgi-temp-path=/var/lib/nginx/tmp/scgi --pid-path=/var/run/ --lock-path=/var/lock/subsys/nginx --user=nginx --group=nginx --with-file-aio --with-ipv6 --with-http_ssl_module --with-http_spdy_module --with-http_realip_module --with-http_addition_module --with-http_xslt_module --with-http_image_filter_module --with-http_geoip_module --with-http_sub_module --with-http_dav_module --with-http_flv_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_random_index_module --with-http_secure_link_module --with-http_degradation_module --with-http_stub_status_module --with-http_perl_module --with-mail --with-mail_ssl_module --with-pcre --with-google_perftools_module --with-debug --with-cc-opt='-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic' --with-ld-opt=' -Wl,-E'
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Looking at the error message a little closer answered my question. The directive it could not identify was "set_real_ip_from  " not ]"set_real_ip_from"`.

Apparently, white space matters in nginx configuration files. Turns out the configuration (which I must have pasted in from somewhere) had special non-breaking spaces in it. That'll teach me to copy and paste configuration rather than typing it in.

Changing the lines to:

    real_ip_header X-Forwarded-For;

Solved the problem.

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Guess it was some weird space character like non-breakable space. – Alexey Ten Apr 24 '14 at 14:28
That must be it. I've tried adding spaces and tabs since and it still works, the config was copied from the web which must have had that non-breaking space. – Jordan Reiter Apr 24 '14 at 14:30
Don't edit configuration files in Microsoft Office? :) – Michael Hampton Apr 24 '14 at 17:20
I was editing it in the terminal! I copied the config from somewhere; I'm guessing that's where the problem came from. – Jordan Reiter Apr 24 '14 at 19:15

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