I am running nginx on Raspbian Jessie operating system.

I just created new virtual host and reloaded nginx service:

/etc/init.d/nginx restart

Now I got:

[....] Reloading nginx configuration (via systemctl): nginx.serviceJob for nginx.service failed. See 'systemctl status nginx.service' and 'journalctl -xn' for details.
 failed!

Turns out I can test if the configuration file is OK with:

nginx -t -c /etc/nginx/nginx.conf

This time it says:

nginx: [emerg] could not build the server_names_hash, you should increase server_names_hash_bucket_size: 32
nginx: configuration file /etc/nginx/nginx.conf test failed

Lets check what this setting is in config:

grep server_names_hash_bucket_size /etc/nginx/nginx.conf

And it says that it is not configured:

        # server_names_hash_bucket_size 64;

OK lets increase this as it says:

sed -i "s/^.*server_names_hash_bucket_size..*;$/server_names_hash_bucket_size 64;/" /etc/nginx/nginx.conf

Check again:

grep server_names_hash_bucket_size /etc/nginx/nginx.conf

Its good now:

server_names_hash_bucket_size 64;

Lets test config file:

nginx -t -c /etc/nginx/nginx.conf

This now says:

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

Got to go:

/etc/init.d/nginx restart