Here’s another post regarding logging…

How to log PHP errors to the same folder than Magento error logs?

It’s quite simple with Nginx and PHP5-FPM. In Nginx virtual host configuration file there is quite likely block like that:

location ~ .php$ {
    if (!-e $request_filename) { rewrite / /index.php last; }
    fastcgi_pass unix:/var/run/php5-fpm.sock;
    fastcgi_param   HTTPS $fastcgi_https;
    fastcgi_param   SCRIPT_FILENAME  $document_root$fastcgi_script_name;
    fastcgi_param   MAGE_RUN_CODE ee;
    fastcgi_param   MAGE_RUN_TYPE website;
    fastcgi_read_timeout    600;
    include /etc/nginx/fastcgi_params;
}

In order to make PHP error logs go to the same folder than Magento’s (/var/log/… add following lines to your virtual host configuration block:

    fastcgi_param   PHP_VALUE "log_errors=on";
    fastcgi_param   PHP_VALUE "display_errors=off";
    fastcgi_param   PHP_VALUE "error_log=$document_root/var/log/php_errors.log";

These are standard PHP directives.
log_errors – this one states that erros must be logged
display_errors – it’s always good to keep it off anywhere else than in your local development machine
error_log – this does the trick. It forces PHP logs for current virtual host to var/log folder under your Magento instance folder.

So the final block should look like this:

location ~ .php$ {
    if (!-e $request_filename) { rewrite / /index.php last; }
    fastcgi_pass unix:/var/run/php5-fpm.sock;
    fastcgi_param   HTTPS $fastcgi_https;
    fastcgi_param   SCRIPT_FILENAME  $document_root$fastcgi_script_name;
    fastcgi_param   MAGE_RUN_CODE ee;
    fastcgi_param   MAGE_RUN_TYPE website;
    fastcgi_read_timeout    600;
    fastcgi_param   PHP_VALUE "log_errors=on";
    fastcgi_param   PHP_VALUE "display_errors=off";
    fastcgi_param   PHP_VALUE "error_log=$document_root/var/log/php_errors.log";
    include /etc/nginx/fastcgi_params;
}

Restart nginx and there you go. You can now tail or less the logs from /var/log/php_errors.log