Failed error_log directive

Hello, I am trying to log all php script errors from a virtualhost to a file. A callback function is not the solution I am looking for. I have tried to the following settings in my httpd.conf (apache) to no avail. php_admin_flag display_errors off php_admin_flag log_errors on php_admin_flag error_log /tmp/phplog When an erroneous file is viewed, errors are not displayed (as expected), however the file /tmp/phplog is not created. I'd be grateful for any help. Thank you.