error_log不生成输出

In a script I have written:

error_log(__FILE__ . ': ' . __LINE__ . "remove trial account at " . date("F j, Y, g:i:s a") . "
",
        3,
        "/var/tmp/recur-billing.log");
    echo "remove trial account at " . date("F j, Y, g:i:s a") . "<br>";

In other words I am sending exactly the same text to both the user invoking the script and the file /var/tmp/recur-billing.log.

When I run the script I see the message displayed to the invoker of the script, but the file /var/tmp/recur-billing.log is not created. I have run this code on two different systems with the same result.

I am trying to debug a complex problem so I have error_log requests to put information into recur-billing.log all through the code. None of those entries were being generated so I assumed the script had failed in some invisible manner. That is why I added the above call to error_log, in a place that I KNEW was executed.

What do I have to do to get php to write the messages?

Other calls to error_log (writing to different file names in /var/tmp) work. It is just the calls trying to write into recur-billing.log that are not working.