Question

I must be missing something in my understanding of handling PHP errors, specifically suppressing their output. When a fatal error occurs, I expect my shutdown handler function to process it gracefully and terminate script execution. This works as expected. However, I can’t seem to prevent PHP from outputting the information about the fatal error.

My php.ini file contains the following directives:

error_reporting = E_ALL | E_STRICT
display_errors = Off

I set error_reporting to report everything and I use a custom error handler to throw exceptions. My expectation is that display_errors = Off will prevent ANY error messages from being displayed.

Anyway, when a fatal error occurs the custom error handler is bypassed (because script execution stops immediately) and the shutdown handler executes.

Now, on to my simplified code:

error_reporting(E_ALL | E_STRICT);
ini_set('display_errors', 'Off');

function shutdown_handler()
{
  $err = error_get_last();
  $fatal = array(E_ERROR, E_PARSE, E_CORE_ERROR, E_COMPILE_ERROR);
  if ($err && in_array($err['type'], $fatal)) {
    echo "\n\ntest fatal error output\n\n";
  }
  exit();
}

register_shutdown_function('shutdown_handler');

To test it I generate an “Allowed memory size exhausted” fatal error like so:

// max out available memory
$data = '';
while(true) {
  $data .= str_repeat('#', PHP_INT_MAX);
}

Because i have display_errors = Off I expect this to only produce the following output (as per the shutdown handler):

test fatal error output

But instead I continue to receive:

PHP Fatal error:  Allowed memory size of 134217728 bytes exhausted (tried to allocate 2147483648 bytes) in /home/daniel/mydev/php/test0.php on line 24
PHP Stack trace:
PHP   1. {main}() /home/daniel/mydev/php/test0.php:0
PHP   2. str_repeat() /home/daniel/mydev/php/test0.php:24

test fatal error output

What am I missing that will prevent this error trace from outputting?

---

CONCLUSION

It appears, as @Cthos sagely noted, that “E_ERROR and display_errors don’t play nicely together.”

This is also the case for E_PARSE (and I assume E_CORE_ERROR/E_COMPILE_ERROR, but I didn’t break my PHP installation to test it). I suppose it makes sense that PHP would force the error traceback into STDOUT in these cases because if it didn’t you might never know if/why things were going wrong.

So a solution in this case would be:

1. As @Cthos suggested, silence E_ERROR notifications in php.ini: error_reporting = (E_ALL & ~ E_ERROR) or at runtime using error_reporting(E_ALL & ~ E_ERROR);
2. Update the shutdown handler to check if the last error was of type E_ERROR and perform the appropriate actions if so.

As for the other fatals like E_PARSE, E_CORE_ERROR, etc. you just have to make sure your code is correct and that your PHP works. If you try to silence E_PARSE errors and handle them in your shutdown function it won’t work because parse errors prevent PHP from ever getting that far.

So, an updated/working shutdown handler looks like this:

error_reporting(E_ALL & ~ E_ERROR);

function shutdown_handler()
{
  $err = error_get_last();
  if ($err && $err['type'] == E_ERROR) {
    $msg = 'PHP Fatal Error: '.$err['message'].' in '.$err['file'].
      ' on line '.$err['line'];
    echo $msg, PHP_EOL;
  }
  exit();
}

Answer 1

The unwanted error information is due to the error logging configuration (log_errors and error_log), and is completely independent of the display_errors configuration. The default php.ini configuration logs error details to stderr when running scripts from the command-line. Under Apache, they show up in /etc/httpd/logs/error_log.

Check out the php_error_cb function in main.c of the PHP source. In particular, line 1056 makes it clear that any messages of the format “PHP %s: %s in %s on line %d” are due to the error logging configuration (error information due to display_errors will not have the “PHP: ” prefix).