PHP filemtime function - “stat failed for”

Question

I have a problem with PHP filemtime function. In my webapp I use Smarty template engine with caching option. In my webapp I can do some actions which generate error, but lets focus on only one action. When I click link on page some content is updated - I can click few times and everything is OK but about one request on 10 fails. Following error occurs:

filemtime() [<a href='function.filemtime'>function.filemtime</a>]: stat failed for

and the line that causes the problem:

 return ($_template->getCachedFilepath() && file_exists($_template->getCachedFilepath())) ? filemtime($_template->getCachedFilepath()) : false ;

As you can see, file exists because it is checked.

Problematic line of code is included in smarty_internal_cacheresource_file.php (part of Smarty lib v3.0.6)

App is run on UNIX system, external hosting.

Any ideas? Should I post more details?

Answer 1

file_exists internally uses the access system call which checks permissions as the real user, whereas filemtime uses stat, which performs the check as the effective user. Therefore, the problem may be rooted in the assumption of effective user == real user, which does not hold. Another explanation would be that the file gets deleted between the two calls.

Since both the result of $_template->getCachedFilepath() and the existance of the file can change in between system calls, why do you call file_exists at all? Instead, I'd suggest just

return @filemtime($_template->getCachedFilepath());

If $_template->getCachedFilepath() can be set to a dummy value such as false, use the following:

$path = $_template->getCachedFilepath();
if (!$path) return false;
return @filemtime($path);

Answer 2

Use:

Smarty::muteExpectedErrors();

Read this and this

Answer 3

I used filemtime successfully without checking "file_exists" for years. The way I have always interpreted the documentation is that FALSE should be returned from "filemtime" upon any error. Then a few days ago something very weird occurred. If the file did not exist, my Cron job terminated with a result. The result was not in the program output but rather in the Cron output. The message was "file length exceeded". I knew the Cron job ended on the filemtime statement because I sent myself an email before and after that statement. The "after" email never arrived.

I inserted a file_exists check on the file to fix the Cron job. However, that should not have been necessary. I still do not know what was changed on the hosting server I use. Several other Cron jobs started failing on the same day. I do not know yet whether they have anything to do with filemtime.