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?

Just a note: is the parent directory readable?

Aleks G
– Aleks G

2011-08-19 11:20:58 +00:00
Commented Aug 19, 2011 at 11:20 — Aleks G
– Aleks G, Commented Aug 19, 2011 at 11:20

phihag · Accepted Answer · 2011-08-19 13:35:43Z

11

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);

edited Aug 19, 2011 at 13:35

answered Aug 19, 2011 at 11:24

phihag

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10 Comments

lbednaszynski Over a year ago

I understand that file can disappear between two calls, but I am only one who tests this application. I also test it only for one user thats why it is strange for me. I can ignore error by putting @ sign, but the problem will not disappear.

Maxim Krizhanovsky Over a year ago

I don't like solutions that include error suppression, but +1 for the effective/real note. @marchewa check the permissions of the files.

lbednaszynski Over a year ago

Permissions of all cached files are 0644 (rw-r--r--). My scripts create, deletes and try to read these files. As I said only about 10% of requests fail.

phihag Over a year ago

@Darhazer What's wrong with error suppression if errors are expected? It's definitely better than look-before-you-leap unless you can guarantee the state won't change.

phihag Over a year ago

@marchewa If the problem only occurs intermittently, it could very well be that the temporary file is removed after you call file_exists, but before filemtime. Can you reproduce the problem with two calls to filemtime, i.e. using (@filemtime(..) !== false) instead of file_exists?

|

kbec · Accepted Answer · 2012-05-16 11:53:46Z

2

Use:

Smarty::muteExpectedErrors();

Read this and this

answered May 16, 2012 at 11:53

kbec

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Comments

Jeff · Accepted Answer · 2011-09-05 19:08:24Z

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.

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