Moodle in English: Help required! Getting Error:Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write.

Hi All

I am in a bit of a spot here - I have a virtual machine that I backed up which is running my production instance of moodle at version 2.5.2.

When I restored the Virtual Machine to a new volume, and launch my moodle, I get the following error when attempting to access the site:

"Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write."

I could use some serious assistance in diagnosing this error. I cannot get the site to launch, and need to get the site up and running as soon as possible. I cannot see what I did wrong - I have done this a number times and have never encountered anything so bizarre

Mike

As best as I can tell, the error relates to the following code referenced in /var/www/moodle/cache/stores/file/lib.php - as per the file:

/**
     * Prepares the data it has been read from the cache. Undoing what was done in prep_data_before_save.
     *
     * @param string $data
     * @return mixed
     * @throws coding_exception
     */
    protected function prep_data_after_read($data) {
        $result = @unserialize($data);
        if ($result === false) {
            throw new coding_exception('Failed to unserialise data from file. Either failed to read, or failed to write.');
        }
        return $result;
    }

I would presume that there is a cache file associated with this code that has become corrupt. If anyone has any insight as to how I may clear it, if I am on the right track, I would be grateful.

Mike

Resolved.

So, I figured out that the code is locking the file handle on the resulting cache file that is being created, but the developers kindly indicated that they don't care if gets locked, as per statement below:

// Lock it up!
        // We don't care if this succeeds or not, on some systems it will, on some it won't, meah either way.
        flock($handle, LOCK_SH);
        $data = '';
        // Read the data in 1Mb chunks. Small caches will not loop more than once. We don't use filesize as it may
        // be cached with a different value than what we need to read from the file.
        do {
            $data .= fread($handle, 1048576);
        } while (!feof($handle));
        // Unlock it.
        flock($handle, LOCK_UN);
        // Return it unserialised.
        return $this->prep_data_after_read($data);

Fix:

1) Comment out the following lines:

flock($handle, LOCK_SH);
$data = '';

2) Save lib.php

Reload site... Voila!

Okay, so this appears to have fixed the ability to log into the site, but post login the same error appears, with an option to continue, and all functions normally afterwards. See screen shot.

I am going to examine the debug and post.

All issues are repaired. Post the fix mentioned above which allowed me to at least get into the site, it was a simple matter of clearing all caches by way of Site Administration->Development->Purge All Caches

Once I completed this activity, the clog in the .php caching was resolved on all counts and all was normal.

Thanks Michael,

clearing all catches worked for me, I was getting an error in both PayPal and Manage enrol plugins.

Clearing the the catches as you instructed;

"clearing all caches by way of Site Administration->Development->Purge All Caches"

cleared the error message.

Thanks,

Dennis Maloney

Removing the cache worked for me.

If you have no access the server from web browser, try using direct URL to purging cache, http://"your-server-address"/admin/purgecaches.php. You will need to login using an admin account. If that does not work or cannot login, use the cli from the server console terminal. Run this command line "sudo -u apache php admin/cli/purge_caches.php" in the Moodle directory.

Hope it helps.

Thanks to all

The Problem solved.

Thanks

Srinivas

Yes, the same for me. Clearing all catches worked for me

clearing all catches worked for me too

Thank you so match

For me too !

Thank you.

Thank you. Clearing the cache worked for me, too.

The problem happened after a site downtime (due to power outage). The site seemed to work ok, but many features were failing due to this error, eg. manual user enrolls, searching in admin menu etc.

Thanks for posting even when no one answered you.

Had same problem and resetting the cached fixed.

Carolyn

Brilliant - purging all caches also resolved my issue which was the same error occurring while trying to open up a course site after a power outage. (Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write.)

THANK YOU for taking the time to document your resolution Michael - this is why I love Moodle and the forums

Thank you Michael Otto. This helped me as well.

David Maldonado

thanks

Just wanted to say thank you for sharing this information.

I too had the same error on all 4 moodle sites on the same server. I recently upgraded the server environment to WAMP 31 and moodle 3.4.

The error message had me thinking DB, but was very happy to purge the caches and be rid of the issue.

I did not even realize I could still log in. When saw the error, I assume DB, no login.

Hi Michael,

I had the almost the same problem too. I had to restore a backup VM that has a Moodle on it and encounter the same error message.

Tried your suggestion of commenting the code out but i got more errors.

Anyway, i think i resolved it by purging the caches

There is a file locate in admin/cli/purge_caches.php

What i did was to ran the it as a command in the server prompt

sudo -u www-data /usr/bin/php admin/cli/purge_caches.php

Didn't get the same error but somthing similar ... don't re-call what it was now, but ... took a different approach and solved the problem.

The approach if you have command line access to /moodledata folder. Manually remove the cache folder and it's contents. I re-created an empty cache folder with ownerships/permissions for apache.

The logged onto the Moodle instanace. Fact I was admin it populated cache with some items right away. Use the Site Admin menu search box for 'cache'. The page that was rendered pulled up all items related. Scrolled to the bottom of the form and click 'Save'. Moodle re-populated some more of the subfolders in moodledata/cache/

One could also purge all caches from there.

Ran the cron.php file. That populated simplepie RSS feeds. Edited an item that would bring up TinyMCE editor. Didn't really edit anthing, just got into that edit mod to get TinyMCE in the cache. Eventually, cache caught up with all that needed to be there.

'spirit of sharing', Ken

Thank you as well Ken. In earnest, I didn't know enough about the moodle file structure and the relevant content created to know if doing such a thing would be harmful. Noted for future reference.

Genuinely appreciate the feedback an help

Mike

Thank you as well Ken. In earnest, I didn't know enough about the moodle file structure and the relevant content created to know if doing such a thing would be harmful. Noted for future reference.

Genuinely appreciate the feedback an help

Mike

Thanks Ken, it really worked, i just deleted the cache folder in sitedata and re-created it and gave the permissions and tadaaa

Thanks a lot Mr. Ken, it really did the trick!

Thanks fort the tip. I ran into similar problem after power outage.

deleted cache folder in moodledata, recreated with www-data permissions.

The icons and nested structures looked cluttered but, purging caches form administration->development did the trick.

N.B: I could not use that purge cache option before not even from the command line as mentioned by others. it would give me the same error.

Thanks a lot Ken, the solution that you gave to the problem was the one that worked for me because what mike said before was not useful, but igaul thank all that make moodle not a tragedy but rather a platform more and more Attractive

Thank you Ken - this happened to me today and following your instructions I was able to restore functionality. The other solutions here were not effective, but rebuilding the cache folder was.

Ken,

Thanks for posting this method. In my case I could not login at all with any account, and I had no command line access. I renamed the cache folder in moodledata, and moodle immediately created a new cache folder and began populating it. So I did not have to create a new cache folder. All works fine now.

John

Hey Samuel

Thank you - that solution seems elegant - a lot less convoluted than the one I discovered. I should have figured there was a .php file with the relevant purge code.

Noted for "next time"

Thank you!

Mike

Yeah. Not sure if it's the right way. But it seems to work

I too can't figure out the file structure of moodledata to be brave enough to delete the "correct" files... :p

Maybe need to read up some more documentation.

Thanks for posting Samuel, Michael and Ken

In my case, I recived this report in my command line, when I used purge_caches.php

I had to delete the cache folder of moodledata.

Thank you all so much

I was in tears !!!! literally

this saved my life

God bless you all for the "spirit of sharing" !!!

Awesome

The last 2 days my Cron Daemon reports the following:

PHP Notice:

Undefined variable: data in /var/www/vhosts/p-sii.nl/httpdocs/cache/stores/file/lib.php on line 368 !!! Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write. !!!

I have commented out the lines as instructed and reloaded the site. However the error remains.

Having limited knowledge of php I don't know which variable in line 368 is undefined or which part of the code is in error.

Can anyone help please?

Thank you in advance,

Pieter

Update.

The error code concerning line 368 has disappeared.

The original error however remains though I have tried to purge all caches.

Problem solved by removing cache folder.

Thanks Michael

Hi Guys,

I've got a very similar issue for my install (2.5.1) too: http://elss.dtwd.wa.gov.au/course/index.php

I've tried purging the cache but that hasn't helped.

When when developer mode is on I get the following too:

Debug info:
Error code: codingerror

Stack trace:

line 472 of \cache\stores\file\lib.php: coding_exception thrown
line 375 of \cache\stores\file\lib.php: call to cachestore_file->prep_data_after_read()
line 295 of \cache\classes\loaders.php: call to cachestore_file->get()
line 1350 of \cache\classes\loaders.php: call to cache->get()
line 1125 of \cache\classes\loaders.php: call to cache_application->get()
line 245 of \cache\classes\factory.php: call to cache_application->__construct()
line 183 of \cache\classes\factory.php: call to cache_factory->create_cache()
line 171 of \cache\classes\loaders.php: call to cache_factory->create_cache_from_definition()
line 555 of \lib\coursecatlib.php: call to cache::make()
line 981 of \lib\coursecatlib.php: call to coursecat::get_tree()
line 739 of \course\manage.php: call to coursecat->get_children()
line 342 of \course\manage.php: call to print_category_edit()

Any ideas?

Thanks,
Scott

I lie, purging all caches worked.

Exclua a pasta cache em seu moodledata.

Simple way to solve the problem : delete moodledata cache.

Command line: rm -rf /var/moodledata/cache

You can also delete the second cache folder inside moodledata named localcache

same method:

Command line: rm -rf /var/moodledata/localcache

...and moodle will work like never before! ;)

Works great! Thanks.

(I faced with this error when I limited some usage of server. But solved in this way)

Purge cache from a Windows server

I ran in to this again, I tried clearing the caches but it failed giving me an error message regarding not being able to run the command.

I went around the problem by downloading a fresh copy of the course, then I copied all my plugins, blocks and modules to the folder and replaced my code and it fixed the problem.

I wonder what is the root cause of this and how to prevent it from happening in the future.

DM

delete the cache folder in moodle data directory.

it will work

I found the same error today .

As I am a user that pays for a server , I cannot run a script in the apache server.

I also found that the other instructions were not exactly clear ?

So to solve the issue

1) I went into the server and found the folder that I had installed Moodle in ( your folder)

2) I opened it and found the folder called "data" opened it to see the "cache " folder and then instead of deleting it to start with, I simply renamed it ( why because it took the safety option first.

3) This solved the issue and I had access to both front and (admin) .. sections..

4) moodle of cause then generates a new cache folder and away we went.

5) I then tried logging in to Moodle admin and did a test purge from there...

I think if you are trying to lend a little advice - you might presume that people might not be as clever as you. ( that might include me)

Ok.. I hope this works for me..

General help

Help required! Getting Error:Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write.