drupal Archives - Complete, Concrete, Concise

WordPress Generating Core Dumps

richardsplanet — Sun, 01 Sep 2013 19:52:59 +0000

Between 30-August-2013 and 01-September-2013, Complete, Concrete, Concise had its web hosting suspended with a demand that the WordPress installation be deleted.

Not wanting to delete my installation and then reinstall (and hopefully restore all data correctly), I investigated.

Note: this problem and solution is likely the same for any PHP based application – like Joomla! or Drupal.

Symptoms

Most likely, your web hosting provider will inform you that your account has been suspended because your WordPress (or other PHP based application) is generating a lot of core dumps and playing havoc with their server. In my case, I was asked to delete my WordPress installation.

Alternately, you may notice there are a lot of core.xxxx (xxxx being a four digit number) files in your WordPress directory.

The Cause

There may be other causes for core dumps, but this is what was causing mine.

When your error_log file gets to be 2,147,483,647 bytes long, PHP will start crashing and generating core dumps. This is because PHP cannot handle files larger than 2GB.

error_log is where PHP stores messages about any errors it encounters.

The most common cause of errors is a corrupt MySQL database file.

I suspect this is a fairly common problem but I could only find it mentioned here.

PHP’s failure in dealing with files larger than 2³¹ – 1 bytes long is documented here (although, the expression “unexpected behaviour” doesn’t really do it justice). To be fair, the PHP documentation claims this is only a problem on 32-bit systems – however, since I don’t know if my web host is running a 32 or 64 bit version of Linux, I can’t say anything other than “it is really stupid to not fail gracefully at a known hard limit”.

The Fix

When your account is suspended, you will probably only have ftp access.

Delete the file error_log.
rename index.php to something else (xxx_index.php is good)
inform your hosting provider that:
1. you suspect the problem was PHP’s inability to handle and error_log larger than 2GB and you have deleted it
2. you have deactivated your WordPress account by renaming index.php
3. you would like access to your account restored so you can run MySQL applications to check and repair your database if necessary
Fix the database (if it is corrupted). Instructions for checking and repairing a database can be found here.
restore the name of the file in step (2) back to index.php
go to your website and browse a few pages.
verify that core.xxxx files are not being generated. If they are being generated, than you probably have some other problem.
verify that the file error_log is not being generated. If it is being generated, it is a good idea to look at it and see what errors are occurring. Depending on how quickly error_log is growing, it might be a good idea to suspend your site again by renaming index.php

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When Your Website Stops Working Properly, it may be a Corrupt Database

richardsplanet — Thu, 14 Mar 2013 01:02:25 +0000

This tutorial is for people using a web host that uses the cPanel interface (version 11.34.1).

Instructions may be the same for other versions or interfaces, but not guarantee is made.

When we set up a website, we expect it to keep working. Maybe we have to apply periodic updates and patches, but, in general, we expect it to keep working.

Unfortunately, after a while, you may find your website, powered by Joomla!, WordPress, Drupal or some other CMS, stops working correctly.

Common symptoms include:

I have experienced all these on Joomla! and WordPress powered sites I run.

Some or all of the comments disappear
Some or all of the content disappears
You get database connection errors
Your layout / template starts looking a bit funny
Pages you know exist start generating HTTP 404 Not Found errors
URLs start looking funny

A common cause of these problems is a corrupted MySQL database.

There may be other reasons for these (and other) problems, but a corrupt database is one of them.

Checking if the Database is Corrupted

1) Log into your web hosting control panel. This is not your website’s admin panel. For this tutorial, I am assuming it is cPanel. It might look something like this (this is how mine looks):

2) Click on MySQL® Databases:

3) Locate the section titled Modify Databases. On the line titled Check DB: select the database to check from the dropdown box. Click the button Check DB (located on the right side):

Note: if you only have one website hosted, then choosing the appropriate database is easy. If you have multiple sites, then you will have to figure out which database belongs to which site.

It does not hurt to check them all.

4) Examine the report generated. There should be no errors. If there are errors, then your database is corrupted and needs to be repaired.

Note: if your website is a busy website, you may get errors (usually something along the lines of table not closed) because the database is in the middle of being used. If you run the test again and the errors go away, then it probably is because the database was in use and not because the database is corrupted.

This is an example of a corrupted WordPress database:

This is an example of a corrupted Joomla! database:

Repairing the Database

This is not the recommended way, but it should work in most cases.

Most often, the problem is not with the actual database itself, but with the index files used to access the database.

You can read more about how it works here (warning, external site).

The preferred method is to restore the corrupted database with an up to date backup of your database. This supposes you have an up to date backup.

1) Locate the section titled Modify Databases. On the line titled Repair DB: select the database to repair from the dropdown box. Click the button Repair DB (located on the right side):

This will begin a repair operation on the database.

After the operation has completed, check the database again. If there is still a problem, then run Repair DB again. I have, sometimes had to run it twice.

Afterwards, it does not hurt to check your site and content to ensure everything is ok. This is a lot of work if you have many articles to check.

Restoring the Database from a Backup

1) Click on Backups (located on your cPanel home page):

2) Locate the section called Restore a MySQL Database and click on Browse… and select the backup database from your computer. Click on Upload to upload the database.

During this process, not much may seem to be happening.

The backup database has to be uploaded from your system to your service provider.

Once it is uploaded to the service provider, the existing database is rebuilt from the uploaded one.

The whole process looks something like this:

What you see happening is a whole bunch of MySQL transactions that delete the contents of the old database and replace it with the contents of the backup database.

If you are interested in database development, this is a good instructional example of some MySQL commands in action.

Restoring from backup, means you will lose any changes that occurred from the time of the backup until the time of the database corruption. Normally, this will be things like: comments, registrations, traffic information (if thissort of thing is stored in the database). While these things vary in importance, I believe the most important thing is the content.

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