This is really just a quick note. Much can be found on WordPress codex describing the steps when moving server, but this one caught me out.
I decided that I would move all my wordpress sites off my shared hosting reseller account to a VPS (Virtual Private Server).
As I had paid for WHM/Cpanel, it was fairly easy. I am actually glad I did, despite having been a professional unix system admin before the days of WHM/Cpanel it doesn’t half make things easy.
Anyway, all my accounts (about 8 sites) moved across easily then their was the inevitable one that ‘white screened’. So I spent a good hour or so, recopying, checking it worked on the original reseller account, updating wordpress and the plugins to the latest and re-copying.
Then when it still wouldn’t work, I finally resorted to checking the php,ini settings. And there is was, memory_limit on my Reseller was set to 64Mb and the default set up on my VPS was only 32Mb. A few seconds to mak ethe change and all was well. memory_limit is there to control badly written scripts from grabbing all the server memory, however 32Mb is sometimes too small for WordPress with premium themes and some bigger plugins.
Moral of the story, check your php.ini settings when moving server.
If you don’t know how, here is a simple way, create a file called phpinfo.php and add the following
<?php phpinfo(); ?>
upload it to you web root and run it e.g. www.mydomain.com/phpinfo.php