Fatal error: Call to undefined function hash() in wp-includes/sess

Great catch, Ross!

Hello all.

The installation of the hash module has fixed the problem. Thanks to James and Ross for providing the clues to get this fixed.

Best,

–jody.

You’re welcome!

Given that this is a new requirement, the installer should run a short test to validate that hash is installed before it tries to update the site. Trivial test, and will prevent many broken sites.

It’s not actually a new requirement. The /wp-includes/session.php file is new, but hash() has been used by WordPress in other files since WordPress 2.0 was released in December of 2005.

Correcting my statement above, hash() was in WordPress 2.0, but removed sometime after, it was definitely not present in 3.9.

Why aren’t you able to upgrade from PHP 5.2.14?

If your hosting provider does not allow you to use a higher version of PHP, you should ask them why they’re keeping you on a version that was deprecated in January of 2011: https://en.wikipedia.org/wiki/PHP#Release_history

The solution suggested by beliwp worked for me. Thanks a lot.
But I am now struggling to install the hash module in php.
I do have access root. Can somebody of you give me a hint on how to do it??
Thanks everybody!

It depends on how your PHP system was installed in the first place. It seems that on some distributions, the php-hash functions (which are actually part of the PHP core) may be disabled.

Using your package management tool, see if there is a “php-hash” package available. Installing that should give you the necessary support. Honestly, it should have been installed as part of the PHP Common Core packages, but if it’s left out for some reason, then this could occur.