Praj's Blog

PHP database can’t connect to localhost but works

There are many reasons for this, so first check that MySQL/MariaDB is running properly, that you are using the correct credentials and that the the appropriate user@localhost has access.

Also check you aren’t using skip-name-resolve and bind-address in your my.cnf file if accessing from outside of the localhost. These are things you will find with a google search.

Apart from this one other reason why will work and localhost will not work is if you are using something other than the default socket=/var/lib/mysql/mysql.sock location in your my.cnf.

If that is the case, you’ll need to update the relevant default_socket= parameter in php.ini (for each driver) to match that socket – see the entries under my.cnf [mysql] and [mysqld] sections for the socket parameter. This is more likely to occur if you are using MariaDB for example.

$_SESSION global is empty

If you find that your global $_SESSION variable is empty there can be several reasons, here are a few:

  • The session.save_path is invalid (does not exist) or is not writable.
  • The session.cookie_secure is set to true but you not using a secure site (SSL/https).
  • The session.cookie_domain is set to a domain that does not match your site – very common if setting up a dev or test environment from a production site with a public domain.

PHP Session Save Path

You can find the session.save_path through php info or using the command line:

php -i | grep save_path

E.g. /var/lib/php/session

Once you have that, you clear PHP sessions by going into that path and clearing out the relevation session files.

Find constants in your PHP code base

The following grep command will search for any constants such as define('CONSTANT', 1) within your PHP code base so you can see their values. Useful as many applications store the constant’s value in the database and not the constant’s friendly name.

This requires regular expressions, hence the use of egrep.

egrep --include *.php "(define)(.*)" -r *

SublimeLinter (with PHP)

SublimeLinter is a great syntax/error checking plugin for SublimeText.

Here are the steps to get it working (for example with PHP):

Note if you get stuck, use


to open your sublime text console and look for any errors. Also check the very comprehensive documentation:

Undefined index: HTTP_HOST

Helped out a colleague with this issue. It can occur if you are trying to browse to a local site on your machine via https instead of http (among many other reasons). In this particular case it was due to https-everywhere extension in Firefox. So just make sure you are really going
to a http version of the site.

Another related error you might see is:

SSL received a record that exceeded the maximum permissible length. 
(Error code: ssl_error_rx_record_too_long)

Which immediately tells you your browser is trying to perform a https request.

Disallowed Key Characters Error

I loaded a CodeIgniter site today and received a blank page with just the message “Disallowed Key Characters”.

There are myriad of scenarios that can cause this to occur. In my particular example, it occurred due to the fact that my application/config.php file had the following set:

$config['cookie_prefix'] = "<CHANGEME>_";

I had put that in as a placeholder, but the “<” and “>” symbols are not allowed in this particular config value and throw this error. There are other symbols that will also cause this, so something to watch out for.

After you change this, remember to clear your browser cookies too.

PHP Syntax Check Multiple PHP files

Found this pretty cool link to how to syntax check multiple PHP files by passing the results of a find to php -l.

I’ve extended this and grepped out any files that pass syntax checking so you are just left with the errors. Here’s the full command in all its glory:

$ find . -name "*.php" -print0 | xargs -0 -n1 -P8 php -l | grep -v "No syntax errors detected"

Force PHP errors to display

If you are really stuck and not getting any useful information regarding PHP errors in your log files, then you can the following to the relevant PHP file and it will display those errors on screen:


ini_set("display_errors", 1);

Very handy when you are really stuck!

Nothing written to PHP error log

Just a quick checklist if you aren’t getting anything written to the PHP error log on your server:

  • In php.ini, do you have error_reporting set to E_ALL ?
  • In php.ini, do you have log_errors set to On ?
  • In php.ini, do you have track_errors set to On ?
  • Have you specified a valid file / location for error_log
  • Does the user that starts PHP (Apache) have relevant permissions and ownership to write to that error_log file ?
  • Does your application have an override set in .htaccess or php.ini for any of the above?
  • Have you restarted PHP/Apache after making changes for these things to take effect?
  • What does php -i | grep error tell you regarding these settings?