If you run WordPress on Red Hat Enterprise Linux (RHEL) or its free cousin CentOS then you will likely run into the following error after you have unpacked WordPress, installed it and tried to do your initial setup:
Error establishing a database connection
This either means that the username and password information in your wp-config.php file is incorrect or we can’t contact the database server at databasename. This could mean your host’s database server is down.
- Are you sure you have the correct username and password?
- Are you sure that you have typed the correct hostname?
- Are you sure that the database server is running?
If you’re unsure what these terms mean you should probably contact your host. If you still need help you can always visit the WordPress Support Forums.
You are not alone, this happens to everyone. If you do some searching on this you will find that pretty much no one has an answer for what is wrong. People running MySQL server locally already know the trick necessary to fix this problem but if you are running MySQL remotely, as I am, then you can be easily mislead into thinking that the fix does not apply to you, but it does.
The issue here, surprisingly, is that SELinux is enabled on the web server and is keeping the MySQL library from communicating with the MySQL server whether local or remote. Simply set SELinux to Permissive rather than Enforcing and voila, you should be working well.
The command to set SELinux to Permissive mode is:
setenforce 0
You can verify that the mode has changed correctly with:
getenforce
It is important to note that this SELinux issue (bug, I am told) does NOT affect the MySQL client but does affect PHP. So if you are testing your database connection with “mysql” and it works but WordPress throws the error than you are a prime candidate for this problem.
Also, be sure that PHP has the MySQL module installed:
yum install php-mysql
I have seen this issue on several versions of all of the software components but specifically just dealt with it in CentOS 5.2 with PHP 5.1.6 and WordPress 2.7.1.