PHP Connection failed: SQLSTATE[HY000] [2002] Connection refused

I found the reason why the connection was not working, it was because the connection was trying to connect to port 8888, when it needed to connect to port 8889.

$conn = new PDO("mysql:host=$servername;port=8889;dbname=AppDatabase", $username, $password); 

This fixed the problem, although changing the server name to localhost still gives the error.

Connection failed: SQLSTATE[HY000] [2002] No such file or directory

But it connects successfully when the IP address is entered for the server name.

In my case MySQL sever was not running. I restarted the MySQL server and issue was resolved.

//on ubuntu server
sudo /etc/init.d/mysql start

To avoid MySQL stop problem, you can use the "initctl" utility in Ubuntu 14.04 LTS Linux to make sure the service restarts in case of a failure or reboot. Please consider talking a snapshot of root volume (with mysql stopped) before performing this operations for data retention purpose[8]. You can use the following commands to manage the mysql service with "initctl" utility with stop and start operations.

$ sudo initctl stop mysql
$ sudo initctl start mysql

To verify the working, you can check the status of the service and get the process id (pid), simulate a failure by killing the "mysql" process and verify its status as running with new process id after sometime (typically within 1 minute) using the following commands.

$ sudo initctl status mysql         # get pid
$ sudo kill -9 <pid>                # kill mysql process
$ sudo initctl status mysql         # verify status as running after sometime

Note : In latest Ubuntu version now initctl is replaced by systemctl