Mysql Error – SQLSTATE[HY000] [2002]

I have come across the following error:
Mysql Error – SQLSTATE[HY000] [2002] No such file or directory
To solve this, you need to open up your php.ini file (mine was in /etc/). Look for the following line:

pdo_mysql.default_socket=/var/mysql/mysql.sock

If that line exists for you, try changing it to:

pdo_mysql.default_socket=/tmp/mysql.sock

Restart apache after saving, and that’s all I had to do.
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Multiple database connection on same credentials

If you are opening two separate connections to two different databases (but on the same host, and with the same user and password):

$db1 = mysql_connect($dbhost, $dbuser, $dbpass);
$rv = mysql_select_db($dbname1, $db1);
$db2 = mysql_connect($dbhost, $dbuser, $dbpass);
$rv = mysql_select_db($dbname2, $db2);

At this point, both $db1 and $db2 will have selected the database named by $dbname2.
The workaround is to require that the second MySQL connection is new:

$db1 = mysql_connect($dbhost, $dbuser, $dbpass);
$rv = mysql_select_db($dbname1, $db1);
$db2 = mysql_connect($dbhost, $dbuser, $dbpass, TRUE);
$rv = mysql_select_db($dbname2, $db2);

Now, $db1 should have selected $dbname1, and $db2 should have selected $dbname2.
See the book OpenCart 1.4 Template Design Cookbook.
See the book Joomla Mobile Development Beginners Guide

Multiple mysql connection with different servers

If you want to connect with different server with different credentials, then you need to connect with all the different servers and for each handle, you need to select the database and the queries.

$handle_db1 = mysql_connect("localhost","myuser","apasswd"); 
$handle_db2 = mysql_connect("127.0.0.1","myuser","apasswd"); 
$handle_db3 = mysql_connect("localhost:3306","myuser","apasswd"); 
$handle_db4 = mysql_connect("localhost","otheruser","apasswd"); 

We select the databases with each handle.

// give each handle it's own database to work with, permanently. 
mysql_select_db("db1",$handle_db1); 
mysql_select_db("db2",$handle_db2); 
mysql_select_db("db3",$handle_db3); 
mysql_select_db("db4",$handle_db4); 

And for querying the databases, we also set the handlers here.

//do a query from db1: 
$query = "select * from test"; $which = $handle_db1; 
mysql_query($query,$which); 

The below is for our second database.

//do a query from db2 : 
$query = "select * from test"; $which = $handle_db2; 
mysql_query($query,$which);

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See the book Joomla Mobile Development Beginners Guide

jQuery calls error callback on successful ajax request (status 200)

Sometimes though the jQuery ajax code block is right, it goes to the error condition block. we found no clues on this kind of strange behavior. Why this happened?
Actually, the request successfully reached the destination server, but when it returns the client expects one kind of response, but the server returns in different format. this produces the error.
It was expecting a Json response, but it was getting empty result, that's why it was showing on the error callback though it was a successful call.
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setting svn editor

I have come across the following error:
svn: None of the environment variables SVN_EDITOR, VISUAL or EDITOR are set, and no 'editor-cmd' run-time configuration option was found
To solve this problem, we need to add an editor for svn. we add the below line the bash profile file.

vim ~/.bash_profile
export SVN_EDITOR=vim

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POST with cross origin policy

If we try to submit a form or something using POST method in cross domain, then we face the cross origin error. We can mitigate this error by first setting the access control on the domain address and the access control header.

header('Access-Control-Allow-Origin: http://www.example.com');
//if you need cookies or login etc
header('Access-Control-Allow-Credentials: true');

After we submit the form, on the response header we set the followings:

if ($this->getRequestMethod() == 'OPTIONS')
{
  header('Access-Control-Allow-Methods: GET, POST, PUT, DELETE, OPTIONS');
  header('Access-Control-Max-Age: 604800');
  //if you need special headers
  header('Access-Control-Allow-Headers: x-requested-with');
  exit(0);
}

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PHP Fatal error: require_once(): Failed opening required 'system/startup.php'

I have found this error while working with an opencart shop. I am getting the following error into my error logs.
PHP Fatal error: require_once(): Failed opening required 'system/startup.php' (include_path='.:/usr/share/php:/usr/share/pear') in admin/index.php on line 15
Then I checked the config.php file and found that the path to the system file was wrong, so I placed the correct path to the file. and the error was gone.

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