using drush for upgrade drupal 6 to 7 - create alias problem I want to use drush for upgrade my drupal 6 to drupal7. i read this document. i have a problem with create alias. i have been doing this

1- create a subdomain in my plesk (create sub.domain.com)

2- go to /var/www/vhosts/domain.com/httpdocs and download this file and rename this to "aliases.drushrc.php"

3- remove aliases.drushrc.php content and replace with 

&lt;?php
$aliases['sub'] = array(
  'root' =&gt; '/var/www/vhosts/domain.com/sub',
  'uri' =&gt; 'sub.domain.com',
);
?&gt;

4- run command: drush @sub status and i get this error: 

The drush command '@sub status' could not be found.  Rundrush cache-clear drushto clear the commandfile cache if you have installed new extensions
Although the Drupal root is a valid place to store alias files, Drush will not be able to find the alias records described there until the Drupal root as been specified.  Therefore, drush @sub status has a chicken-and-egg problem; you want to use @sub to specify the Drupal root, but Drush won't load the alias file that defines @sub until the Drupal site it is defined in is bootstrapped.

To resolve this problem, move your aliases file to $HOME/.drush/aliases.drushrc.php.  Once you do that, then your status command will work.

You may define your 'onward' alias either in $HOME/.drush/aliases.drushrc.php, or in /var/www/vhosts/domain.com/httpdocs/aliases.drushrc.php, per your preference.