Use "pushkey" to set up your ssh keys to make sql-sync work

I have set aliases for my local and remote

$aliases['dev'] = array(
    'uri' => 'localhost',
    'root' => '/var/www/foo',
  );

$aliases['server'] = array(
    'remote-host' => 'example.com',
    'remote-user' => 'amitaibu',
    'path-aliases' => array(
      '%drush-script' => '/home/amitaibu/.drush/drush/drush',
      '%dump' => '/var/www/foo.example.com/foo.sql',
    ),
  );

$aliases['foo_server'] = array(
    'parent' => '@server',
    'uri' => 'http://foo.example.com',
    'root' => '/var/www/foo.example.com',
  );

The following works:

drush @dev sql-connect -v
drush @foo_server sql-connect -v

However If I try to drush sql-sync -v @foo_server @dev

I get an error:

Load alias @dev                                                       [notice]
Load alias @foo_server                                                    [notice]
Load alias @server                                                           [notice]
Undefined offset:  1 backend.inc:112                                         [notice]
Undefined variable: output backend.inc:119                                   [notice]
The command could not be executed successfully (returned: bash: drush:    [error]
command not found
, code: 127)
Error: no database record could be found for @foo_server               [error]
An error occurred at function : drush_sql_sync                            [error]
Command dispatch complete