Why drush fails to rsync between my two local instances?
You cannot change the file timestamps or change permissions by being a member of a group, you have to be the file owner, or root. If you cannot be the other of that file, you might need to avoid trying to set permissions at all.

So you may try to modify your drushrc file (e.g. sites/default/drushrc.php) and add the following arguments for rsync command:

$command_specific['rsync'] = array('mode' =&gt; 'rlptzO', 'verbose' =&gt; TRUE, 'no-perms' =&gt; TRUE);


If running rsync on remotes, edit your aliases.drushrc file (e.g. sites/default/aliases.drushrc.php) and add something like:

$aliases['mysite.dev'] = array(
    // here are your settings such as uri, root, remote-host, etc.

    'command-specific' =&gt; array (
      'rsync' =&gt; array('mode' =&gt; 'rlptzO', 'verbose' =&gt; TRUE, 'no-perms' =&gt; TRUE),
    ),
);