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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def refresh_db(**kwargs):
    '''
    Update ports with ``port selfupdate``

    CLI Example:

    .. code-block:: bash

        salt mac pkg.refresh_db
    '''
    # Remove rtag file to keep multiple refreshes from happening in pkg states
    salt.utils.pkg.clear_rtag(__opts__)
    cmd = ['port', 'selfupdate']
    return salt.utils.mac_utils.execute_return_success(cmd)