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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 list of available packages from installed repos

    CLI Example:

    .. code-block:: bash

        salt '*' pkg.refresh_db
    '''
    # Remove rtag file to keep multiple refreshes from happening in pkg states
    salt.utils.pkg.clear_rtag(__opts__)
    cmd = 'xbps-install -Sy'
    call = __salt__['cmd.run_all'](cmd, output_loglevel='trace')
    if call['retcode'] != 0:
        comment = ''
        if 'stderr' in call:
            comment += call['stderr']

        raise CommandExecutionError(comment)

    return True