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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 _active_mounts(ret):
    '''
    List active mounts on Linux systems
    '''
    _list = _list_mounts()
    filename = '/proc/self/mounts'
    if not os.access(filename, os.R_OK):
        msg = 'File not readable {0}'
        raise CommandExecutionError(msg.format(filename))

    with salt.utils.files.fopen(filename) as ifile:
        for line in ifile:
            comps = salt.utils.stringutils.to_unicode(line).split()
            ret[comps[1]] = {'device': comps[0],
                             'alt_device': _list.get(comps[1], None),
                             'fstype': comps[2],
                             'opts': _resolve_user_group_names(comps[3].split(','))}
    return ret