def get_username_list(cmdline_username, config):
    """Get a list of possible usernames.

    Usernames are select from the command line and the config file.
    """
    usernames = []
    if cmdline_username:
        usernames = [cmdline_username]
    else:
        username = config.get('default-username')
        if username:
            usernames = username.strip().split()
    return usernames