xmodmap: unable to open display '' Error: Couldn't connect to XServer passing null display

/*********************************************************************************
 *  xmodmap:  unable to open display '' Error: Couldn't connect to XServer passing null display
 * 说明：
 *     fluxbox窗口管理器通过startx无法执行起来。
 *
 *                                              2017-12-19 深圳 南山平山村 曾剑锋
 ********************************************************************************/

一、参考文档
    1. How to make startx use alternate xinitrc?
        https://unix.stackexchange.com/questions/6274/how-to-make-startx-use-alternate-xinitrc

二、执行方法
    # cat S80startx
        #! /bin/sh
        
        ... 
        case "$1" in
          start)
                printf "Starting $DESC: "
                startx /root/.xinitrc &
                echo "OK"
                ;;
          *)
                echo "Usage: $0 {start}" >&2
                exit 1
                ;;
        esac
        
        exit 0