bash - 从 /etc/rc.local 运行时，如何通过 dbus 获取空闲时间？

Question

我有一个基本的 bash 脚本，用于检查系统是否空闲超过一个小时，如果是，则将其关闭：

#!/bin/bash

while true; do
get_idle_time=`dbus-send --print-reply --dest=org.gnome.Mutter.IdleMonitor /org/gnome/Mutter/IdleMonitor/Core org.gnome.Mutter.IdleMonitor.GetIdletime`
idle_time=$(echo $get_idle_time | awk '{print $NF}')
if [[ $idle_time -ge 3600000 ]]; then
shutdown
fi
done

我添加了这个脚本，/etc/rc.local所以它总是处于活动状态：

#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.

bash /home/paulky/shutdown.sh

exit 0

虽然bash /home/paulky/shutdown.sh在我登录时从终端工作，但这样做/etc/rc.local似乎会阻止 Ubuntu 进入登录屏幕，并F2显示此错误消息无限重复：

Failed to open connection to "session" message bus: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11.

我已经尝试export DISPLAY=:0在脚本开始之前添加，但无济于事。