如何从 systemd 用户服务访问会话 D-Bus？答案

【问题标题】：How to access session D-Bus from systemd user service?如何从 systemd 用户服务访问会话 D-Bus？
【发布时间】：2016-12-02 02:29:02
【问题描述】：

我有运行 shell 脚本的用户服务，它试图像这样访问我的会话的锁屏状态：

# Test Unity screen-lock:
isLocked() {
    isLocked=$(gdbus call -e -d com.canonical.Unity -o /com/canonical/Unity/Session -m com.canonical.Unity.Session.IsLocked)
}

lock() {
  if [[ $isLocked == "(false,)" ]]; then                                                                                                     
        gnome-screensaver-command -l
  elif [[ $isLocked == "(true,)" ]]; then                                                                                                
        exit 1
  fi
exit 0
}

问题是服务“是每个用户的进程，而不是每个会话”，我不知道如何访问会话 dbus：

GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name com.canonical.Unity was not provided by any .service files

【问题讨论】：

这段代码中是否设置了 DBUS_SESSION_BUS_ADDRESS 变量？
不，不是。应该是？
据我所知，它需要连接到总线，并且 pam_systemd 应该在您登录时设置它。如果没有设置，则会启动一个新的 dbus，您将无法与其他事物交谈。我对这些都不太了解，所以不要相信我的话。

标签： ubuntu dbus systemd

【解决方案1】：

我也遇到了同样的问题，但我的研究一无所获。如果有人能找到更好的方法来查询 Unity 的锁定状态，我很想听听。

我最近了解了命名管道，当时我想知道我可以用这种东西做什么。事实证明，这个问题恰好是一个完美的应用程序。

创建以下脚本...

#!/bin/bash
# this script is meant to be called in two different ways.
# 1.    It can be called as a service by passing "service" as the first argument. In this 
#   mode, the script listens for requests for lock screen status. The script should be
#   run in this mode with startup applications on user logon.
# 2.    If this script is called without any arguments, it will call the service to request
#   the current lock screen status. Call this script in this manner from your user 
#   service.

# this will be the named pipe we'll use for requesting and receiving screen lock status
pipe="/tmp/lockscreen-status"

if [ "$1" == "service" ]; then
    # setup the named pipe
    rm "$pipe"
    mkfifo "$pipe"

    # start watching for requests
    while true
    do
        # watch the pipe for trigger events requesting lock screen status
        read request < "$pipe"

        # respond across the same pipe wit the current lock screen status
        gdbus call -e -d com.canonical.Unity -o /com/canonical/Unity/Session -m com.canonical.Unity.Session.IsLocked | grep -oP "(true)|(false)" > "$pipe"
    done
else
    # make sure the pipe exists
    if [ ! -e "$pipe" ]; then
        echo "This script must started in service mode before lock status can be queried."
        exit
    fi

    # send a request for screen lock status and read the response
    touch "$pipe"
    read status < "$pipe"

    [ "$status" == "" ] && status="This script must started in service mode before lock status can be queried."

    # print reponse to screen for use by calling application
    echo $status
fi

如 cmets 中所述，您需要以两种方式调用此脚本。当您的用户登录时，以服务模式启动此脚本。我使用“启动应用程序”程序来调用脚本，但它的调用方式并不重要，只要它在登录时由您的用户帐户调用即可。然后在您的用户服务中，只需调用此脚本，如果屏幕被锁定，它将返回“true”，如果屏幕被解锁，它将返回“false”。

【讨论】：