如何通过 Systemd DBus API 提取服务状态？答案

【问题标题】：How to extract service state via Systemd DBus API?如何通过 Systemd DBus API 提取服务状态？
【发布时间】：2017-09-15 22:16:36
【问题描述】：

我正在尝试使用Systemd D-Bus API 提取openvpn.service 状态。

In [1]: import dbus

In [2]: sysbus = dbus.SystemBus()

In [3]: systemd1 = sysbus.get_object('org.freedesktop.systemd1', '/org/freedesktop/systemd1')

In [4]: manager = dbus.Interface(systemd1, 'org.freedesktop.systemd1.Manager')

In [5]: service = dbus.Interface(systemd1, 'org.freedesktop.systemd1.Service')

In [6]: unit = dbus.Interface(systemd1, 'org.freedesktop.systemd1.Unit')

In [7]: unit.ActiveState('openvpn.service')
---------------------------------------------------------------------------
DBusException                             Traceback (most recent call last)
<ipython-input-7-22857e7dcbd7> in <module>()
----> 1 unit.ActiveState('openvpn.service')

/usr/local/lib/python3.4/dist-packages/dbus/proxies.py in __call__(self, *args, **keywords)
     68             # we're being synchronous, so block
     69             self._block()
---> 70             return self._proxy_method(*args, **keywords)
     71 
     72     def call_async(self, *args, **keywords):

/usr/local/lib/python3.4/dist-packages/dbus/proxies.py in __call__(self, *args, **keywords)
    143                                                   signature,
    144                                                   args,
--> 145                                                   **keywords)
    146 
    147     def call_async(self, *args, **keywords):

/usr/local/lib/python3.4/dist-packages/dbus/connection.py in call_blocking(self, bus_name, object_path, dbus_interface, method, signature, args, timeout, byte_arrays, **kwargs)
    649         # make a blocking call
    650         reply_message = self.send_message_with_reply_and_block(
--> 651             message, timeout)
    652         args_list = reply_message.get_args_list(**get_args_opts)
    653         if len(args_list) == 0:

DBusException: org.freedesktop.DBus.Error.UnknownMethod: Unknown method 'ActiveState' or interface 'org.freedesktop.systemd1.Unit'.

In [8]: manager.GetUnit('openvpn.service')
Out[8]: dbus.ObjectPath('/org/freedesktop/systemd1/unit/openvpn_2eservice')

In [9]: u = manager.GetUnit('openvpn.service')

In [10]: u.ActiveState
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-10-6998e589f206> in <module>()
----> 1 u.ActiveState

AttributeError: 'dbus.ObjectPath' object has no attribute 'ActiveState'

In [11]: manager.GetUnitFileState('openvpn.service')
Out[11]: dbus.String('enabled')

有一个ActiveState 属性，即contains a state value that reflects whether the unit is currently active or not。我已经成功阅读了UnitFileState，但是我不知道如何阅读ActiveState 属性。

【问题讨论】：

标签： python-3.4 dbus systemd

【解决方案1】：

在看了some random examples [more permanent link] 之后，我遇到了一些运气

import dbus
sysbus = dbus.SystemBus()
systemd1 = sysbus.get_object('org.freedesktop.systemd1',
    '/org/freedesktop/systemd1')
manager = dbus.Interface(systemd1, 'org.freedesktop.systemd1.Manager')
service = sysbus.get_object('org.freedesktop.systemd1',
    object_path=manager.GetUnit('openvpn.service'))
interface = dbus.Interface(service,
    dbus_interface='org.freedesktop.DBus.Properties')
print(interface.Get('org.freedesktop.systemd1.Unit', 'ActiveState'))

[编辑：] 记录版本，以防万一：

dbus.version == (1, 2, 14)
systemd 244 (244.1-1-arch)
Python 3.8.1

【讨论】：

【解决方案2】：

您可能需要调用dbus.Interface(sysbus.get_object('org.freedesktop.systemd1', u), 'org.freedesktop.systemd1.Unit') 并访问该对象的ActiveState 属性。您的代码当前尝试访问对象 path 上的 ActiveState 属性，该对象不是对象本身。

【讨论】：