使用multiprocessing.Manager()时多用户出现权限被拒绝

Question

我有一个以管理员身份运行的程序，它需要创建一些线程，让这些线程以不同的用户身份运行。这部分现在运行得很好，但我需要一种方法来让子进程和父进程之间进行沟通。

当我尝试使用multiprocessing.Manager()来处理一些列表、字典、锁、队列等时，总是会出现权限被拒绝的错误，尤其是在那些权限降低的进程中。

有没有办法给某个用户或进程ID（PID）授予访问权限，以解决这个问题呢？

以下是我遇到问题的基本代码（以管理员身份运行）：

#!/usr/bin/env python
import multiprocessing, os
manager = multiprocessing.Manager()
problematic_list = manager.list()
os.setuid(43121) # or whatever your user is
problematic_list.append('anything')

结果：

root@liberator:/home/bscable# python asd.py
Traceback (most recent call last):
  File "asd.py", line 8, in <module>
    problematic_list.append('anything')
  File "<string>", line 2, in append
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 755, in _callmethod
    self._connect()
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 742, in _connect
    conn = self._Client(self._token.address, authkey=self._authkey)
  File "/usr/lib/python2.7/multiprocessing/connection.py", line 169, in Client
    c = SocketClient(address)
  File "/usr/lib/python2.7/multiprocessing/connection.py", line 293, in SocketClient
    s.connect(address)
  File "/usr/lib/python2.7/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
socket.error: [Errno 13] Permission denied
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/util.py", line 261, in _run_finalizers
    finalizer()
  File "/usr/lib/python2.7/multiprocessing/util.py", line 200, in __call__
    res = self._callback(*self._args, **self._kwargs)
  File "/usr/lib/python2.7/multiprocessing/managers.py", line 625, in _finalize_manager
    process.terminate()
  File "/usr/lib/python2.7/multiprocessing/process.py", line 137, in terminate
    self._popen.terminate()
  File "/usr/lib/python2.7/multiprocessing/forking.py", line 165, in terminate
    os.kill(self.pid, signal.SIGTERM)
OSError: [Errno 1] Operation not permitted

第一个异常似乎是这里最重要的。

Answer 1

Python（至少是2.6版本）使用一种叫做UNIX套接字的方式来进行通信，样子大概是这样的：

/tmp/pymp-eGnU6a/listener-BTHJ0E

我们可以获取这个路径，然后像这样修改它的权限：

#!/usr/bin/env python
import multiprocessing, os, grp, pwd
manager = multiprocessing.Manager()
problematic_list = manager.list()

fullname = manager._address
dirname = os.path.dirname(fullname)

gid = grp.getgrnam('some_group').gr_gid
uid = pwd.getpwnam('root').pw_uid # should always be 0, but you never know

os.chown(dirname, uid, gid)
os.chmod(dirname, 0770)

os.chown(fullname, uid, gid)
os.chmod(fullname, 0770)

os.setgid(gid)
os.setuid(43121) # or whatever your user is
problematic_list.append('anything')

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