Popen does not work anymore with apache/wsgi and python 2.7.2?

Question

My django application that used to make some shell commands by using python subprocess.Popen does not work anymore since I upgrade to ubuntu to 11.10

To simplify the problem, I put the faulty code into the wsgi script :

import os
import sys

from subprocess import Popen,PIPE
p=Popen(['/usr/bin/id'],stdout=PIPE,stderr=PIPE)
comm=p.communicate()
print comm,p.returncode

os.environ['DJANGO_SETTINGS_MODULE'] = 'settings'
import django.core.handlers.wsgi
application = django.core.handlers.wsgi.WSGIHandler()

If I run this code directly by python, it works :

$ python -V
Python 2.7.2+
$ python django_wsgi.py 
('uid=1002(www) gid=1002(www) groups=1002(www)\n', '') 0

If I run this code by apache (I just put the relevant URL into a browser), in the apache log, I got :

[Tue Nov 29 11:34:38 2011] [error] ('', '') -6

What is this error '-6' ???

The problem is that with my development server (Ubuntu 10.04, almost the same apache/wsgi version, same apache configuration file, same environment variables, but with python 2.6.5) it works well :

[Tue Nov 29 11:29:10 2011] [error] ('uid=1000(www) gid=1000(www) groups=1000(www)\\n', '') 0

Do you know why Popen is not work through apache anymore with python 2.7 ?

Answer 1

Because latest Python 2.7 has a bug in it which causes fork run in sub interpreters to fail.

http://bugs.python.org/issue13156

Presuming only hosting the one WSGI application, force use of the main interpreter rather than a sub interpreter by adding to your Apache configuration:

WSGIApplicationGroup %{GLOBAL}