Search code examples
pythonsessionrandomcherrypy

cherrypy /dev/urandom (or equivalent) not found -- error

I am running a cherrypy 3.2.0 server with Python 2.5.1, which gives the following error every few days on any instruction from UI until it is killed and re-started:-

[29/Mar/2012:06:37:57] HTTP Traceback (most recent call last):
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/_cprequest.py", line 636, in respond
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/_cprequest.py", line 97, in run
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/_cprequest.py", line 57, in __call__
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/lib/sessions.py", line 757, in init
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/lib/sessions.py", line 162, in __init__
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/lib/sessions.py", line 190, in _regenerate
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/lib/sessions.py", line 204, in generate_id
File "/usr/lib/python2.5/site-packages/CherryPy-3.2.0-py2.5.egg/cherrypy/_cpcompat.py", line 264, in random20
File "/usr/lib/python2.5/os.py", line 733, in urandom
NotImplementedError: /dev/urandom (or equivalent) not found

_cpcompat.py has following piece of code which suggests that there is a fallback on random.random in case cherrypy is not able to read /dev/urandom, but doesn't seem to be falling back on it.

try:
    os.urandom(20)
    import binascii
    def random20():
        return binascii.hexlify(os.urandom(20)).decode('ascii')

except (AttributeError, NotImplementedError):
    import random
    # os.urandom not available until Python 2.4. Fall back to random.random.
    def random20(): 
        return sha('%s' % random.random()).hexdigest()

Following is the code snippet from os.py, relevant in the context:-

if not _exists("urandom"):

    def urandom(n):
        """urandom(n) -> str

        Return a string of n random bytes suitable for cryptographic use.

        """
        try:
            _urandomfd = open("/dev/urandom", O_RDONLY)
        except (OSError, IOError):
            raise NotImplementedError("/dev/urandom (or equivalent) not found")
        bytes = ""
        while len(bytes) < n:
            bytes += read(_urandomfd, n - len(bytes))
        close(_urandomfd)
        return bytes

At the same time when cherrypy is not able to read /dev/urandom, the following code snippet is working fine :-

python -c "import os;fd = open('/dev/urandom', 'r');print fd.read(5);fd.close()"

I have two questions:-

  1. Why is cherrypy throwing not implemented error when I am able to read random bits from /dev/urandom
  2. Why is _cpcompact.py not executing the except part when os.py is raising NotImplementedError.
Solution

  • This is not an answer either, however, in my experience this NotImplementedError is erroneous but shows up when 'too many files' are open errors start showing up after a multiprocessing Processes start throwing uncaught exception, left to dangle forever in child threads or child processes.

    I would start debugging further up the stack and see if there are buried or silent exceptions thrown by a Process

    Here's an example of my stack trace when I start seeing this error

    Exception in thread Plotter:
Traceback (most recent call last):
  File "threading.pyc", line 532, in __bootstrap_inner
  File "plotters/edge.pyc", line 459, in run
  AttributeError: 'error' object has no attribute 'error'

OSError: [Errno 24] Too many open files
  File "multiprocessing/connection.pyc", line 150, in Client
  File "multiprocessing/connection.pyc", line 370, in deliver_challenge
    None
  File "os.pyc", line 756, in urandom
NotImplementedError: /dev/urandom (or equivalent) not found

    My AttributeError produced, eventually... the /urandom not found imlp error