Python multiprocessing: Permission denied

I'm getting an error when trying to execute python program that uses multiprocessing package:

  File "/usr/local/lib/python2.6/multiprocessing/__init__.py", line 178, in RLock
    return RLock()
  File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line 142, in __init__
    SemLock.__init__(self, RECURSIVE_MUTEX, 1, 1)
  File "/usr/local/lib/python2.6/multiprocessing/synchronize.py", line 49, in __init__
    sl = self._semlock = _multiprocessing.SemLock(kind, value, maxvalue)
OSError: [Errno 13] Permission denied

It looks like the user doesn't have permission to access shared memory. When executing with root privileges it works fine.

Is there any solution to run it as normal user(not root)?

Python version 2.6.2 , OS is Linux 2.6.18 (CentOS release 5.4) and it's VPS machine.

Solution 1:

For POSIX semaphores to work, the users need r/w access to shared memory (/dev/shm).

Check the permissions to /dev/shm. On my laptop (Ubuntu) it looks like this:

$ ls -ld /dev/shm
drwxrwxrwt 2 root root          40 2010-01-05 20:34 shm

To permanently set the correct permissions (even after a reboot), add the following to your /etc/fstab:

none /dev/shm tmpfs rw,nosuid,nodev,noexec 0 0

Haven't tried this, just copied from a forum post.

Solution 2:

In my OVH VPS Classic, this error was caused by a loop in /dev/shm and /run/shm. Both were symlinks linking to each other. So as root here is what I did:

# rm /dev/shm
# mkdir /dev/shm
# chmod 777 /dev/shm
# nano /etc/fstab

Then I modified the shm line from:

none /dev/shm tmpfs rw 0 0

To:

none /dev/shm tmpfs rw,nosuid,nodev,noexec 0 0

Restarted the server... And that fixed the problem! Alternatively you can mount shm manually:

# mount /dev/shm

Hope this helps :-)

Solution 3:

One simple solution without rebooting is

sudo chmod 777 /dev/shm

That solved my problem.