Question

I am using GeForce 8400M GS on Ubuntu 10.04 and I am learning CUDA programming. I am writing and running few basic programs. I was using cudaMalloc, and it kept giving me an error until I ran the code as root. However, I had to run the code as root only once. After that, even if I run the code as normal user, I do not get an error on malloc. What’s going on?

Answer 1

This is probably due to your GPU not being properly initialized at boot. I’ve come across this problem when using Ubuntu Server and other installations where an X server isn’t being started automatically. Try the following to fix it:

Create a directory for a script to initialize your GPUs. I usually use /root/bin. In this directory, create a file called cudainit.sh with the following code in it (this script came from the Nvidia forums).

#!/bin/bash

/sbin/modprobe nvidia

if [ "$?" -eq 0 ]; then

    # Count the number of NVIDIA controllers found.
    N3D=`/usr/bin/lspci | grep -i NVIDIA | grep "3D controller" | wc -l`
    NVGA=`/usr/bin/lspci | grep -i NVIDIA | grep "VGA compatible controller" | wc -l`

    N=`expr $N3D + $NVGA - 1`
    for i in `seq 0 $N`; do
        mknod -m 666 /dev/nvidia$i c 195 $i;
    done    

    mknod -m 666 /dev/nvidiactl c 195 255

else
    exit 1
fi  

Now we need to make this script run automatically at boot. Edit /etc/rc.local to look like the following.

#!/bin/sh -e
#   
# rc.local
#   
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#   
# In order to enable or disable this script just change the execution
# bits.
#   
# By default this script does nothing.

#
# Init CUDA for all users
#   
/root/bin/cudainit.sh

exit 0

Reboot your computer and try to run your CUDA program as a regular user. If I’m right about what the problem is, then it should be fixed.