Different CUDA versions shown by nvcc and NVIDIA-smi

Question

I am very confused by the different CUDA versions shown by running which nvcc and nvidia-smi.

I have both cuda9.2 and cuda10 installed on my ubuntu 16.04. Now I set the PATH to point to cuda9.2. So when I run :

 $ which nvcc
 /usr/local/cuda-9.2/bin/nvcc

However, when I run

$ nvidia-smi
Wed Nov 21 19:41:32 2018       
+-----------------------------------------------------------------------------+
| NVIDIA-SMI 410.72       Driver Version: 410.72       CUDA Version: 10.0     |
|-------------------------------+----------------------+----------------------+
| GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile Uncorr. ECC |
| Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util  Compute M. |
|===============================+======================+======================|
|   0  GeForce GTX 106...  Off  | 00000000:01:00.0 Off |                  N/A |
| N/A   53C    P0    26W /  N/A |    379MiB /  6078MiB |      2%      Default |
+-------------------------------+----------------------+----------------------+

+-----------------------------------------------------------------------------+
| Processes:                                                       GPU Memory |
|  GPU       PID   Type   Process name                             Usage      |
|=============================================================================|
|    0      1324      G   /usr/lib/xorg/Xorg                           225MiB |
|    0      2844      G   compiz                                       146MiB |
|    0     15550      G   /usr/lib/firefox/firefox                       1MiB |
|    0     19992      G   /usr/lib/firefox/firefox                       1MiB |
|    0     23605      G   /usr/lib/firefox/firefox                       1MiB |

So am I using cuda9.2 as which nvcc suggests, or am I using cuda10 as nvidia-smi suggests?

I saw this answer but it does not provide direct answer to the confusion, it just asks us to reinstall the cudatoolkit, which I already did.

Answer 1

CUDA has 2 primary APIs, the runtime and the driver API. Both have a corresponding version (e.g. 8.0, 9.0, etc.)

The necessary support for the driver API (e.g. libcuda.so on linux) is installed by the GPU driver installer.

The necessary support for the runtime API (e.g. libcudart.so on linux, and also nvcc) is installed by the CUDA toolkit installer (which may also have a GPU driver installer bundled in it).

In any event, the (installed) driver API version may not always match the (installed) runtime API version, especially if you install a GPU driver independently from installing CUDA (i.e. the CUDA toolkit).

The nvidia-smi tool gets installed by the GPU driver installer, and generally has the GPU driver in view, not anything installed by the CUDA toolkit installer.

Recently (somewhere between 410.48 and 410.73 driver version on linux) the powers-that-be at NVIDIA decided to add reporting of the CUDA Driver API version installed by the driver, in the output from nvidia-smi.

This has no connection to the installed CUDA runtime version.

nvcc, the CUDA compiler-driver tool that is installed with the CUDA toolkit, will always report the CUDA runtime version that it was built to recognize. It doesn't know anything about what driver version is installed, or even if a GPU driver is installed.

Therefore, by design, these two numbers don't necessarily match, as they are reflective of two different things.

If you are wondering why nvcc -V displays a version of CUDA you weren't expecting (e.g. it displays a version other than the one you think you installed) or doesn't display anything at all, version wise, it may be because you haven't followed the mandatory instructions in step 7 (prior to CUDA 11) (or step 6 in the CUDA 11 linux install guide) of the cuda linux install guide

Note that although this question mostly has linux in view, the same concepts apply to windows CUDA installs. The driver has a CUDA driver version associated with it (which can be queried with nvidia-smi, for example). The CUDA runtime also has a CUDA runtime version associated with it. The two will not necessarily match in all cases.

In most cases, if nvidia-smi reports a CUDA version that is numerically equal to or higher than the one reported by nvcc -V, this is not a cause for concern. That is a defined compatibility path in CUDA (newer drivers/driver API support "older" CUDA toolkits/runtime API). For example if nvidia-smi reports CUDA 10.2, and nvcc -V reports CUDA 10.1, that is generally not cause for concern. It should just work, and it does not necessarily mean that you "actually installed CUDA 10.2 when you meant to install CUDA 10.1"

If nvcc command doesn't report anything at all (e.g. Command 'nvcc' not found...) or if it reports an unexpected CUDA version, this may also be due to an incorrect CUDA install, i.e the mandatory steps mentioned above were not performed correctly. You can start to figure this out by using a linux utility like find or locate (use man pages to learn how, please) to find your nvcc executable. Assuming there is only one, the path to it can then be used to fix your PATH environment variable. The CUDA linux install guide also explains how to set this. You may need to adjust the CUDA version in the PATH variable to match your actual CUDA version desired/installed.

Similarly, when using docker, the nvidia-smi command will generally report the driver version installed on the base machine, whereas other version methods like nvcc --version will report the CUDA version installed inside the docker container.

Similarly, if you have used another installation method for the CUDA "toolkit" such as Anaconda, you may discover that the version indicated by Anaconda does not "match" the version indicated by nvidia-smi. However the above comments still apply. Older CUDA toolkits installed by Anaconda can be used with newer versions reported by nvidia-smi, and the fact that nvidia-smi reports a newer/higher CUDA version than the one installed by Anaconda does not mean you have an installation problem.

Answer 2

nvcc is in the CUDA bin folder - as such check if the CUDA bin folder has been added to your $PATH.

Specifically, ensure that you have carried out the CUDA Post-Installation actions (e.g. from here):

1. Add the CUDA Bin to $PATH (i.e. add the following line to your ~/.bashrc)

export PATH=/usr/local/cuda-10.1/bin:/usr/local/cuda-10.1/NsightCompute-2019.1${PATH:+:${PATH}}

PS. Ensure the following two paths above, exist first: /usr/local/cuda-10.1/bin and /usr/local/cuda-10.1/NsightCompute-2019.1 (the NsightCompute path could have a slightly different ending depending on the version of Nsight compute installed...

2. Update $LD_LIBRARY_PATH (i.e. add the following line to your ~/bashrc).

export LD_LIBRARY_PATH=/usr/local/cuda-10.1/lib64\
                         ${LD_LIBRARY_PATH:+:${LD_LIBRARY_PATH}}

After this, both nvcc and nvidia-smi (or nvtop) report the same version of CUDA...

Answer 3

If you are using cuda 10.2 :

export PATH=/usr/local/cuda-10.2/bin:/opt/nvidia/nsight-compute/2019.5.0${PATH:+:${PATH}}

might help because when I checked, there was no directory for nsight-compute in cuda-10.2. I am not sure if this was just the problem with me or else why wouldn't they mention it in the official documentation.

Answer 4

I got the same problem discrepancy problem between the CUDA version displayed by nvcc (9.1) and nvidia-smi (11.2). In my case, the problem was due a nvcc instance in /usr/bin in addition to the nvcc instance of /usr/local/cuda/bin; Because /usr/bin came first in my PATH environment, my call to "nvcc" used the first nvcc instance (and thus displayed an old CUDA version). I thus fixed the problem by modifying the PATH env var. The command "nvcc -V" then correctly displayed a 11.2 CUDA version. (So it was just a nvcc display problem, not a CUDA installation problem).