dalsi pridavne info o CUDA troubleshootingu

README.md

@@ -226,7 +226,7 @@ SLURM will send you an email, when the job finishes. There are many other mail-t
 
 Charliecloud provides user-defined software stacks (UDSS) for HPC.
 It allows you to run nearly any software stack (like TensorFlow) on the cluster even it is not system-wide installed and available.
-All informations about Charlicloud can be found on its [Charliecloud documentation](https://hpc.github.io/charliecloud/) page.
+All informations about Charliecloud can be found on its [Charliecloud documentation](https://hpc.github.io/charliecloud/) page.
 
 ### Basic workflow
 
@@ -304,7 +304,7 @@ You may disable this by specifying `--no-home` option.
 Moreover, you may bind additional directories by using options `--bind=/some/dir`
 (which will appear as `/mnt/0` in your UDSS environment) or by `--bind=/source/dir:/dest/dir`.
 
-### Advanced techniques and notes
+### Advanced techniques, troubleshooting, and notes
 
 #### Builders
 
@@ -342,3 +342,14 @@ It can happen, executing `ch-fromhost` from the 3rd step will produce some error
 Ignore safely these errors, they do no harm to you.
 
 This warning/notice was contributed by Vít Kabele.
+
+#### CUDA is not working inside your UDSS
+
+If you suspect that CUDA is not working inside your container, run the `nvidia-smi` command from the container command line.
+If `nvidia-smi` prints the CUDA version correctly, then CUDA is functional. However, if it prints "ERR", CUDA does not work.
+
+In this case, follow the checklist:
+- Did you correctly import the CUDA libraries? See step 3 of the basic workflow.
+- Is `libcuda.so` (or `libcuda.so.1`) loadable? Check `LD_LIBRARY_PATH` environment variable inside your container. 
+If not set to the CUDA library directory, set it to the correct path, e.g. `export LD_LIBRARY_PATH=/usr/local/cuda/lib64`.
+Be careful, if the variable is already set to some additional paths.