NCP-AIO Troubleshooting and Optimization Practice Question
An AI operations engineer is troubleshooting a multi-GPU training job that fails intermittently with a NCCL error: 'unhandled system error'. The job runs on a DGX-1 with eight V100 GPUs connected via NVLink. Which step should the engineer take first to resolve the issue?
⚠ Common exam trap
The trap here is jumping to hardware workarounds or reinstallations without first collecting diagnostic information that NCCL can provide.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set NCCL_DEBUG=INFO and reproduce the failure to capture detailed logs.
The first step in troubleshooting any NCCL error should be to gather detailed logs using NCCL_DEBUG=INFO. This provides visibility into the communication path and error specifics, enabling targeted fixes. Other options either mask the issue, involve unnecessary reinstallation, or reduce resources without diagnosis.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Disable NVLink by setting NCCL_P2P_DISABLE=1 to force PCIe communication.
Why it's wrong here
Disabling NVLink would force communication over PCIe, which has lower bandwidth and higher latency, likely degrading performance. It might mask a NVLink hardware issue but does not diagnose it and sacrifices performance. This is a workaround, not a diagnostic step, and should only be considered after confirming NVLink is faulty.
- ✗
Reinstall the NVIDIA driver and CUDA toolkit on all nodes.
Why it's wrong here
Reinstalling drivers and CUDA is a heavy-handed action that may not address the root cause and could introduce new issues. It should be a last resort after identifying a software corruption. Without diagnostic data, this is unlikely to resolve an intermittent NCCL error and may waste time.
- ✗
Reduce the number of GPUs used in the job to four to see if the error disappears.
Why it's wrong here
Reducing GPU count might avoid the error if it's related to specific GPUs or NVLink topology, but it does not diagnose the problem and reduces training throughput. It is a troubleshooting step that could provide a clue, but it is not the first action; gathering logs is more informative and less disruptive.
- ✓
Set NCCL_DEBUG=INFO and reproduce the failure to capture detailed logs.
Why this is correct
NCCL debug logs provide detailed information about the communication setup, including which transports are used, any fallbacks, and specific error codes. This is the most direct way to diagnose the cause of an 'unhandled system error', which can stem from hardware, driver, or configuration issues. Capturing logs during failure is the essential first step before attempting fixes.
Visual reference
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official NVIDIA exam blueprint
This NCP-AIO practice question is part of Courseiva's free NVIDIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NCP-AIO exam.