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NVIDIA Error 802 on Ubuntu: Diagnose Before Trying nokaslr

What a forum report about nokaslr actually establishes, and how to distinguish CUDA initialization and Fabric Manager failures.

2 min readflozi00
linuxsystemsnvidiadriversubuntuguide

The kernel parameter nokaslr disables kernel and module address randomization, as the Linux kernel documentation states. It has circulated as a workaround for some NVIDIA CUDA initialization failures. It is not a general fix for Ubuntu 24.04 black screens, driver installation failures or CUDA error 802. The previous version of this guide treated a forum user's proposed KASLR/CUDA-HMM explanation as a confirmed root cause; the cited discussion does not establish that.

What the case report actually shows

In an NVIDIA developer forum thread, a B200 user reported that nvidia-smi listed the GPUs while CUDA returned error 802. That user later attributed the issue to KASLR/CUDA HMM and proposed nokaslr. The forum response is a user report, not an NVIDIA engineering notice or a controlled diagnosis.

Crucially, another participant with error 802 said that disabling KASLR did not solve their case. They found that Fabric Manager could not load ib_umad; correcting the InfiniBand software setup resolved their problem. The same error code therefore does not identify KASLR as the cause. NVIDIA's Fabric Manager documentation is a better starting point on NVSwitch systems.

Check the failure stage

  1. If nvidia-smi fails, diagnose the host driver first using Ubuntu's driver guide. A black screen or missing kernel module has many possible causes and is not evidence for a KASLR conflict.
  2. If nvidia-smi works but CUDA fails on an NVSwitch system, inspect the Fabric Manager service and logs:
bash
systemctl status nvidia-fabricmanager
journalctl -u nvidia-fabricmanager -b
  1. Check whether driver and Fabric Manager versions match, and investigate any missing-module or NVSwitch errors in those logs. NVIDIA's GPUDirect Storage troubleshooting guide likewise points to matching Fabric Manager and driver versions for CUDA system-not-ready errors on NVSwitch systems.
  2. Only after another cause is excluded should nokaslr be considered as a temporary diagnostic experiment for a suspected kernel interaction. If it changes the result, record kernel, driver and hardware versions and report the finding to the vendor. A changed result alone does not prove the proposed CUDA-HMM mechanism.

Leaving nokaslr in the boot configuration disables a kernel exploit mitigation. Avoid making it a permanent default based solely on error 802. Re-test without it after driver or kernel updates and prefer a verified vendor fix when available.