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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.

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linuxsystemsnvidiadriversubuntuguide
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Locate the failed stage before changing a boot flag

Error 802 is a symptom; host-driver and NVSwitch initialization evidence determines the next diagnostic step.

AI-assisted learning visualization · schematic article explanation

Step 1 / 4Separate visibility from readiness

A GPU can appear in nvidia-smi while CUDA initialization still fails. Record the failing operation and exact versions so later changes can be compared.

WorkflowCurrent stepSelect a block to explain it
CUDA initialization fails
Record the exact error and hardware/software versions.
Does host nvidia-smi work?
GPU visibility and CUDA readiness are different checks.
  1. CUDA initialization fails Does host nvidia-smi work?
    first distinction
What to remember

Diagnose the failure stage and preserve evidence; error 802 does not by itself justify disabling KASLR.

This is a diagnostic map, not a confirmed KASLR/CUDA-HMM root cause. The cited forum workaround did not solve every case, and permanent nokaslr weakens a kernel mitigation.

Terms and the complete walkthrough
KASLR
Randomizing kernel address placement as an exploit mitigation.
Fabric Manager
NVIDIA software involved in initializing and managing supported NVSwitch fabrics.
Root cause
The demonstrated underlying reason for a failure, beyond its error message.
  1. Separate visibility from readiness

    A GPU can appear in nvidia-smi while CUDA initialization still fails. Record the failing operation and exact versions so later changes can be compared.

  2. Investigate the relevant layer

    If nvidia-smi fails, start with the host driver. On an NVSwitch system where it works but CUDA fails, inspect Fabric Manager logs, matching versions and missing modules.

  3. Use evidence to choose the next step

    The article’s forum cases had different outcomes and causes. Fix an identified problem; consider a temporary boot experiment only after other causes are excluded and a kernel interaction remains suspected.

  4. Preserve uncertainty and restore protection

    nokaslr turns off kernel and module address randomization. Even if the result changes, record the versions, restore normal protection and seek a verified fix; the change alone does not prove the proposed mechanism.

All connections

  • CUDA initialization fails → Does host nvidia-smi work?: first distinction
  • Does host nvidia-smi work? → Host driver diagnosis: does not work
  • Does host nvidia-smi work? → NVSwitch / Fabric Manager: works; NVSwitch present
  • Host driver diagnosis → Narrow the suspected cause: driver findings
  • NVSwitch / Fabric Manager → Narrow the suspected cause: service findings
  • Narrow the suspected cause → Conditional temporary experiment: suspected kernel interaction
  • Narrow the suspected cause → Record, restore and retest: verified cause found
  • Conditional temporary experiment → Record, restore and retest: record and restore
Set your own pace. Pause at any time or select a step directly.

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.