Node-smoke test instruction

August 12, 2026 · View on GitHub

A lightweight, distributed-rendezvous-free preflight check that runs on every node in parallel under SLURM. It produces a single PASS/FAIL verdict per node plus SLURM-ready passing_nodes.txt / failing_nodes.txt you can pipe straight into srun --nodelist= / --exclude=.

Use it to screen a cluster fast and exclude bad nodes before launching a real training job. A bad GPU, NIC, wedged driver, or leaked process on any node surfaces as a node FAIL — without a single global rendezvous, so a stuck node can't wedge its peers.

Recommended launcher: runner/primus-cli slurm srun -- direct -- node_smoke ... (auto-resolves the distributed env, applies slurm.* config defaults, same pattern as train / benchmark). The shorter runner/primus-cli direct -- node_smoke ... (bare srun + direct) is equivalent and handy for ad-hoc runs.
Companion tool: preflight — the heavier diagnostic with a global rendezvous and inter-node bandwidth tests. The recommended workflow is node-smoke first, preflight second (see §10).

1. What it does

Node-smoke answers one question fast: "which nodes are healthy enough to run anything?" Because training jobs allocate whole nodes, a single degraded GPU (or NIC, or wedged driver) takes an entire node out of rotation. Node-smoke checks each node independently and emits a per-node verdict plus a ready-to-use exclude list, so you can prune broken nodes before committing a large job to a global rendezvous.

It deliberately does not measure cross-node bandwidth — that's what preflight is for.

2. How it works

Per-node and independent — every node runs the checks on its own. No MASTER_ADDR, no MASTER_PORT, no global torch.distributed rendezvous, so a stuck node cannot wedge its peers.
Per-GPU isolation — each GPU's checks run in their own Python subprocess with a hard timeout (--per-gpu-timeout-sec, default 15 s). A stuck torch.cuda.set_device() (which signal.alarm cannot interrupt because it sits inside a driver syscall) is SIGKILL'd from the parent without affecting the rest of the node's checks.
Local-only RCCL — the optional Tier 2 all-reduce uses torch.multiprocessing.spawn over tcp://127.0.0.1. No cross-node communication.
Rank-0 aggregation — NODE_RANK==0 polls for the expected number of per-node JSONs (with a timeout), computes cluster-wide drift, writes the Markdown report + pass/fail lists, and returns non-zero if any node FAILs or never reports.

3. Prerequisites

Prerequisite	How
Python venv on a shared filesystem	Same venv used by `primus-cli direct -- preflight` (see `preflight-without-container.md` §2).
`VENV_ACTIVATE` exported	`export VENV_ACTIVATE=~/envs/preflight/.venv/bin/activate` (optional inside the container path).
Inside an existing SLURM allocation	One task per node. Recommended: `runner/primus-cli slurm srun -N "$SLURM_NNODES" --ntasks-per-node=1 -- direct -- node_smoke ...`. Equivalent bare form: `srun ... --ntasks-per-node=1 runner/primus-cli direct -- node_smoke ...`. Either way the `direct -- node_smoke` path auto-selects `--single`, so each task spawns one Python process and per-GPU subprocesses are launched internally.

No MASTER_ADDR, no MASTER_PORT, no global rendezvous required.

4. Quick start

Git clone the Primus repository to a shared filesystem that all nodes can read.

git clone --recurse-submodules https://github.com/AMD-AGI/Primus.git
cd Primus

Note: remember to set up the Python virtual environment and NCCL / fabric environment variables as described in §3 Prerequisites.

⚠ Set the NCCL / RCCL environment first if you plan to run with --tier2-perf (the local 8-GPU RCCL all-reduce). Even though the smoke test never opens a cross-node rendezvous, the Tier 2 RCCL step calls dist.init_process_group(backend="nccl", ...), and RCCL enumerates every transport at init (XGMI / PCIe P2P + IB + sockets). A misconfigured NCCL_IB_HCA / NCCL_SOCKET_IFNAME / NCCL_IB_GID_INDEX can stall init or make the all-reduce silently fall back to a slow path. The launcher's base_env.sh auto-detects these, but auto-detect sometimes picks the wrong values inside a container (devices masked by the network namespace, frontend NICs picked up instead of fabric NICs, etc.), so check them and set them explicitly if auto-detection is wrong.

Minimum-viable checklist before running with --tier2-perf:
# Pin the RDMA / RoCE training NICs the container can actually see.
# On a bare-metal host the auto-detect in base_env.sh usually picks
# the right set; inside a container or on a multi-role node, list
# them explicitly. Use the same set you would pass to a training job.
export NCCL_IB_HCA="rdma0,rdma1,rdma2,rdma3,rdma4,rdma5,rdma6,rdma7"

# Pick the RoCE v2 GID index for your fabric:
#   - Mellanox / Broadcom: typically 3 (base_env.sh default).
#   - Pensando Pollara (AINIC): 1.
export NCCL_IB_GID_INDEX=3

# The bootstrap socket interface. Auto-detect prefers the first
# non-loopback interface from `hostname -I`; override when that
# picks a frontend NIC instead of the data-plane interface.
export NCCL_SOCKET_IFNAME=eno0
export GLOO_SOCKET_IFNAME=eno0
See preflight-without-container.md §4 Cluster-specific NCCL configuration for the canonical Broadcom / Pensando Pollara values (the same NCCL_* set is used by both tools). If you skip --tier2-perf, the RCCL step is not executed and none of the above applies — Tier 1 (host limits, RDMA roll-call, leaked-process detection, etc.) does not depend on RCCL.

Quick verification: runner/primus-cli direct --dry-run -- node_smoke --tier2-perf prints the resolved NCCL_* block under "Environment Variables" so you can confirm the values before launching for real.

Recommended — through the primus-cli slurm srun wrapper (auto-resolves MASTER_ADDR/NNODES/NODE_RANK, applies slurm.* config defaults):

export VENV_ACTIVATE=~/envs/preflight/.venv/bin/activate

# Basic Tier 1 check (~5 s/GPU, ~30 s total)
runner/primus-cli slurm srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    -- direct -- node_smoke

# Tier 1 + Tier 2 perf sanity (GEMM TFLOPS, HBM GB/s, local 8-GPU RCCL)
runner/primus-cli slurm srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    -- direct -- node_smoke --tier2-perf

# Then re-run training, excluding any node the smoke test failed:
srun --exclude=$(paste -sd, output/preflight/failing_nodes.txt) ... your-real-job

Equivalent with bare srun (works the same; useful when composing with custom srun flags):

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke --tier2-perf

Single-node sanity check (no SLURM):

runner/primus-cli direct -- node_smoke

Both forms produce the same workload. The wrapper form is recommended because it resolves the distributed env once on the launching node and propagates it via --env, and applies any slurm.* config defaults (partition / time / etc.). The direct keyword between the two --s is mandatory to take the no-container path — without it the wrapper routes through the container path. See preflight-without-container.md § Wrapper vs. bare-srun for the precedence table.

5. What's checked

A level='fail' finding in any check FAILs the node. Everything else is reported as info / warn.

Tier 1 — always runs (~5 s/GPU)

Per-GPU liveness (each GPU in its own subprocess with a hard timeout):

torch.cuda.set_device(i) — proves the device is bindable (a stale / wedged GPU often fails here).
256 MB allocation.
Tiny 2048² bf16 GEMM with an isfinite() check on the result.

Host / GPU / network inventory (no rendezvous):

dmesg recent-error scan — greps the last --dmesg-minutes (default 15) of dmesg for known patterns (xid, gpu reset, hung_task, mce:, amdgpu.*error, ...). Matches are surfaced in the report.
A. Software-stack fingerprint — kernel / OS / Python, ROCm version, amdgpu kernel-module version, PyTorch / torch.version.hip / RCCL versions, and per-IB-device firmware + HCA model. Used for cluster drift detection.
B. NIC / RDMA roll-call — per-port state read from /sys/class/infiniband (works inside containers; no ibv_devinfo / ibstat dependency). Many clusters expose more RDMA ports than the training job uses, so the hard-fail rules only run against the training-NIC subset, selected by this precedence:
1. --rdma-nic-allowlist (NCCL_IB_HCA syntax: comma-separated device[:port], ^... denylist, =dev exact-match).
2. NCCL_IB_HCA env (same syntax) — so the smoke test and the training launch agree by construction.
3. Heuristic: auto-exclude any port whose phys_state is Disabled or Sleep (admin-disabled).
4. Fallback: every IB port must be ACTIVE / LinkUp.
Hard-fail rules (on the included set only): port not ACTIVE / not LinkUp; active port with zero RoCE v2 GIDs (RoCE) or zero valid GIDs (IB); included-NIC count ≠ --expected-rdma-nics N (when set). If every discovered port gets excluded, the node still fails — a node with zero training NICs cannot participate in inter-node training. Excluded ports stay visible in the report for diagnostics but don't contribute to the FAIL signal.
C. Host limits / system tunables — RLIMIT_MEMLOCK below --ulimit-l-min-gb (default 32 GiB) → "RDMA pin will fail under load"; /dev/shm below --shm-min-gb (default 8 GiB) → "NCCL shared-mem may fail". NUMA node count, CPU count, and cpu0 scaling governor are collected for drift detection.
Foreign / leaked process detection — foreign PIDs holding a GPU FAIL the node by default (the most common cause of "training fails to launch on a healthy-looking node"). Allowed by default: gpuagent,rocm-smi-daemon,amd-smi,dcgm-exporter. See the container note in §6.5 — running inside a container almost always needs --allow-foreign-procs.
rocm-smi self-latency — a rocm-smi --version call slower than --rocm-smi-timeout-sec (default 5 s) is a node FAIL; a wedging amdgpu driver typically hangs rocm-smi for 30–60 s before the GPU itself stops responding.

Tier 2 — optional perf sanity (`--tier2-perf`)

Per-GPU steady-state metrics, with iteration counts aligned to the preflight --quick preset so smoke and preflight numbers are directly comparable. It's a single switch — you cannot enable just one half.

GEMM TFLOPS — 8192³ bf16 torch.matmul; FAIL below --gemm-tflops-min (default 600).
HBM GB/s — 512 MB device-to-device torch.Tensor.copy_ (counts read + write); FAIL below --hbm-gbs-min (default 2000; a healthy MI300X is ≈ 4500–5000).
Local 8-GPU RCCL all-reduce GB/s — algorithmic bandwidth 2·S·(P-1)/P / t / 1e9 at --rccl-size-mb (default 64 MB); FAIL below --rccl-gbs-min (default 100). Local only, no cross-node traffic.

6. Examples (by configuration knob)

Convention used below. The examples are written with bare srun for brevity. Anywhere you see srun <flags> runner/primus-cli direct -- node_smoke ..., the equivalent wrapper form is runner/primus-cli slurm srun <flags> -- direct -- node_smoke .... Pick whichever matches your habits; both target the same launcher.

6.1 Hard-fail on partial NIC enumeration

Catches "7 of 8 RDMA NICs visible" — a common cause of crashes after RoCE init. The count is compared against the training-NIC set (after the selector chain), so frontend / storage RoCE NICs do not inflate it.

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke --tier2-perf --expected-rdma-nics 8

6.2 Pin the training-NIC set explicitly

When auto-detection picks the wrong ports, name the training NICs directly (otherwise NCCL_IB_HCA env is used; otherwise admin-disabled ports are auto-excluded):

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke --tier2-perf \
    --rdma-nic-allowlist 'rocep158s0:1,rocep190s0:1,rocep206s0:1,rocep222s0:1,rocep28s0:1,rocep62s0:1,rocep79s0:1,rocep96s0:1'

6.3 Tighten Tier 2 perf thresholds

Reject GPUs that come in below your acceptance bar. Defaults: GEMM 600 TFLOPS, HBM 2000 GB/s, local RCCL 100 GB/s.

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke --tier2-perf \
        --gemm-tflops-min 700 --hbm-gbs-min 4500 --rccl-gbs-min 180

6.4 Tighten host limits

Fail nodes whose RLIMIT_MEMLOCK or /dev/shm is too small for production training.

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke \
        --ulimit-l-min-gb 64 --shm-min-gb 16

6.5 Allow / extend the foreign-process whitelist

By default, leaked / foreign processes holding a GPU FAIL the node. Allowed by default: gpuagent,rocm-smi-daemon,amd-smi,dcgm-exporter.

# Add a site-specific monitoring agent to the whitelist
srun ... runner/primus-cli direct -- node_smoke \
    --allowed-procs gpuagent,rocm-smi-daemon,amd-smi,dcgm-exporter,my-monitor

# Don't fail at all on foreign processes (still reported in the markdown)
srun ... runner/primus-cli direct -- node_smoke --allow-foreign-procs

⚠ Running node_smoke inside a container almost always trips this check. amd-smi process --json reports name="N/A" for kernel/system PIDs like gpuagent whose /proc/<host_pid>/comm it cannot read, and the fallback name resolution inside node_smoke also fails because the container's /proc typically does not expose host PIDs (private PID namespace without --pid=host, or a hidepid=2 mount). The unresolved name doesn't match the allowlist, so the check fires and the node FAILs — even though the only "foreign" processes are well-known system daemons holding zero HBM.

In the container path, pass --allow-foreign-procs:
srun ... runner/primus-cli direct -- node_smoke --tier2-perf --allow-foreign-procs
The processes are still listed in smoke_report.md under "Busy GPUs / leaked processes", so a real leak is still visible; only the FAIL verdict is downgraded.

Narrower alternative — add the literal sentinel N/A to the allowlist so the check still catches leaks with resolvable names (e.g. a leftover python rank):
srun ... runner/primus-cli direct -- node_smoke --tier2-perf \
    --allowed-procs gpuagent,rocm-smi-daemon,amd-smi,dcgm-exporter,N/A
Name resolution runs first, so whenever a real name can be resolved it overrides N/A and the normal allowlist applies — the N/A entry only matches PIDs whose name genuinely could not be recovered.

Root-cause fix (preferred long-term): grant the container access to host PIDs so names resolve and the report shows gpuagent etc. instead of N/A. Typical fixes: launch with --pid=host (Docker / Podman); mount /proc without hidepid=2; or loosen ptrace_scope / grant CAP_SYS_PTRACE.

6.6 Require specific tools

Make missing CLI tools a hard FAIL (default: warn-only).

srun ... runner/primus-cli direct -- node_smoke --require-tools amd-smi,rocm-smi,lsof

6.7 Skip dmesg scan (containers with no privileges)

srun ... runner/primus-cli direct -- node_smoke --skip-dmesg

6.8 Custom dump path

Keep one report per smoke run instead of overwriting the default location.

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct -- node_smoke --tier2-perf \
        --dump-path /shared/smoke-archive/$(date +%Y%m%d-%H%M%S)

6.9 Re-aggregate from existing per-node JSONs (no re-run)

The primus-cli wrapper always runs both phases (per-node run + rank-0 aggregate). To only re-render the report from JSONs collected earlier, use the standalone aggregate subcommand — it reads the existing <dump>/smoke/*.json without re-running the per-node step:

python -m primus.tools.preflight.node_smoke aggregate \
    --dump-path output/preflight --expected-nodes 6 --wait-timeout-sec 5

6.10 Silent mode (for CI)

Suppresses wrapper stdout, but the final report path is still printed and stderr / exit code are preserved.

srun ... runner/primus-cli direct --silent -- node_smoke --tier2-perf

6.11 Combined "production-ready screen"

A representative one-shot for a production cluster screen:

srun -N "$SLURM_NNODES" --ntasks-per-node=1 \
    runner/primus-cli direct --silent -- node_smoke --tier2-perf \
        --expected-rdma-nics 8 \
        --gemm-tflops-min 700 --hbm-gbs-min 4500 --rccl-gbs-min 180 \
        --ulimit-l-min-gb 64 --shm-min-gb 16 \
        --require-tools amd-smi,rocm-smi,lsof \
        --dump-path /shared/smoke-archive/$(date +%Y%m%d-%H%M%S)

7. Outputs

All written under --dump-path (default output/preflight/).

File	Purpose
`smoke/<short-host>.json`	Per-node verdict + every collected metric. One file per node.
`smoke_report.md`	Human-readable cluster report (status table, drift sections, perf summary, failing-node detail).
`passing_nodes.txt`	Newline-separated short hostnames. Pipe into `srun --nodelist=`.
`failing_nodes.txt`	Newline-separated short hostnames. Pipe into `srun --exclude=`.
`expected_nodes.txt`	Auto-populated from `scontrol show hostnames "$SLURM_JOB_NODELIST"`. Lets the report name nodes that never reported.

Read the cluster verdict at a glance:

head -10 output/preflight/smoke_report.md

Feed bad nodes into a re-run:

srun --exclude=$(paste -sd, output/preflight/failing_nodes.txt) ... your-real-job

8. Understanding the report

smoke_report.md renders in a stable order. Each section short-circuits to a placeholder (e.g. *All nodes match.*, *No NIC issues.*) on a healthy cluster, so a clean report stays short. In order:

Status table — one row per node: node_rank, hostname, PASS/FAIL, duration, top fail reason.
Stack drift across cluster — per fingerprint key, outliers vs the cluster majority (catches "1 of N nodes on a different RCCL build").
NIC firmware drift across cluster — per-IB-device firmware drift.
NIC / RDMA roll-call issues — every offending node + port (included set only).
NIC port-count summary — cluster-majority training-NIC count and any node that disagrees (catches partial-NIC degradation even without --expected-rdma-nics).
NIC excluded ports (informational) — ports the selector chain dropped, grouped by source. Does not contribute to FAIL.
Host limits issues — per-node hard-limit violations.
GPU visibility issues — nodes where torch couldn't see the GPUs, or amd-smi sees more GPUs than torch (stale ROCm / wedged driver).
GPU low-level outliers (PCIe link / HBM) — per-GPU outliers vs the cluster majority on PCIe width/speed and HBM total.
XGMI link issues — any non-XGMI GPU pair (intra-node collectives silently fall back to PCIe).
Cluster clock + time daemons — wall-clock spread plus per-node time-daemon health.
Tooling self-latency (rocm-smi --version) — slow / timed-out tool calls (precursor to a wedged driver).
Tooling availability — inventory of amd-smi / rocm-smi / lsof per node, plus which Tier 1 checks have no working tool on each node.
Busy GPUs / leaked processes — foreign PIDs holding GPUs at smoke start.
GPU pre-touch HBM usage outliers — GPUs with non-trivial HBM in use before smoke touched the device.
GPU compute-activity outliers — GPUs above --gpu-activity-warn-pct at smoke start (warn-only).
Tier 2 perf summary (only when at least one node ran Tier 2) — per-node GEMM TFLOPS / HBM GB/s as min / median / max, plus local RCCL GB/s.
Failing nodes — full reasons (only when there are failing nodes) — every fail reason, expanded per node.

9. Configuration reference

9.1 Common knobs (cheat sheet)

Flag	Default	When you'd change it
`--tier2-perf`	off	Always on for production screens — adds GEMM TFLOPS, HBM GB/s, local RCCL all-reduce.
`--gemm-tflops-min N`	600	Site-specific acceptance bar.
`--hbm-gbs-min N`	2000	Site-specific acceptance bar (MI300X healthy ≈ 4500–5000).
`--rccl-gbs-min N`	100	Site-specific acceptance bar.
`--expected-rdma-nics N`	unset	Hard-fail on partial NIC enumeration.
`--ulimit-l-min-gb GB`	32	Raise for production training profiles.
`--shm-min-gb GB`	8	Raise for large-batch / many-rank profiles.
`--allow-foreign-procs`	off	Co-tenant clusters, shared GPUs, or the container path (see §6.5).
`--allowed-procs LIST`	`gpuagent,rocm-smi-daemon,amd-smi,dcgm-exporter`	Add site-specific monitoring agents.
`--require-tools LIST`	`""`	Fail-fast if a CLI tool is missing in PATH.
`--skip-dmesg`	off	Inside unprivileged containers.
`--dump-path DIR`	`output/preflight`	Archive each run separately.
`--silent` (launcher)	off	CI / scripted runs.

9.2 Full `node_smoke` (per-node) flags

Authoritative source: python -m primus.tools.preflight.node_smoke run --help.

Flag	Default	Purpose
`--dump-path`	`output/preflight`	Output directory.
`--expected-gpus N`	auto	Override GPU count (auto-detected from `LOCAL_WORLD_SIZE` / `GPUS_PER_NODE` / `torch.cuda.device_count()`).
`--per-gpu-timeout-sec`	15	Hard timeout per per-GPU subprocess.
`--tier2-perf`	off	Enable Tier 2 perf sanity (per-GPU GEMM TFLOPS + HBM GB/s + node-local RCCL all-reduce). Single switch.
`--gemm-tflops-min`	600	Tier 2 GEMM threshold.
`--hbm-gbs-min`	2000	Tier 2 HBM threshold.
`--rccl-size-mb`	64	Local RCCL message size.
`--rccl-gbs-min`	100	Local RCCL bandwidth threshold.
`--rccl-timeout-sec`	120	Hard timeout for the RCCL phase.
`--skip-dmesg`	off	Skip dmesg scan (e.g. inside containers).
`--dmesg-minutes`	15	dmesg `--since` window.
`--expected-rdma-nics N`	auto (report-only)	When set, a mismatch between the included (training-NIC) count and N becomes a node FAIL.
`--rdma-nic-allowlist LIST`	unset	Explicit training-NIC selector in `NCCL_IB_HCA` syntax (`device[:port],...`, `^...` denylist, `=dev` exact-match). Wins over `NCCL_IB_HCA` env. When neither is set, ports whose `phys_state` is `Disabled` / `Sleep` are auto-excluded.
`--ulimit-l-min-gb GB`	32	`RLIMIT_MEMLOCK` threshold (0 disables).
`--shm-min-gb GB`	8	`/dev/shm` size threshold (0 disables).
`--rocm-smi-timeout-sec SEC`	5.0	Hard timeout for the `rocm-smi --version` self-latency canary; hitting it is a node FAIL.
`--hbm-busy-threshold-gib GiB`	2.0	FAIL if any GPU has ≥ this much HBM in use before smoke touches the device. Boundary inclusive.
`--allow-foreign-procs`	off	Do NOT FAIL on foreign processes holding a GPU. They are still reported.
`--allowed-procs LIST`	`gpuagent,rocm-smi-daemon,amd-smi,dcgm-exporter`	Process names OK to find holding the GPU. Set to `""` to disable the whitelist.
`--gpu-activity-warn-pct PCT`	20.0	Warn (does NOT fail) if any GPU's `gfx_activity_pct` exceeds this at smoke start.
`--require-tools LIST`	`""` (warn-only)	CLI tools that MUST be in PATH (`amd-smi`, `rocm-smi`, `lsof`); anything missing becomes a hard node FAIL.
`--no-clean-dump-path`	off	Do NOT auto-wipe stale per-node JSONs / aggregator outputs from `--dump-path` on rank 0 at startup.

9.3 Standalone `aggregate` flags

The primus-cli wrapper runs the aggregator automatically on rank 0 and fills --expected-nodes / --expected-nodelist-file from SLURM. These matter only when you invoke python -m primus.tools.preflight.node_smoke aggregate yourself (see §6.9).

Flag	Default	Purpose
`--dump-path`	`output/preflight`	Same as `run`.
`--expected-nodes N`	none	If fewer JSONs land within `--wait-timeout-sec`, missing nodes are added as FAIL placeholders.
`--wait-timeout-sec`	60	Polling timeout.
`--rocm-smi-warn-sec SEC`	1.0	Flag (warn-only) any node where `rocm-smi --version` took longer than this.
`--clock-skew-warn-sec SEC`	30.0	Warn when wall-clock spread across nodes exceeds this many seconds (includes srun launch jitter).
`--hbm-busy-threshold-gib GiB`	2.0	Mirrors the `run` default; labels the "GPU pre-touch HBM usage outliers" section.
`--gpu-activity-warn-pct PCT`	20.0	Mirrors the `run` default; labels the "GPU compute-activity outliers" section.
`--expected-nodelist-file FILE`	none	One short hostname per line. Missing nodes get their real short hostname in the report and `failing_nodes.txt`. The wrapper auto-populates this from `scontrol show hostnames "$SLURM_JOB_NODELIST"` under SLURM.

9.4 Launcher-level knobs (`primus-cli direct`)

Consumed by primus-cli-direct.sh before the -- separator (not forwarded to the node_smoke Python tool):

Flag	Purpose
`--silent`	Redirect launcher + tool stdout to `/dev/null`. Launcher errors (`LOG_ERROR` / `LOG_WARN` on stderr) and the log file are preserved. Exit code propagated.
`--debug`	Verbose launcher logging.
`--dry-run`	Print the resolved configuration and command without executing.
`--env KEY=VALUE`	Inject an env var into the Python process.

Run vs. aggregate. The primus-cli node_smoke subcommand always runs the per-node checks on every rank, then aggregates on rank 0 — which is what you want ~100% of the time, so there is no --aggregate-only wrapper flag. For the rare single-phase cases, call the standalone CLI directly: python -m primus.tools.preflight.node_smoke run ... (per-node only, no report) or ... aggregate ... (report only, from existing JSONs).

10. Comparison with the full `preflight`

Aspect	`node_smoke`	full `preflight`
Rendezvous	None — every node independent	Global `torch.distributed`
Wall clock	~30–60 s for 6 nodes (Tier 1+2)	Minutes; scales with N for inter-node tests
Granularity	Per-node PASS/FAIL	Per-rank measurements (no auto-fail by default)
GEMM	Hard threshold per GPU	Reports per-GPU numbers, no auto-fail
HBM bandwidth	Yes (D2D `copy_`)	Not measured
Inter-node all-reduce / all-to-all	Not tested (intentionally)	Yes
Drift detection	Yes (versions, NIC firmware, port count)	No
Host limits / RDMA roll-call	Yes (hard fail)	Reported via `collect_*_info` only
Output format	Per-node JSON + cluster md + SLURM-ready txt	Markdown + PDF

Use node_smoke to screen a cluster fast and exclude bad nodes. Use the full preflight when you want deep cross-node measurements (inter-node bandwidth matrix, ring-P2P, etc.). The recommended sequence is node-smoke first, then preflight --quick on the surviving nodes.

11. Troubleshooting

Symptom	Likely cause / fix
`[ERROR] [direct] VENV_ACTIVATE is set but file does not exist: ...`	Fix the path (`export VENV_ACTIVATE=~/envs/preflight/.venv/bin/activate`), or `unset VENV_ACTIVATE` to fall back to system / container Python.
Every node FAILs with `gpu_processes: ... name='N/A'`	Container `/proc` can't resolve host PID names. See §6.5: pass `--allow-foreign-procs`, or grant host-PID visibility.
Some nodes never produce a JSON	The aggregator names them in `failing_nodes.txt` via `expected_nodes.txt`. If `scontrol` was unavailable, they appear as `<missing-N>`.
Tier 2 perf numbers below threshold on a known-good node	Almost always insufficient CPU cores on `srun` — pass `-c <cores-per-node>` so RCCL proxy threads have CPU.
Re-run on a smaller nodelist still shows the previously removed nodes as PASS	Default behavior cleans stale JSONs on rank 0. If you passed `--no-clean-dump-path`, either remove it or `rm -rf output/preflight` between runs.

12. See also

preflight.md — the heavier preflight tool with a global rendezvous and inter-node bandwidth tests.
preflight-without-container.md — running preflight directly on the host (no container), including the shared venv + NCCL setup.
primus/cli/subcommands/node_smoke.py — the primus-cli subcommand wiring (two-phase dispatch: per-rank run + rank-0 aggregate).
primus/tools/preflight/node_smoke/cli.py — canonical flag definitions and per-node / aggregate phase bodies.