os and process

node:os exposes host capabilities; process exposes the current Node runtime - together they drive cluster sizing, health payloads, and environment configuration.

Recipe

import { availableParallelism, hostname, totalmem, freemem } from 'node:os';
 
console.log({
  host: hostname(),
  cpus: availableParallelism(),
  memFree: freemem(),
  memTotal: totalmem(),
  node: process.version,
  pid: process.pid,
});

When to reach for this:

• /health and /ready diagnostic payloads
• Sizing worker_threads pools and cluster forks
• Logging platform in structured startup banner
• Detecting container memory pressure before OOMKill

Working Example

import { availableParallelism, hostname, loadavg, platform, arch } from 'node:os';
 
export function hostSnapshot() {
  return {
    hostname: hostname(),
    platform: platform(),
    arch: arch(),
    nodeVersion: process.version,
    pid: process.pid,
    ppid: process.ppid,
    uptimeSec: process.uptime(),
    cpuParallelism: availableParallelism(),
    loadavg1m: loadavg()[0],
    memory: process.memoryUsage(),
    env: process.env.NODE_ENV ?? 'development',
  };
}
 
export function assertProductionEnv(): void {
  if (process.env.NODE_ENV === 'production' && !process.env.DATABASE_URL) {
    throw new Error('DATABASE_URL required in production');
  }
}

import { monitorEventLoopDelay } from 'node:perf_hooks';
 
const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();
 
setInterval(() => {
  console.log('eventLoopP99Ns', h.percentile(99), 'rss', process.memoryUsage().rss);
  h.reset();
}, 30_000).unref();

What this demonstrates:

• availableParallelism respects cgroup CPU limits in containers better than legacy cpus().length
• process.memoryUsage().rss tracks resident set - correlate with K8s OOM events
• loadavg Unix-specific - useful on Linux VMs, less on Windows
• Validate critical env at boot before accepting traffic

Deep Dive

How It Works

• process.env is mutable string map - copy at boot for immutability if desired.
• memoryUsage returns rss, heapTotal, heapUsed, external - not full process footprint but trendable.
• cpuUsage microsecond user/system time for current process.
• os.networkInterfaces lists NIC addresses - filter carefully before logging (PII/internal topology).

Useful Fields

TypeScript Notes

import { env } from 'node:process';
 
const nodeEnv = env.NODE_ENV ?? 'development';

Gotchas

• Logging full process.env - secrets leak. Fix: allowlist keys in health output.
• Using cpus().length in containers - wrong vCPU count. Fix: availableParallelism().
• Mutating process.env at runtime - subtle bugs in libraries. Fix: treat as immutable after bootstrap.
• Trusting hostname for security - spoofable context. Fix: authz not based on hostname alone.
• loadavg on Windows - returns zeros - do not rely cross-platform.

Alternatives

FAQs

Related

• Processes Basics - pid and workers
• Installing & Version Management - engines
• Detecting Event-Loop Blockage - perf_hooks
• Configuration Basics - env patterns

Stack versions: This page was written for Node.js 24.18.0 (Active LTS), npm 10+, TypeScript 5.6+, Express 5, Fastify 5, and NestJS 11.