Node.js OS Module
What is the OS Module?
The OS module in Node.js provides a powerful set of utilities for interacting with the underlying operating system.
It offers a cross-platform way to access system-related information and perform common operating system tasks.Key Features:
- Retrieve system information (CPU, memory, platform, etc.)
- Access user and network information
- Work with file paths and directories in a cross-platform way
- Monitor system resources and performance
- Handle operating system signals and errors
Getting Started with the OS Module
Importing the Module
The OS module is a core Node.js module, so no installation is needed.
You can import it using CommonJS or ES modules syntax:
CommonJS (default in Node.js)
const os = require('os');
ES Modules (Node.js 14+ or with "type": "module" in package.json)
import os from 'os';
// or
import { arch, platform, cpus } from 'os';
Basic Usage Example
Here's a quick example showing some common OS module methods:
const os = require('os');
// Basic system information
console.log(`OS Platform: ${os.platform()}`);
console.log(`OS Type: ${os.type()}`);
console.log(`OS Release: ${os.release()}`);
console.log(`CPU Architecture: ${os.arch()}`);
console.log(`Hostname: ${os.hostname()}`);
// Memory information
const totalMemGB = (os.totalmem() / (1024 * 1024 * 1024)).toFixed(2);
const freeMemGB = (os.freemem() / (1024 * 1024 * 1024)).toFixed(2);
console.log(`Memory: ${freeMemGB}GB free of ${totalMemGB}GB`);
// User information
const userInfo = os.userInfo();
console.log(`Current User: ${userInfo.username}`);
console.log(`Home Directory: ${os.homedir()}`);
Try it Yourself »
OS Module Reference
Note: All OS module methods are synchronous and return results immediately.
For performance-critical applications, consider caching the results of methods that might be called frequently, such as os.cpus() or os.networkInterfaces().
System Information
os.arch()
Returns the operating system CPU architecture for which the Node.js binary was compiled.
const os = require('os');
// Get CPU architecture
console.log(`CPU Architecture: ${os.arch()}`);
// Common values:
// - 'x64' for 64-bit systems
// - 'arm' for ARM processors
// - 'arm64' for 64-bit ARM
// - 'ia32' for 32-bit x86
// - 'mips' for MIPS processors
Try it Yourlself »
os.platform()
Returns a string identifying the operating system platform.
const os = require('os');
// Get platform information
const platform = os.platform();
console.log(`Platform: ${platform}`);
// Common values:
// - 'darwin' for macOS
// - 'win32' for Windows (both 32-bit and 64-bit)
// - 'linux' for Linux
// - 'freebsd' for FreeBSD
// - 'openbsd' for OpenBSD
Try it Yourself »
os.type()
Returns the operating system name as returned by uname on POSIX systems, or from the ver command on Windows.
const os = require('os');
// Get OS type
console.log(`OS Type: ${os.type()}`);
// Examples:
// - 'Linux' on Linux
// - 'Darwin' on macOS
// - 'Windows_NT' on Windows
Try it Yourself »
os.release()
Returns the operating system release number.
const os = require('os');
// Get OS release information
console.log(`OS Release: ${os.release()}`);
// Examples:
// - '10.0.19044' on Windows 10
// - '21.6.0' on macOS Monterey
// - '5.15.0-46-generic' on Ubuntu
Try it Yourself »
os.version()
Returns a string identifying the kernel version. On Windows, this includes build information.
const os = require('os');
// Get kernel version
console.log(`Kernel Version: ${os.version()}`);
// Example output:
// - Windows: 'Windows 10 Enterprise 10.0.19044'
// - Linux: '#49-Ubuntu SMP Tue Aug 2 08:49:28 UTC 2022'
// - macOS: 'Darwin Kernel Version 21.6.0: ...'
User and Environment
os.userInfo()
Returns information about the currently effective user.
const os = require('os');
// Get current user information
const user = os.userInfo();
console.log('User Information:');
console.log(`- Username: ${user.username}`);
console.log(`- User ID: ${user.uid}`);
console.log(`- Group ID: ${user.gid}`);
console.log(`- Home Directory: ${user.homedir}`);
// On Windows, you can also get the user's domain
if (os.platform() === 'win32') {
console.log(`- Domain: ${user.domain || 'N/A'}`);
}
// Note: user.shell is only available on POSIX platforms
if (user.shell) {
console.log(`- Default Shell: ${user.shell}`);
}
Run Example »
os.homedir()
Returns the home directory of the current user.
const os = require('os');
const path = require('path');
// Get the home directory
const homeDir = os.homedir();
console.log(`Home Directory: ${homeDir}`);
// Example: Create a path to a config file in the user's home directory
const configPath = path.join(homeDir, '.myapp', 'config.json');
console.log(`Config file will be saved to: ${configPath}`);
Try it Yourself »
os.hostname()
Returns the hostname of the operating system.
const os = require('os');
// Get the system hostname
const hostname = os.hostname();
console.log(`Hostname: ${hostname}`);
// Example: Use hostname in logging or configuration
console.log(`Server started on ${hostname} at ${new Date().toISOString()}`);
Try it Yourself »
os.tmpdir()
Returns the operating system's default directory for temporary files.
const os = require('os');
// Get the system default temp dir
console.log(`Temporary Directory: ${os.tmpdir()}`);
Try it Yourself »
System Resources
os.cpus()
Returns an array of objects containing information about each logical CPU core.
const os = require('os');
// Get CPU information
const cpus = os.cpus();
console.log(`Number of CPU Cores: ${cpus.length}`);
// Display information about each CPU core
cpus.forEach((cpu, index) => {
console.log(`\nCPU Core ${index + 1}:`);
console.log(`- Model: ${cpu.model}`);
console.log(`- Speed: ${cpu.speed} MHz`);
console.log('- Times (ms):', {
user: cpu.times.user,
nice: cpu.times.nice,
sys: cpu.times.sys,
idle: cpu.times.idle,
irq: cpu.times.irq
});
});
// Calculate total CPU usage (example, requires two measurements)
function calculateCpuUsage(prevCpus) {
const currentCpus = os.cpus();
const usage = [];
for (let i = 0; i < currentCpus.length; i++) {
const current = currentCpus[i];
const prev = prevCpus ? prevCpus[i] : { times: { user: 0, nice: 0, sys: 0, idle: 0, irq: 0 } };
const prevIdle = prev.times.idle;
const idle = current.times.idle - prevIdle;
let total = 0;
for (const type in current.times) {
total += current.times[type] - (prev.times[type] || 0);
}
const usagePercent = ((1 - idle / total) * 100).toFixed(1);
usage.push(parseFloat(usagePercent));
}
return {
perCore: usage,
average: (usage.reduce((a, b) => a + b, 0) / usage.length).toFixed(1),
cpus: currentCpus
};
}
// Example usage of CPU usage calculation
console.log('\nCPU Usage (requires two measurements):');
const firstMeasure = os.cpus();
// Simulate some CPU work
for (let i = 0; i < 1000000000; i++) {}
const usage = calculateCpuUsage(firstMeasure);
console.log(`Average CPU Usage: ${usage.average}%`);
Try it Yourself »
os.totalmem() and os.freemem()
Return the total and free system memory in bytes, respectively.
const os = require('os');
// Format bytes to human-readable format
function formatBytes(bytes, decimals = 2) {
if (bytes === 0) return '0 Bytes';
const k = 1024;
const dm = decimals < 0 ? 0 : decimals;
const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
const i = Math.floor(Math.log(bytes) / Math.log(k));
return parseFloat((bytes / Math.pow(k, i)).toFixed(dm)) + ' ' + sizes[i];
}
// Get memory information
const totalMem = os.totalmem();
const freeMem = os.freemem();
const usedMem = totalMem - freeMem;
const usagePercent = ((usedMem / totalMem) * 100).toFixed(2);
console.log('Memory Information:');
console.log(`- Total Memory: ${formatBytes(totalMem)}`);
console.log(`- Free Memory: ${formatBytes(freeMem)} (${((freeMem / totalMem) * 100).toFixed(2)}%)`);
console.log(`- Used Memory: ${formatBytes(usedMem)} (${usagePercent}%)`);
// Example: Check if there's enough free memory
const MIN_FREE_MEMORY = 200 * 1024 * 1024; // 200MB
if (freeMem < MIN_FREE_MEMORY) {
console.warn('Warning: Low on memory!');
} else {
console.log('System has sufficient memory available');
}
Try it Yourself »
os.loadavg()
Returns an array containing the 1, 5, and 15 minute load averages.
const os = require('os');
// Get load averages
const loadAverages = os.loadavg();
console.log('System Load Averages (1, 5, 15 min):', loadAverages);
// On Linux/Unix, load average represents the average system load over the last 1, 5, and 15 minutes
// The values represent the number of processes in the system run queue
const [oneMin, fiveMin, fifteenMin] = loadAverages;
const cpuCount = os.cpus().length;
console.log(`1-minute load average: ${oneMin.toFixed(2)} (${(oneMin / cpuCount * 100).toFixed(1)}% of ${cpuCount} cores)`);
console.log(`5-minute load average: ${fiveMin.toFixed(2)}`);
console.log(`15-minute load average: ${fifteenMin.toFixed(2)}`);
// Example: Check if system is under heavy load
const isSystemOverloaded = oneMin > cpuCount * 1.5;
if (isSystemOverloaded) {
console.warn('Warning: System is under heavy load!');
} else {
console.log('System load is normal');
}
Try it Yourself »
Network Information
os.networkInterfaces()
Returns an object containing network interfaces that have been assigned a network address.
const os = require('os');
// Get network interfaces information
const networkInterfaces = os.networkInterfaces();
console.log('Network Interfaces:');
// Iterate over each network interface
Object.entries(networkInterfaces).forEach(([name, addresses]) => {
console.log(`\nInterface: ${name}`);
addresses.forEach((address) => {
console.log(`- Family: ${address.family}`);
console.log(` Address: ${address.address}`);
console.log(` Netmask: ${address.netmask}`);
console.log(` MAC: ${address.mac || 'N/A'}`);
console.log(` Internal: ${address.internal}`);
});
});
// Example: Find the first non-internal IPv4 address
function getLocalIpAddress() {
const interfaces = os.networkInterfaces();
for (const name of Object.keys(interfaces)) {
for (const iface of interfaces[name]) {
if (iface.family === 'IPv4' && !iface.internal) {
return iface.address;
}
}
}
return '127.0.0.1'; // Fallback to localhost
}
const localIp = getLocalIpAddress();
console.log(`\nLocal IP Address: ${localIp}`);
Try it Yourself »
os.uptime()
Returns the system uptime in seconds.
const os = require('os');
// Get system uptime in seconds
const uptime = os.uptime();
console.log(`System Uptime: ${uptime} seconds`);
// Format uptime in a more readable way
const uptimeDays = Math.floor(uptime / (60 * 60 * 24));
const uptimeHours = Math.floor((uptime % (60 * 60 * 24)) / (60 * 60));
const uptimeMinutes = Math.floor((uptime % (60 * 60)) / 60);
const uptimeSeconds = Math.floor(uptime % 60);
console.log(`System has been running for: ${uptimeDays} days, ${uptimeHours} hours, ${uptimeMinutes} minutes, ${uptimeSeconds} seconds`);
Try it Yourself »
os.networkInterfaces()
Returns an object containing information about network interfaces.
const os = require('os');
// Get network interfaces
const networkInterfaces = os.networkInterfaces();
console.log('Network Interfaces:');
console.log(JSON.stringify(networkInterfaces, null, 2));
// Iterate through network interfaces
Object.keys(networkInterfaces).forEach((interfaceName) => {
console.log(`\nInterface: ${interfaceName}`);
networkInterfaces[interfaceName].forEach((interface) => {
console.log(` Address Family: ${interface.family}`);
console.log(` IP Address: ${interface.address}`);
console.log(` Netmask: ${interface.netmask}`);
if (interface.mac) {
console.log(` MAC Address: ${interface.mac}`);
}
console.log(` Internal: ${interface.internal ? 'Yes' : 'No'}`);
});
});
// Function to get primary IPv4 address (non-internal)
function getPrimaryIPv4Address() {
const interfaces = os.networkInterfaces();
for (const name of Object.keys(interfaces)) {
for (const interface of interfaces[name]) {
// Skip internal and non-IPv4 addresses
if (!interface.internal && interface.family === 'IPv4') {
return interface.address;
}
}
}
return 'No IPv4 address found';
}
console.log(`\nPrimary IPv4 Address: ${getPrimaryIPv4Address()}`);
Try it Yourself »
OS Constants and Utilities
os.constants
Returns an object containing commonly used operating system specific constants for error codes, process signals, and more.
const os = require('os');
// Get all signal constants
console.log('Signal Constants:', os.constants.signals);
// Example: Handle common signals
process.on('SIGINT', () => {
console.log('Received SIGINT. Performing cleanup...');
process.exit(0);
});
process.on('SIGTERM', () => {
console.log('Received SIGTERM. Shutting down gracefully...');
process.exit(0);
});
console.log('Process is running. Press Ctrl+C to exit.');
Try it Yourself »
os.EOL
Returns the end-of-line marker for the current operating system.
const os = require('os');
const fs = require('fs');
// Get the end-of-line marker for the current OS
console.log('End of Line character:', JSON.stringify(os.EOL));
// Example: Write a file with platform-specific line endings
const lines = [
'First line',
'Second line',
'Third line'
];
// Join lines with the correct EOL character
const content = lines.join(os.EOL);
fs.writeFileSync('output.txt', content);
console.log('File written with platform-appropriate line endings');
Try it Yourself »
Best Practices
1. Handle Paths Correctly
Always use path.join() instead of string concatenation for file paths to ensure cross-platform compatibility.
// Good
const filePath = path.join(os.homedir(), 'app', 'config.json');
// Bad (won't work on Windows)
const badPath = `${os.homedir()}/app/config.json`;
2. Be Cautious with os.EOL
When writing files, be aware of line endings. Use os.EOL for cross-platform compatibility.
const content = `First Line${os.EOL}Second Line${os.EOL}Third Line`;
fs.writeFileSync('output.txt', content, 'utf8');
3. Handle Memory Constraints
Check available memory before performing memory-intensive operations.
const MIN_FREE_MEMORY_MB = 500; // 500MB minimum free memory
function canPerformMemoryIntensiveOperation() {
const freeMemMB = os.freemem() / (1024 * 1024);
return freeMemMB > MIN_FREE_MEMORY_MB;
}
if (!canPerformMemoryIntensiveOperation()) {
console.warn('Not enough free memory to perform this operation');
// Handle the error appropriately
}
Practical Examples
System Information Dashboard
This example creates a comprehensive system information report:
const os = require('os');
function getSystemInfo() {
const info = {
os: {
type: os.type(),
platform: os.platform(),
architecture: os.arch(),
release: os.release(),
hostname: os.hostname(),
uptime: formatUptime(os.uptime())
},
user: {
username: os.userInfo().username,
homedir: os.homedir(),
tempdir: os.tmpdir()
},
memory: {
total: formatBytes(os.totalmem()),
free: formatBytes(os.freemem()),
usage: `${((1 - os.freemem() / os.totalmem()) * 100).toFixed(2)}%`
},
cpu: {
model: os.cpus()[0].model,
cores: os.cpus().length,
speed: `${os.cpus()[0].speed} MHz`
}
};
return info;
}
function formatUptime(seconds) {
const days = Math.floor(seconds / (60 * 60 * 24));
const hours = Math.floor((seconds % (60 * 60 * 24)) / (60 * 60));
const minutes = Math.floor((seconds % (60 * 60)) / 60);
const secs = Math.floor(seconds % 60);
return `${days}d ${hours}h ${minutes}m ${secs}s`;
}
function formatBytes(bytes) {
const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
if (bytes === 0) return '0 Bytes';
const i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
return `${(bytes / Math.pow(1024, i)).toFixed(2)} ${sizes[i]}`;
}
// Display the system information dashboard
const systemInfo = getSystemInfo();
console.log('======= SYSTEM INFORMATION DASHBOARD =======');
console.log(JSON.stringify(systemInfo, null, 2));
// Display in a more formatted way
console.log('\n======= FORMATTED SYSTEM INFORMATION =======');
console.log(`OS: ${systemInfo.os.type} (${systemInfo.os.platform} ${systemInfo.os.architecture})`);
console.log(`Version: ${systemInfo.os.release}`);
console.log(`Hostname: ${systemInfo.os.hostname}`);
console.log(`Uptime: ${systemInfo.os.uptime}`);
console.log(`User: ${systemInfo.user.username}`);
console.log(`Home Directory: ${systemInfo.user.homedir}`);
console.log(`CPU: ${systemInfo.cpu.model}`);
console.log(`Cores: ${systemInfo.cpu.cores}`);
console.log(`Speed: ${systemInfo.cpu.speed}`);
console.log(`Memory Total: ${systemInfo.memory.total}`);
console.log(`Memory Free: ${systemInfo.memory.free}`);
console.log(`Memory Usage: ${systemInfo.memory.usage}`);
Run Example »
Resource Monitor
This example creates a basic resource monitor that updates every second:
const os = require('os');
function monitorResources() {
console.clear(); // Clear console for a cleaner display
const now = new Date().toLocaleTimeString();
console.log(`======= RESOURCE MONITOR (${now}) =======`);
// CPU Usage
const cpus = os.cpus();
console.log(`\nCPU Cores: ${cpus.length}`);
// Calculate CPU usage (this is approximate since we need two measurements)
const cpuUsage = cpus.map((cpu, index) => {
const total = Object.values(cpu.times).reduce((acc, tv) => acc + tv, 0);
const idle = cpu.times.idle;
const usage = ((total - idle) / total * 100).toFixed(1);
return `Core ${index}: ${usage}% used`;
});
console.log(cpuUsage.join('\n'));
// Memory Usage
const totalMem = os.totalmem();
const freeMem = os.freemem();
const usedMem = totalMem - freeMem;
console.log('\nMemory Usage:');
console.log(`Total: ${formatBytes(totalMem)}`);
console.log(`Used: ${formatBytes(usedMem)} (${(usedMem / totalMem * 100).toFixed(1)}%)`);
console.log(`Free: ${formatBytes(freeMem)} (${(freeMem / totalMem * 100).toFixed(1)}%)`);
// System Uptime
console.log(`\nSystem Uptime: ${formatUptime(os.uptime())}`);
// Process Info
console.log('\nProcess Information:');
console.log(`PID: ${process.pid}`);
console.log(`Memory Usage: ${formatBytes(process.memoryUsage().rss)}`);
console.log(`User: ${os.userInfo().username}`);
}
function formatBytes(bytes) {
const sizes = ['Bytes', 'KB', 'MB', 'GB', 'TB'];
if (bytes === 0) return '0 Bytes';
const i = parseInt(Math.floor(Math.log(bytes) / Math.log(1024)));
return `${(bytes / Math.pow(1024, i)).toFixed(2)} ${sizes[i]}`;
}
function formatUptime(seconds) {
const days = Math.floor(seconds / (60 * 60 * 24));
const hours = Math.floor((seconds % (60 * 60 * 24)) / (60 * 60));
const minutes = Math.floor((seconds % (60 * 60)) / 60);
const secs = Math.floor(seconds % 60);
return `${days}d ${hours}h ${minutes}m ${secs}s`;
}
// Initial display
monitorResources();
// Update every second (note: in a real application, you might not want
// to update this frequently as it uses CPU resources)
const intervalId = setInterval(monitorResources, 1000);
// In a real application, you would need to handle cleanup:
// clearInterval(intervalId);
// For this example, we'll run for 10 seconds then stop
console.log('Monitor will run for 10 seconds...');
setTimeout(() => {
clearInterval(intervalId);
console.log('\nResource monitoring stopped.');
}, 10000);
Run Example »
Platform-Specific Behavior
This example demonstrates how to adapt your application's behavior based on the operating system:
const os = require('os');
const fs = require('fs');
const path = require('path');
// Function to determine a good location for app data based on the OS
function getAppDataPath(appName) {
const platform = os.platform();
let appDataPath;
switch (platform) {
case 'win32': // Windows
appDataPath = path.join(process.env.APPDATA || '', appName);
break;
case 'darwin': // macOS
appDataPath = path.join(os.homedir(), 'Library', 'Application Support', appName);
break;
case 'linux': // Linux
appDataPath = path.join(os.homedir(), '.config', appName);
break;
default: // Fallback for other platforms
appDataPath = path.join(os.homedir(), `.${appName}`);
}
return appDataPath;
}
// Function to get appropriate command based on OS
function getOpenCommand() {
const platform = os.platform();
switch (platform) {
case 'win32': // Windows
return 'start';
case 'darwin': // macOS
return 'open';
default: // Linux and others
return 'xdg-open';
}
}
// Example usage
const appName = 'myapp';
const appDataPath = getAppDataPath(appName);
const openCommand = getOpenCommand();
console.log(`OS Platform: ${os.platform()}`);
console.log(`OS Type: ${os.type()}`);
console.log(`Recommended App Data Path: ${appDataPath}`);
console.log(`Open Command: ${openCommand}`);
// Example of platform-specific behavior
console.log('\nPlatform-Specific Actions:');
if (os.platform() === 'win32') {
console.log('- Using Windows-specific registry functions');
console.log('- Setting up Windows service');
} else if (os.platform() === 'darwin') {
console.log('- Using macOS keychain for secure storage');
console.log('- Setting up launchd agent');
} else if (os.platform() === 'linux') {
console.log('- Using Linux systemd for service management');
console.log('- Setting up dbus integration');
}
// Example of checking for available memory and adjusting behavior
const availableMemGB = os.freemem() / (1024 * 1024 * 1024);
console.log(`\nAvailable Memory: ${availableMemGB.toFixed(2)} GB`);
if (availableMemGB < 0.5) {
console.log('Low memory mode activated: reducing cache size and disabling features');
} else if (availableMemGB > 4) {
console.log('High memory mode activated: increasing cache size and enabling all features');
} else {
console.log('Standard memory mode activated: using default settings');
}
// Example of CPU core detection for parallel processing
const cpuCount = os.cpus().length;
console.log(`\nCPU Cores: ${cpuCount}`);
const recommendedWorkers = Math.max(1, cpuCount - 1); // Leave one core for the system
console.log(`Recommended worker processes: ${recommendedWorkers}`);
Try it Yourself »
Summary
The Node.js OS module provides a powerful set of tools for interacting with the operating system.
With it, you can:
- Retrieve system information such as CPU architecture, platform, and release version
- Monitor memory usage and CPU performance
- Access user information like home directory and username
- Get network interface information
- Determine system uptime
- Use operating system-specific constants and end-of-line markers
These capabilities are particularly useful for:
- Building cross-platform applications that adapt to the host environment
- Monitoring system resources
- Creating diagnostic tools
- Making path and file-related operations that work correctly across different operating systems
- Optimizing application performance based on available system resources
By using the OS module, you can make your Node.js applications more robust, efficient, and adaptable to different operating environments.
Exercise?What is this?
Test your skills by answering a few questions about the topics of this page
Drag and drop the correct module that provides operating system-related utility methods and properties.
The module.
system
os
platform
sysinfo
