How to fix Error: EMFILE: too many open files, open 'file.txt' in Node.js

# On Linux/macOS
ulimit -n

# Check both soft and hard limits
ulimit -Sn  # Soft limit
ulimit -Hn  # Hard limit

# Set limit to 4096
ulimit -n 4096

# Then run your Node.js application
node your-app.js

sudo nano /etc/security/limits.conf

* soft nofile 65536
* hard nofile 65536

[Service]
LimitNOFILE=65536

sudo systemctl daemon-reload
sudo systemctl restart your-service

npm install graceful-fs

// At the top of your entry file
const gracefulFs = require('graceful-fs');
gracefulFs.gracefulify(require('fs'));

// Or use it directly as a drop-in replacement
const fs = require('graceful-fs');

const fs = require('fs').promises;

async function readFile(path) {
  let fileHandle;
  try {
    fileHandle = await fs.open(path, 'r');
    const content = await fileHandle.readFile('utf8');
    return content;
  } finally {
    // Always close, even if reading fails
    await fileHandle?.close();
  }
}

// Or use streams which auto-close
const stream = fs.createReadStream('file.txt');
stream.on('close', () => console.log('Stream closed'));

npm install p-limit

const pLimit = require('p-limit');
const fs = require('fs').promises;

const limit = pLimit(10); // Process max 10 files concurrently

const files = ['file1.txt', 'file2.txt', /* ... */];

const promises = files.map(file => 
  limit(() => fs.readFile(file, 'utf8'))
);

const results = await Promise.all(promises);

const fs = require('fs');
const readline = require('readline');

const stream = fs.createReadStream('large-file.txt');
const rl = readline.createInterface({
  input: stream,
  crlfDelay: Infinity
});

for await (const line of rl) {
  // Process line by line without loading entire file
  console.log(line);
}