How to fix Error: EAGAIN: resource temporarily unavailable in Node.js

# Check maximum open file descriptors
ulimit -n

# Check maximum user processes
ulimit -u

# View all limits
ulimit -a

# Count open file descriptors for current process
ls /proc/$$/fd | wc -l

# For a specific Node.js process
ls /proc/<PID>/fd | wc -l

const fs = require('fs');

function readWithRetry(fd, buffer, offset, length, position, maxRetries = 3) {
  let retries = 0;

  while (retries < maxRetries) {
    try {
      return fs.readSync(fd, buffer, offset, length, position);
    } catch (error) {
      if (error.code === 'EAGAIN' && retries < maxRetries - 1) {
        retries++;
        // Brief delay before retry
        const start = Date.now();
        while (Date.now() - start < 10) {} // 10ms blocking wait
        continue;
      }
      throw error;
    }
  }
}

async function readWithRetryAsync(fd, buffer, offset, length, position, maxRetries = 3) {
  for (let i = 0; i < maxRetries; i++) {
    try {
      return await fs.promises.read(fd, buffer, offset, length, position);
    } catch (error) {
      if (error.code === 'EAGAIN' && i < maxRetries - 1) {
        await new Promise(resolve => setTimeout(resolve, 10));
        continue;
      }
      throw error;
    }
  }
}

# Increase file descriptor limit
ulimit -n 4096

# Increase process limit
ulimit -u 2048

* soft nofile 4096
* hard nofile 8192
* soft nproc 2048
* hard nproc 4096

[Service]
LimitNOFILE=4096
LimitNPROC=2048

const fs = require('fs');
const { spawn } = require('child_process');

// Always close file descriptors
const fd = fs.openSync('file.txt', 'r');
try {
  // perform operations
} finally {
  fs.closeSync(fd);
}

// Use graceful-fs for automatic retry handling
const gracefulFs = require('graceful-fs');
gracefulFs.readFile('file.txt', 'utf8', (err, data) => {
  // graceful-fs automatically retries on EAGAIN
});

// Properly manage child processes
const child = spawn('command', ['arg1', 'arg2']);

child.on('exit', (code) => {
  console.log(`Process exited with code ${code}`);
});

child.on('error', (error) => {
  if (error.code === 'EAGAIN') {
    console.error('Resource temporarily unavailable, retry later');
  }
});

// Limit concurrent child processes
const MAX_CONCURRENT = 10;
let activeProcesses = 0;
const queue = [];

function spawnWithLimit(command, args) {
  if (activeProcesses < MAX_CONCURRENT) {
    activeProcesses++;
    const child = spawn(command, args);
    child.on('exit', () => {
      activeProcesses--;
      if (queue.length > 0) {
        const next = queue.shift();
        spawnWithLimit(next.command, next.args);
      }
    });
    return child;
  } else {
    queue.push({ command, args });
  }
}

npm install graceful-fs

// Instead of:
// const fs = require('fs');

// Use:
const fs = require('graceful-fs');

// All fs operations now automatically retry on EAGAIN
fs.readFile('file.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error after retries:', err);
    return;
  }
  console.log(data);
});

const gracefulFs = require('graceful-fs');
gracefulFs.gracefulify(require('fs'));