Fix: Session_start(): Cannot start session error

The ‘Session_start(): Cannot start session’ error occurs when PHP cannot initialize a session due to headers already sent, permission issues, or misconfigured session settings.

How the Error Happens

❌ Error Scenario:

// ❌ This causes the error
echo "Some output"; // ❌ Headers sent before session_start()
session_start(); // Fatal error: session_start(): Cannot start session

✅ Quick Fix - Proper Session Configuration

Solution 1: Check for Output Before Session Start

<?php
// ✅ No output before session_start()
session_start();

// ✅ Now you can use session variables
$_SESSION['user_id'] = 123;
?>

Solution 2: Configure Session Settings

<?php
// ✅ Set session configuration before starting
ini_set('session.save_path', '/tmp');
ini_set('session.cookie_httponly', 1);
ini_set('session.use_strict_mode', 1);

// ✅ Start session after configuration
session_start();
?>

Solution 3: Check Session Directory Permissions

<?php
// ✅ Verify session directory is writable
$sessionPath = ini_get('session.save_path') ?: '/tmp';
if (!is_writable($sessionPath)) {
    // ✅ Set alternative session path
    session_save_path('/tmp');
}

session_start();
?>

Solution 4: Use Output Buffering

<?php
// ✅ Start output buffering to prevent premature output
ob_start();

// ✅ Any output happens here but is buffered
echo "Some content";

// ✅ Start session after ensuring no headers sent
session_start();

// ✅ Send output after session starts
ob_end_flush();
?>