Debugging session_start() Errors in PHP Using Error Logs

Enable Error Logging in PHP

To get detailed error messages, enable error reporting in php.ini.

For related session and PHP-debug topics, see Fixing session_start() failed: Permission denied (13), Fixing "No Space Left on Device (28)" & Session Write Errors, and Enable PHP Error Reporting for mysql.php Troubleshooting.

Locate php.ini

Find the active PHP configuration:

php --ini | grep "Loaded Configuration File"

Edit php.ini:

sudo nano /etc/php/8.0/apache2/php.ini

or (for PHP-FPM)

sudo nano /etc/php/8.0/fpm/php.ini

Enable Error Display and Logging

Find and modify:

log_errors = On
error_log = /var/log/php_errors.log
display_errors = On
display_startup_errors = On

Restart PHP & Web Server

sudo systemctl restart apache2

or

sudo systemctl restart nginx php8.0-fpm

Now, PHP will log all errors to /var/log/php_errors.log.

Check Web Server Logs

Check Apache Logs

sudo tail -f /var/log/apache2/error.log

or (for CentOS/RHEL):

sudo tail -f /var/log/httpd/error_log

Check Nginx Logs

sudo tail -f /var/log/nginx/error.log

Check PHP Logs

If PHP is running as FPM (FastCGI Process Manager):

sudo tail -f /var/log/php8.0-fpm.log

Check System Logs for Security Restrictions

If the logs show "Permission denied (13)", SELinux or AppArmor may be blocking PHP.

Check SELinux Logs

sudo journalctl -xe | grep AVC

or

sudo grep "denied" /var/log/audit/audit.log

If SELinux is blocking PHP sessions:

sudo chcon -R -t httpd_sys_rw_content_t /var/lib/php/session

Check AppArmor Logs (Ubuntu/Debian)

sudo aa-status
sudo dmesg | grep php

If AppArmor is blocking PHP sessions:

sudo aa-complain /usr/sbin/php-fpm

Debug with a Test Script

If no useful logs appear, create a PHP debug script.

Create a File (debug.php)

sudo nano /var/www/html/debug.php

Paste this:

<?php
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);

session_start();

if (!session_id()) {
    echo "Session failed to start! Check logs.";
} else {
    echo "Session started successfully!";
}
?>

Run the Script in Browser

Go to:

http://yourserver.com/debug.php

or run from CLI:

php /var/www/html/debug.php

If an error appears, check logs and apply fixes accordingly.

Summary of Debugging Steps

By following these debugging steps, you can identify and fix session errors in PHP quickly.