PHP warning: Failed to read session data: files session_start(): open(/var/) failed:

Symptoms

• Website hosted in Plesk displayed incorrectly or showing the PHP warning:PHP Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/sessions) in Unknown on line 0
• The following errors are found in Apache error_log for the website:

  # tail -f /var/www/vhost/system/example.com/logs/error_log
   ...
   mod_fcgid: stderr: PHP Warning: session_start(): open(/var/lib/php/sessions/sess_g0u8u3b1j8t98v0jpjmh0gmp84, O_RDWR) failed: No such file or directory (2) in /opt/www/vhost/example.com/httpdocs/wp-content/plugins/custom-sidebars/inc/external/wpmu-lib/inc/class-thelib.php on line 114, referer: http://example.com/
   ...
   mod_fcgid: stderr: PHP Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/sessions) in Unknown on line 0

  OR:

  # tail -f /var/www/vhost/system/example.com/logs/error_log
   AH01071: Got error 'PHP message: PHP Warning: session_start(): open(/var/lib/php/session/sess_d3deadbeef8i0455babecafeuo, O_RDWR) failed: Permission denied (13) in /home/www-data/example.com/httpdocs/index.php on line 2\nPHP message: PHP Warning: session_start(): Failed to read session data: files (path: /var/lib/php/session) in /home/www-data/example.com/httpdocs/index.php on line 2

Causa

The permissions for PHP session directory are incorrect or directory does not exist.

Solución

1. Log into Plesk and check the current session.save_path for domain in Domains > example.com > PHP Settings.

   Note: On Ubuntu or Debian, if session.save_path is not set, then session files are saved in /var/lib/php5, on RHEL and CentOS systems, if session.save_path is not set, session files will be saved in /var/lib/php/session.

2. Connect to the server via SSH and make sure the directory exists and have proper permissions (1733). If path is /var/lib/php/session:

   # stat /var/lib/php/session | grep Access
    Access: (1733/drwx-wx-wt) Uid: ( 0/ root) Gid: ( 0/ root)

   If directory does not exists create it and set valid permissions:

   # mkdir -p /var/lib/php/session && chmod 1733 /var/lib/php/session

   If directory exists but permissions are different, set the correct ones:

   # chmod 1733 /var/lib/php/session