phpMyAdmin is not working: session_start(): Failed to read session data: files (path: ./tmp/session)

Symptoms

• The following error message occurs on an attempt to open phpMyAdmin in Domains > example.com > Databases or in Tools & Settings > Database Servers > next to the MySQL server name:

  CONFIG_TEXT: Error during session start; please check your PHP and/or webserver log file and configure your PHP installation properly. Also ensure that cookies are enabled in your browser.
  
  session_start(): open(SESSION_FILE, O_RDWR) failed: No such file or directory (2)
  session_start(): Failed to read session data: files (path: ./tmp/session)

• The following entry is found in /var/log/syslog/:

  CONFIG_TEXT: GenerationTree mysql[1457]: ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

• SessionSavePath is set to ./tmp/session:

  Debian, Ubuntu:

  # grep -rin 'SessionSavePath' /opt/psa/admin/htdocs/domains/databases/phpMyAdmin/libraries/config.default.php
  716:$cfg['SessionSavePath'] = './tmp/session';

  CentOS:

  # grep -rin 'SessionSavePath' /usr/local/psa/admin/htdocs/domains/databases/phpMyAdmin/libraries/config.default.php
  716:$cfg['SessionSavePath'] = './tmp/session';

• phpMyAdmin package is not configured:

  # dpkg -l | grep -i phpmyadmin
  iU psa-phpmyadmin 4.8.3-ubuntu16.04.build1708180919.15 all MySQL web administration tool adapted for Plesk Onyx

Cause

The package psa-phpmyadmin is not configured.

The proper SessionSavePath should be /opt/psa/var/phpMyAdmin/session for Debian/Ubuntu or /usr/local/psa/var/phpMyAdmin/session for CentOS.

Resolution