Unable to start new migration: failed to open stream: scandir(/opt/psa/var/modules/panel-migrator/sessions): failed to open dir

Symptoms

• Attempting to start a new migration going to Tools & Settings > Migration & Transfer Manager > Start a New Migration > Fill source server details > Click on Prepare migration, and migration fails to start with following error:

  PLESK_ERROR: Internal error ;-P
  ERROR: Zend_Config_Exception: file_get_contents(/opt/psa/var/modules/panel-migrator/sessions/20170603231643/config.ini): failed to open stream: No such file or directory (MigratorConfig.php:837)

  Or

  PLESK_ERROR: Internal error ;-P
  ERROR: Zend_Config_Exception: file_get_contents(/usr/local/psa/var/modules/panel-migrator/sessions/20180410114341/config.ini): failed to open stream: No such file or directory (Config.php:339)

• In Plesk log file /var/log/plesk/panel.log following error is shown:

  CONFIG_TEXT: PHP Warning: scandir(/opt/psa/var/modules/panel-migrator/sessions): failed to open dir: No such file or directory; File: /opt/psa/admin/plib/modules/panel-migrator/library/Backend/SessionManager.php, Line: 36

  Or

  CONFIG_TEXT: ERR [1] PHP Warning: scandir(/usr/local/psa/var/modules/panel-migrator/sessions): failed to open dir: No such file or directory; File: /usr/local/psa/admin/plib/modules/panel-migrator/library/Backend/SessionManager.php, Line: 40
  ERR [1] PHP Warning: file_put_contents(/usr/local/psa/var/modules/panel-migrator/sessions/20180411152303/config.ini): failed to open stream: No such file or directory; File: /usr/local/psa/admin/plib/modules/panel-migrator/vendor/plesk/migration-lib-code/src/Utils/FileUtils.php, Line: 31
  ERR [1] file_get_contents(/usr/local/psa/var/modules/panel-migrator/sessions/20180411152303/config.ini): failed to open stream: No such file or directory

Cause

$PLESK_ROOT_DIR/var/modules/panel-migrator/sessions directory doesn't exist.

Resolution

1. Connect via SSH
2. Create directory manually and set valid ownership and permissions:

   In Debian/Ubuntu:

   # mkdir /opt/psa/var/modules/panel-migrator/sessions
   # chown psaadm:root /opt/psa/var/modules/panel-migrator/sessions
   # chmod 0750 /opt/psa/var/modules/panel-migrator/sessions

   In CentOS/RedHat:

   # mkdir /usr/local/psa/var/modules/panel-migrator/sessions
   # chown psaadm:root /usr/local/psa/var/modules/panel-migrator/sessions
   # chmod 0750 /usr/local/psa/var/modules/panel-migrator/sessions