Site opening 500 error or blank page: Operation not permitted in Unknown on line 0

Symptoms

• After the migration, WordPress domain is not available with 500 error or a white page;

• The same behaviour may appear if a main domain of a subscription was renamed;

• Wordfence plugin is installed for the domain;

• The following errors may be found in /var/www/vhosts/example.com/logs/error.log or /var/www/vhosts/main.domain/example.com/logs/error.log:

  CONFIG_TEXT: [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: open_basedir restriction in effect. File(/var/www/vhosts/example.com/httpdocs/kc080517/wordfence-waf.php) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in Unknown on line 0
  [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: failed to open stream: Operation not permitted in Unknown on line 0
  [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: open_basedir restriction in effect. File(/var/www/vhosts/example.com/httpdocs/kc080517/wordfence-waf.php) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in Unknown on line 0
  [warn] [client 203.0.113.2] mod_fcgid: stderr: PHP Warning: Unknown: failed to open stream: Operation not permitted in Unknown on line 0

Cause

Wordfence plugin configuration was not migrated properly.

Resolution

Check Wordfence configuration files and correct them accordingly,  delete the plugin if required.