Website is slow: open_basedir restriction in effect. File is not within the allowed path(s)

Symptoms

• Website or particular pages show one of the following errors:

  CONFIG_TEXT: 500 Internal Server Error

  OR

  CONFIG_TEXT: This page isn’t working
  HTTP ERROR 500

• Some website functionality is not working, e.g. the contact form.

• Website is slow.

• The following row appears in the /var/www/vhosts/system/example.com/logs/error_log or /var/log/plesk-phpXX-fpm/error.log file:

  Note: phpXX in the path above is the corresponding PHP version used on the website.

  CONFIG_TEXT: [fcgid:warn] [pid 100430] [client 203.0.113.2:35696] mod_fcgid: stderr: PHP Warning: is_file(): open_basedir restriction in effect. File(/usr/bin/test.php) is not within the allowed path(s): (/var/www/vhosts/example.com/:/tmp/) in /var/www/vhosts/example.com/httpdocs/index.php on line 564, referer: http://www.example.com

• The mentioned file paths do not exist on the system:

  # ls -al /usr/bin/test.php
  ls: cannot access '/usr/bin/test.php': No such file or directory

Cause

Website code issue: there are referrals to non-existent files.

Resolution

Contact the website developers to review the website code.

Additional information

The other causes of such error are addressed in the articles below:

A website hosted in Plesk is not accessible: open_basedir restriction in effect

WordPress shows 500 Internal Server Error on Windows: open_basedir restriction in effect