Unable to start PHP-FPM if no domains are assigned to it: No pool defined. at least one pool section must be specified in config file

Symptoms

Unable to start PHP-FPM if no domains are using it:

Note: plesk-php56-fpm is used as an example.

• The command below reports that PHP-FPM is not in use by any domain:

  # plesk bin php_handler --get-usage -id plesk-php56-fpm
  The PHP handler with ID "plesk-php56-fpm" is not used.

• There are no (zero) configuration files inside a PHP-FPM pool directory:

  # ls /opt/plesk/php/5.6/etc/php-fpm.d/* | wc -l
  ls: cannot access /opt/plesk/php/5.6/etc/php-fpm.d/*: No such file or directory
  0

• The following error message appear in /var/log/plesk-php56-fpm/error.log:

  ERROR: No pool defined. at least one pool section must be specified in config file

• Going to Tools & Settings > Services Management > Plesk PHP-FPM 5.6 service cannot be started, its status is disabled as follows:

  

Cause

This is expected behavior: If a PHP-FPM handler is not in use by any of domains, it will not start.

When a domain will be switched to this PHP-FPM handler, its PHP-FPM service will start automatically.

Resolution

To start using a particular PHP-FPM version, just assign it to any domain at Domains > example.com > PHP Settings. The service will be started automatically.