PHP-FPM restart fails or website becomes unavailable after changing PHP handler for other domain: An another FPM instance seems to already listen on php-fpm.sock

Symptoms

• Unable to start or stop php-fpm or plesk-php**-fpm:

  # service php-fpm restart
  Stopping php-fpm: [FAILED]
  Starting php-fpm: ERROR: An another FPM instance seems to already listen on /var/www/vhosts/system/example.com/php-fpm.sock
  ERROR: FPM initialization failed
  [FAILED]

• There are several duplicates of the file .sock in different PHP handlers for the same domain:

  # ls -l /etc/php-fpm.d/example.com.conf && ls -l /opt/plesk/php/5.6/etc/php-fpm.d/example.com.conf
  -rw-r--r-- 1 root root 1342 Nov 19 04:13 /etc/php-fpm.d/example.com.conf
  -rw-r--r-- 1 root root 1308 Nov 19 13:57 /opt/plesk/php/5.6/etc/php-fpm.d/example.com.conf

• When changing PHP handler version in Domains > example.com > PHP Settings, some of the other domains using the target handler become unavailable with error 503

  AND

• The following entries are found in the affected domains' log files (/var/www/vhosts/system/example.com/logs/error_log):

  CONFIG_TEXT: (111)Connection refused: AH02454: FCGI: attempt to connect to Unix domain socket /var/www/vhosts/system/example.com/php-fpm.sock (*) failed

Cause

This is a Plesk bug with ID PPPM-6963, that has already been fixed in Plesk Onyx 17.8.

Both handlers, PHP-FPM by Plesk and PHP-FPM by OS vendor, use the same socket file. Such behavior occurs, when a domain was renamed or switched to a different PHP-FPM version. In case both handler processes are simultaneously stopped and then started one by one, the latter one fails.

Resolution

Upgrade Plesk to Onyx 17.8.

• How to upgrade Plesk to the next release?

As a temporary workaround, perform the following steps:

1. Connect to the Plesk servervia SSH.

2. Move configuration files of the domains mentioned in the error message from both locations:

   # mv /etc/php-fpm.d/example.com.conf{,.bak}
   # mv /opt/plesk/php/5.6/etc/php-fpm.d/example.com.conf{,.bak}

3. Restart PHP-FPM:

   # service php-fpm start