Website on Plesk error: 503 Service Temporarily Unavailable: failed to make connection to backend: httpd-UDS

Symptoms

• Websites are unavailable:

  503 Service Temporarily Unavailable

• The following is shown in the log file /var/www/vhosts/system/example.comlogs/error_log

[Thu Dec 03 16:27:53.524474 2020] [proxy_fcgi:error] [pid 720157:tid 140230787532544] [client 127.0.0.1:54106] AH01079: failed to make connection to backend: httpd-UDS
[Thu Dec 03 16:27:55.900259 2020] [proxy:error] [pid 719987:tid 140230670034688] (13)Permission denied: AH02454: FCGI: attempt to connect to Unix domain socket /var/www/vhosts/system/example.com/php-fpm.sock (*) failed

• The next error is shown when trying to obtain information about PHP from Domains > Example.com > PHP Settings > View the phpinfo() page

• Error: Unable to retrieve information about the PHP configuration.

  File ownership on /var/www/vhosts/system/example.com is not root:psaserv and/or permissions are not 711, for example:

  # ls -lsd /var/www/vhosts/system/example.com

  0 drwxr-x--- 7 root root 89 3. Dez 15:13 /var/www/vhosts/system/example.com

Cause

File permissions and/or ownership are incorrect.

Resolution

1. Log in to Plesk server via SSH
2. Fix ownership and permissions:

   # chown -R root:psaserv /var/www/vhosts/system/example.com
   # chmod -R 711 /var/www/vhosts/system/example.com

3. Go to Domains > example.com > PHP Settings and change the PHP version to a different one and then back to the one that needed in order to re-generate and re-validate the configuration files.