Plesk shows 500 Internal Server Error on Linux: [ERROR]: spawning fcgi failed

Symptoms

• Plesk login page is not available:

  CONFIG_TEXT: 500 Internal Server Error

• The following errors can be found in /var/log/sw-cp-server/error.log :

  CONFIG_TEXT: (mod_fastcgi.c.1068) the fastcgi-backend /usr/bin/sw-engine-cgi -c /usr/local/psa/admin/conf/php.ini -d auto_prepend_file=auth.php3 -u psaadm failed to start:
  (mod_fastcgi.c.1072) child exited with status 1 /usr/bin/sw-engine-cgi -c /usr/local/psa/admin/conf/php.ini -d auto_prepend_file=auth.php3 -u psaadm
  (mod_fastcgi.c.1075) If you're trying to run your app as a FastCGI backend, make sure you're using the FastCGI-enabled version.
  If this is PHP on Gentoo, add 'fastcgi' to the USE flags.
  (mod_fastcgi.c.1171) [ERROR]: spawning fcgi failed.
  (mod_fastcgi.c.3644) all handlers for /index.php? on .php are down.

Cause

The wrong permissions and owner were set for the /tmp directory and suexec binaries.

Resolution

1. Connect to the server via SSH

2. Set valid permissions for system directories:

   # chown root:root /tmp
   # chmod 1777 /tmp

   # chown root:apache /usr/sbin/suexec
   # chmod 4510 /usr/sbin/suexec

   # chown root:sw-cp-server /usr/lib64/sw-cp-server/sw-suexec
   # chmod 4710 /usr/lib64/sw-cp-server/sw-suexec

3. Restart sw-cp-server:

   # service sw-cp-server restart