Horde shows Service Temporarily Unavailable: Connection reset by peer: mod_fcgid: error reading data from FastCGI server

Symptoms

Unable to access Horde webmail:

Service Temporarily Unavailable  The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later.

The following message appears in /var/log/httpd/suexec_log:

[2016-12-23 14:43:08]: uid: (16/horde_sysuser) gid: (10285/10285) cmd: cgi_wrapper
[2016-12-23 14:43:08]: crit: cannot run as forbidden uid (16/cgi_wrapper)

Cause

Incorrect UID set for horde_sysuser .

Resolution

1. Create a backup of /etc/passwd file.
2. Select any UID more than 100 and make sure it is not assigned to any user.
3. Change UID for horde_sysuser in /etc/passwd file:
   

   # grep horde /etc/passwd
   horde_sysuser:x:494:507:horde webmail user:/usr/share/psa-horde:/sbin/nologin

4. Re-create web server configuration files:
   

   # plesk repair web -server