I have a minimal Debian 7 box and install Horde from this instructions: https://wiki.debian.org/Horde.
Request on http://localhost/horde
gives
A fatal error has occurred
This system is currently deactivated.
Details have been logged for the administrator.
When going to http://localhost/horde/test.php
the page complains for
Required Configuration Files
config/conf.php: No
You need to login to Horde as an administrator and create the configuration file.
In /srv/www/horde/horde/config I have:
$ cp conf.php.dist conf.php
$ ll conf.php
-rw-r--r-- 1 www-data www-data 3457 Jan 9 11:12 conf.php
Apache2 runs with default site with sym link in /var/www/horde -> /srv/www/horde
.