Noticed a lot of questions about this, couldn't easily find a simple answer ( a lot of them were far too involved)
So I am posting this in the hope that it will help.
Install zoneminder from the repositories.
Apache and MySQL will also be installed, if they are not already.
It will ask you for a MySQL root username and password DO NOT FORGET THIS.
Add a link in the apache (webserver) config directory
$ sudo ln -s /etc/zm/apache.conf /etc/apache2/conf.d/zoneminder.conf
If apache is not running, start it
$ sudo /etc/init.d/apache2 start
If apache is already running, restart it
$ sudo /etc/init.d/apache2 force-reload
$ sudo chmod 4755 /usr/bin/zmfix
$ zmfix -a
$ sudo adduser www-data video
Shared memory settings need to be chnaged for ZoneMinder
$ sudo nano /etc/sysctl.conf
add this at bottom (128 MB)
kernel.shmall = 134217728 kernel.shmmax = 134217728
save and exit.
TEST http://localhost/zm should open Zoneminder screen.
Default user=admin password=admin
(Thanks to the various posts that I garnered this from)
I am running this on my Mythbuntu install, but it should work for Standard Ubuntu too.