When listing host on Foreman
Operating system field Is empty for wheezy (debian testing)
Maybe also empty for Unstable

On lenny:
Operating System -> Debian 5.0
On squeeze:
Operating System -> Debian 6.0

1. On squeeze

facter |grep "lsb\|operating"

lsbdistcodename => squeeze
lsbdistdescription => Debian GNU/Linux 6.0.5 (squeeze)
lsbdistid => Debian
lsbdistrelease => 6.0.5
lsbmajdistrelease => 6
operatingsystem => Debian
operatingsystemrelease => 6.0.5

1. On wheezy

cat /etc/debian_version

wheezy/sid

dpkg -l |grep lsb

ii lsb-base
ii lsb-release

facter |grep "lsb\|operating"

lsbdistcodename => wheezy
lsbdistdescription => Debian GNU/Linux testing (wheezy)
lsbdistid => Debian
lsbdistrelease => testing
lsbmajdistrelease => testing
operatingsystem => Debian
operatingsystemrelease => wheezy/sid