So we have a legacy server with Debian 6.0 !, the solution is to add LTS repository for Debian. I follow these instructions on turnkeylinux website.
First enable LTS updates on your Debian 6.0:
~# apt-get install -y debian-keyring debian-archive-keyring ~# cat>>/etc/apt/sources.list.d/security.sources.list<<'EOF' deb http://http.debian.net/debian/ squeeze-lts main contrib non-free deb-src http://http.debian.net/debian/ squeeze-lts main contrib non-free EOF
Update repositories and upgrade packages:
~# apt-get update ~# apt-get upgrade
Find which packages are not supported:
~# apt-get install -y debian-security-support ~# check-support-status
Now setup the unattended-upgrades like i described in [my blog], for more info go to debian wiki.