https://fedorahosted.org/spacewalk/wiki/HowToInstall
with sizing options and pre-reqs that need to be met. One major note is that the installation will not proceed smoothly if you're using the postgresql install, you need to have a fairly big mount point at /var/lib/pgsql or the installation of spacewalk will stall. I sized mine to be 20GB, but that may be overkill.
After basic server setup, to install spacewalk with postgre sql, the general steps are below
1. Install the spacewalk repository on your centos/rhel6 system
rpm -Uvh http://yum.spacewalkproject.org/2.3/RHEL/6/x86_64/spacewalk-repo-2.3-4.el6.noarch.rpm
2. ensure you have the jpackage repo installed as well
cat > /etc/yum.repos.d/jpackage-generic.repo << EOF [jpackage-generic] name=JPackage generic #baseurl=http://mirrors.dotsrc.org/pub/jpackage/5.0/generic/free/ mirrorlist=http://www.jpackage.org/mirrorlist.php?dist=generic&type=free&release=5.0 enabled=1 gpgcheck=1 gpgkey=http://www.jpackage.org/jpackage.asc EOF
3. Run the command yum install spacewalk-setup-postgresql to obtain the spacewalk database setup program
4. Install the spacewalk application using yum install spacewalk-postgresql
5. Run spacewalk-setup --disconnected to complete the spacewalk setup.
