I just wanted to give everyone a heads up that in response to repeated bug reports about failure to reboot after a Virtualmin installation due to kernel bugs on CentOS, Fedora and RHEL, I have removed the update process that was previously being triggered at the end of a Virtualmin installation.
I strongly recommend you update your systems before putting them into service, but be aware that CentOS/Fedora/RHEL have recently been rolling out kernels that simply won't boot on some hardware (my laptop and qemu systems exhibit this problem with some of the recent kernels, while my desktop and virtualmin.com do not...so it's about 50% in my experience, but my data set is limited).
Anyway, it's not our fault! I thought I was picking the lesser of two evils by triggering a full system update at the end of the installation, but it's looking like customers aren't happy with that decision (it also makes it look like the install takes a really long time and requires gigabytes of downloads for folks who have an all-packages install and have never updated their system).
So, in short, if you've installed Virtualmin and couldn't boot afterward, it's a buggy kernel from your OS vendor. Reboot and select an older kernel, and all should be well. We have no control over it and can't fix it. But I promise not to make the problem exhibit in the future.
I can learn from my mistakes. If I have to. ;-)