I was bummed out when the Gentoo maintainers removed osiris from portage due to inactivity. Because of this I had to 'unmask' this package to keep my system somewhat happy. I've been a big fan of osirisd/osirismd for a long long time. I think it's the best file integrity checker out there. I always hated systems that kept the database on the host. These should be stored on a remote host. Samhain does something similar, but osiris is just so simple and clean. It's absolutely perfect.
Today, I saw that osiris is back in portage and with the latest version of 4.2.3. I do have a lot of client hosts, so I figured I would spend most of the day upgrading to this version, but the upgrade went extremely smooth. Simply emerging osiris on all boxes and restarting osirisd on the clients and osirismd on the host and I was back up and running in no time.
Thanks Gentoo for bringing it back!
On that note, I came across this book at amazon (Host Integrity Monitoring Using Osiris and Samhain), and picked it up. I'll let you know what I think after it get's here.