Fedora 16, and they changed everything. Well, not everything, but a fair bit. I hate it when they do that, I have to learn a whole new set of stuff, and then it's relevant for some versions, and the old way is relevant for others.
For example, SELinux (Security Enhanced Linux). That's to stop users messing with each other's stuff. Like so many security systems, it brings with it many pains in the arse, and since I only have one user on each server (me) I don't need it, so I disable it when I install Linux. With versions 6 to 12, and probably others, you did that from the GUI, you just started the SELinux controller, clicked on Disable and that's done. With 16, you can't. You edit /etc/selinux/config and set it to disable. Maybe there's another way, but the point is, it's *different*.
Also. There used to be /etc/init.d/rc3.d and under that, there would be a bunch of services like S60nfs (which told the system to start up the NFS server on power-up). And there was a user interface that made it easy to disable some services that I didn't want, and enable others. So, they changed that. So, how did I know it was /etc/init.d/rc3.d? Well, I just did, from years of use. And now it's all different. Ugh. And how do you start up a service? It used to be "/etc/init.d/nfs start" and now it's "systemctl start nfs-server.service". I don't mind changes when it makes things better, but when something that used to work no longer works, for no good reason, that's annoying. I mean, they could have made "/etc/init.d/nfs start" translate to "systemctl start nfs-server.service" without me having to do anything, but they didn't.
Although /etc/init.d/httpd start still works. Logic? We've heard of it.
And I also found that although Fedora 16 would install nicely on my Foxcomm motherboards, it won't install on my Gygabyte motherboards (although Fedora 15 will). I try to boot from a CD, and it refuses to boot from the CD. I have no idea why. Computers are like that, and I wasted ages trying to fault-find before I worked that out.
One system I did today; when I powered it up, nothing happened. Not a surprise, it was like that when I took it down. I didn't know why it was dead, but now I do - the PSU is knackered. With a replacement PSU (and I also changed the memory sticks, the old ones were duff also) it started up fine. It turns out that PSU failure is the second commonest hardware problem I get (the commonest is hard drive failure, the third is memory stick failure).
And the power supply tester I just bought for a few pounds came in handy here, letting me verify that the old one is dead, and checking that the replacement is up to snuff.