CentOS 7, openssh/openssl

Yesterday I finally gave CentOS 7 a try as a Virtualbox VM. (In the following, when I talk about a guest or a host, it's in the virtualization vernacular.)

I did what I usually do with VB guests: I gave it two network interfaces. The first is configured as NAT, so that the guest can reach the internet without the host needing a second IP for a bridged interface (bridging would be fine at home, but might cause me some trouble at work). The second is configured as host-only with a static IP, so that the host (and other guests) can initiate to the guest. (There’s probably a much easier way of doing this, but it’s worked so far.)

My CentOS experience is primarily with CentOS 5, and several things were really different in C7. (CentOS and Red Hat documentation is typically pretty good and will no doubt help me through some of the following. These are just some of the things I’m stumbling on at the moment.)

There’s no /etc/cron.daily/rpm, which creates a list of packages in /var/log/rpmpkgs. I use that a lot, so I copied that over from a C5 box.

I had a pretty hard time with networking. Neither interface seemed to come up on its own at first. I had to set ONBOOT=yes in the corresponding /etc/sysconfig/network-scripts files, and then the second interface mangled the first interface’s NAT connection. I ended up setting ONBOOT to yes for the first interface (the NAT connection) and to no for the second (host-only) interface. I put an ifconfig statement in rc.local to bring up the second interface, and that (eventually) worked.

ifconfig, netstat, and probably a bunch of other useful stuff is in the net-tools package, which isn’t included in a minimal install. And although there’s an rc.local, it’s not executable, and won’t run at boot until you “chmod +x” the thing.

And the interface names are now really weird. Instead of something memorable, traditional, predictable, and sensible like eth0 and eth1, now they are called enp0s3 and enp0s8. (I just had to look those up, because I couldn’t remember them.)

The new C7 guest has a very long list of iptables rules, but /etc/sysconfig/iptables doesn’t exist, so I don’t know where those rules are coming from. Thankfully port 22 is open by default, but I don’t like to run openssh on the default port, so at some point I’ll need to figure out how to fiddle with iptables rules.

I use GNU screen all the time. (I know the cool kids like tmux, but, frankly, screw them.) I typically have a screen session in which I’m logged in to several different hosts, and each window is named for the remote host. C7 rewrites the window name in screen, so “Ctrl-A ‘, hostname” no longer works. I don’t know if I need to (somehow) tell screen (on my Ubuntu host) not to allow the window process to rewrite the window title, or if I need to (somehow) tell bash in the C7 guest to be less assertive.

I’m also having some trouble building openssh from source in C7. The version of openssh that comes with C5 lacks some desirable features in the newer versions, so we tend to build it from source. In just the last version or two of openssh, something has changed such that it won’t build against the version of openssl that comes with C5. So the other day (before messing with C7) I built the newest version of openssl on a C5 box and built openssh against that. That worked, but I see now that by default openssl doesn’t create shared libraries, so the openssh I built linked to openssl statically (which made sshd nearly three times bigger than a dynamically-linked sshd).

So far I’ve been unable to build openssh against a source-built openssl on C7. I get one error if I try to link statically, and another error if I try to link dynamically. The version of openssl that comes with C7 is pretty current, so I could just build against that and probably have no problem. Likewise I could just use C7’s version of openssh. But although I’ve enjoyed the stability of C5, everything about it is pretty old at this point. I think that in the future I’d like to build many or all network services from source. Since openssh, apache, stunnel, and several others need openssl, I’d like to keep that current, too.

So I have some work ahead of me. I think C5 hits end-of-life some time in 2017, so I’ve got some time, but the C5 EOL will probably sneak up on me if I let it.