Long-time OpenBSD user here. OpenBSD has sane, secure defaults with nothing enabled in a fresh install. This is a desired default, as everyone uses OSes for different reasons. OpenBSD makes a phenomenal firewall, a pretty good Web server, and a super nice, secure file server.

OpenBSD shines because of the ongoing code audit, the minimalism, and the ability to easily make it into whatever you want. I don't care for any other OS for serious business. I will almost always use OpenBSD for servers, with RedHat or CentOS being the only other choice because of SELinux.

I would also venture to say that OpenBSD has the absolute best documentation of any OS out there, even better than FreeBSD.

Can you elaborate more on the CentOS/RedHat choice? I'm curious about how other Linux distros are handling in this space.

Sure. Some clients prefer us to use Linux, since their teams large or small are comfortable with it. OpenBSD is still a rather esoteric OS for most. I've been using both since 1998, so I can go either way. RedHat/CentOS offer support for 10 years is high up on the totem pole for me and plenty of others. OpenBSD releases every 6 months like most Linux distros, so some mission-critical users are uncomfortable with this pace, and I cannot say I blame them.

SELinux is great for areas that are into DAC/MAC/RBAC, plus the aforementioned lengthy support. I see more and more customers wanting Red Hat/CentOS than any other Linux distro and for good reason. It just works. Things like CPanel only run on these distros. Red Hat/CentOS are also very predictable and they offer superb documentation. More and more people are uncomfortable with things like Debian because there is no throat to choke if they need support or if something goes pear shaped.

I have worked on Linux for 20 years now and I have never, ever seen Debian or Slackware or even Ubuntu in a TRULY mission-critical role. People may disagree, but there are reasons why Red Hat/CentOS are chosen. They are typically very stable, use tested software, and are well documented for the use cases they excel in. Red Hat runs some truly mission critical stuff like power grids, and more and more SCADA systems, now that they are being upgraded due to threats.

>OpenBSD makes a phenomenal firewall

How about a router? I've been considering getting some single-board computer (probably an APU2[1]) and turning it into a router, possibly using OpenBSD + pf. Or maybe just install Pfsense. Or maybe use Linux and...iptables? (Not sure how that stack would look exactly)

1. https://www.pcengines.ch/apu2.htm

HardenedBSD (https://hardenedbsd.org) also. Which is a recent fork of FreeBSD that has a focus on security.

Unfortunately, HardenedBSD is nothing more but a PR campaign from a one person who feels rejected due to poor code quality and bad reviews from FreeBSD developers who expect a bit more than just throwing random patches around and saying 'here, I fixed all these security problems with three lines of code'. I would recommend taking HardenedBSD and its announcements with a huge portion of salt.

The funny part is that FreeBSD has had years to even implement anything as simple as ASLR but it didn't and instead starting to reject other peoples code. What HardenedBSD did is basically following the PaX model which has been documented for a long time[1]. It seems like FreeBSD is just lacking any developers willing to deal with these security features or let alone upstream it because its usually a pain in the ass to upstream stuff like this just look how Linux is having a hard time implementing even basic stuff from grsecurity. Exploit mitigations are not for fixing those security problems it is to make it harder to exploit certain vulnerabilities.

1: https://pax.grsecurity.net/docs/index.html

The funny part is that even amongst top security researchers there doesn't seem to be an agreement over the fact if ASLR is worth anything, as it was proved to be breakable in no time. And it seems like grsecurity code suffers the same problems as the code from HardenedBSD, that is the quality matching the respective project's standards.

Who are these top security researchers? ASLR on its own is useless but security is about layers there isn't one mitigation to rule em all. But ASLR combined with other features work very well, the funny part about FreeBSD that you can just apply 90s blog post about smashing the stack and you can exploit with it.

grsecurity code is clean and uses some neat tricks with the C language, most features have been there for at least a decade and recently things like RAP have come along but its all pretty clean. The problem with upstreaming is that you will have people that think the code is shit or doesn't work properly or all kinds of other stuff and that takes a lot of time that could be spent somewhere else. About the quality matching the respective project's standards is bullshit because many developers aren't security engineers or have never dealt with exploit mitigation's and instantly think/say the code is shit, biggest reason why Linux will never get actual important features from grsecurity because it takes lots of time and developers that actually understand what they are doing. FreeBSD just doesn't have those developers and neither has Linux, now you know why out of tree patches just work for this kind of stuff. Microsoft seems to take the upper hand in exploit mitigation's at the moment.