Here I sit, watching a freshly installed FreeBSD box run through cvsup on all ports, to be closely followed by a new kernel compilation. As the output flies by in the xterm, I find myself wondering why I don't run into more FreeBSD in the world.
The truth is that I've been using some form of BSD since 1993 or so (the days of BSD/386). A foundational server that I've run since 1995 used BSDi initially, transitioning to FreeBSD back in the 3.0 release days. I can't contemplate using any other OS for this box and the myriad tasks it performs. We're not talking about a system that sits idle most of the time; this box generally deals with 250,000 to 300,000 emails a day (mostly spam, which produces a heavier load than actual mail delivery), and it serves up DNS, Web, and SMTP/POP/IMAP services for dozens of domains. It generally hovers at a load of 0.50 with the occasional spike.
Right up until last week, this FreeBSD box had an uptime of 1,057 days, or nearly three years. This streak was broken only due to a UPS failure during a brief power outage. It rebooted with nary a hitch. However, this event caused me some concern over the age of the hardware and the install itself, since it's still running a patched 6.1 release on a 10-year-old Compaq Evo W6000 workstation with a couple 1.7GHz Xeon CPUs and 2GB of RDRAM. (Yes, that's right -- Rambus.) And this box has been rock-solid stable the entire 10 years, with only a disk failure or two in the middle.
I attribute most of that longevity and stability to the OS. Sure the hardware plays a part, but make no mistake: FreeBSD is a fantastically stable and reliable operating system. In fact, all the *BSDs are: NetBSD, OpenBSD, TrustedBSD, and the like. As we know, BSD forms the foundation of OS X, albeit with the Mach kernel. There's a reason for that -- stability, reliability, and the forgiving licensing.
Beyond the stability, FreeBSD was way ahead of Linux with significant features like DTrace and ZFS. In fact, Linux still doesn't officially have native ZFS support, though Lawrence Livermore National Laboratory is working on exactly that through a contract with the DOE. Then there's the matter of FreeBSD's pf firewall that is much simpler and more powerful than Linux's iptables, and the BSD TCP stack is generally known as the reference implementation, and it's used in many internetnetworking speed tests for this reason.