I love Ubuntu, and my wife says Mark Shuttleworth is "a nice young man,"
but when it comes to enterprise servers, Red Hat is the hands-down winner and still champion. Or, more accurately, a mix of Red Hat Enterprise Linux
(RHEL) and CentOS
is the choice of most high-end sysadmins I know.
There's a server cage in Chicago that runs several Web sites almost every FOSS user knows and uses regularly. The last time I checked, that cage held 44 identical rack-mounted Dell servers. 40 of them were running CentOS. Four of them were running Red Hat Enterprise Linux, complete with expensive Red Hat support contracts. The company's admins roll out all new software and all configuration changes on the RHEL servers first, so if any problems crop up that are beyond their own
(considerable) problem-solving abilities, they can call on Red Hat.
The company gets a lot of bang for their RHEL buck here. And Red Hat is aware that lots of companies, big and small, are doing the same thing.
Sure, it leads to a little teeth-grinding on the part of Red Hat executives, some of which I have witnessed first-hand, but the bright side of this RHEL/CentOS mixed deployment pattern is that Red Hat gets sales it wouldn't get if Ubuntu or another distro became dominant in the world's server rooms.
Developers, developers, developers
We all prefer software that's free both as in beer and as in freedom.
For example, I'm typing this article in Bluefish on an old laptop running Ubuntu GNU/Linux. That's about as free as you can get. But many enterprises end up running at least some non-free server-level software, even if their servers all run free operating systems. And if you look at what Linux distro commercial software companies universally supply binaries for, it's Red Hat.
The only exception to this is if you're mixing a lot of Microsoft software or old Novell NetWare with your Linux, in which case you may be better off with SUSE
Linux Enterprise Server as your supported Linux, and openSUSE as your free equivalent to CentOS.
Mind you, we're talking about servers here. Your server OS choice doesn't dictate your desktop choice, which can be any Linux distro you like, Mac OSX or even -- if absolutely necessary -- Windows.
Could someone else knock Red Hat off their throne?
Absolutely. Ubuntu's sponsoring corporation, Canonical, is working to do just that. So is Novell. And somewhere in a small town in Southern India, for all we know, two guys named Steve Rajiv and Steve Madurai might be working on an operating system they call Madras that will make all current OSes obsolete.
But right now, today, Red Hat Enterprise Linux, judiciously mixed with CentOS, is the default, "nobody ever got fired for choosing it," Linux choice for most server rooms.