RHEL6

Actually Red Hat currently supports a 2.4 series kernel in RHEL 3, and will do so into the middle of next year.

It is possible that Red Hat thinks supporting four releases at once was too much, and has decided, but not yet announced, that it will release RHEL less frequently, but with long phase 1 (new hardware and features) support. This might be a good choice because as the product matures, Microsoft have seen that customers become more and more resistant to upgrading. Rightly or wrongly they think it's an added cost (not a software cost, both Red Hat and Microsoft offer products where you don't pay for the specific version you use - but a training and testing cost) for no value.

So whereas you might have found customers would start using RHEL 4 on some production systems six months after it came out, and were using RHEL 5 within a year, Red Hat may have data that suggests if RHEL 6 was available today, it wouldn't drive any sales until 2011 anyway. So why spend the extra money on engineering? Wait until customers are begging for the new features, right?

Fedora offers them an advantage here. If Microsoft has some trouble that leaves them without even a beta of the new Windows Server for an extra year, they've got no way to put (server) features out there for customers to see. With Fedora, Red Hat gets an opportunity to show the way every six months, which must be good for customer confidence, while at the same time the rapid turnover of Fedora releases minimises ongoing engineering support overhead & makes it worthless for the roles where you might plausibly sell an RHEL license.

Ever bothered to look at RHEL 5 (5.4) kernel? You'll get an impression, it's not quite 2.6.18 anymore.

> And while we're at it ... whatever happened to the Red Hat desktop?

While I cannot comment on other ones, I am not sure what you mean here ... there is a commercially available desktop product http://www.redhat.com/rhel/desktop/ and of course Fedora servers pretty well as a desktop OS. I would be very sorry if it doesn't, because that's what I am employed to develop ;).

LWN has run a few articles regarding "Enterprise" kernels that address your questions. You seem to be overlooking the fact that Red Hat releases an updated RHEL-5 version about ever 6 months with a new 2.6.18 branch... and in doing so they always back-port drivers, some features, and security fixes. In the last few updates they have also seen fit to re-base some desktop apps on newer versions... or upgrade an app if the upstream has discontinued the base they were using (take Firefox for example in RHEL4).

RHEL's 2.6.18 is really 2.6.18 but with a significant amount of code from newer releases mixed in.

So to answer your question... how long can they continue to use it? That is like asking how long people can live in a house? As long as that house is continuously remodelled to meet the needs of the residents, it can go on until the planet gets destroyed.

Keeping kernel 2.6.18 as a base (read the same API) does have its advantages in the some commercial places. One of the suckiest thing about Fedora for me personally is running binary nvidia drivers which break often when new kernels come out.

By contrast, we maintain a commercial telephony IVR based on RHEL3. Its still in production, still works, and the company that owns it has no interest to update, with the exception of security updates. Due to redhat maintaining the same kernel release I was able to install yum on this machine, "yum update" over 600 packages (including the kernel), reboot and have the machine come straight back up, and start taking phone calls even without rebuilding the proprietry drivers for the IVR hardware.

A lot of purists will hate that, but in an unbiased world where you just want it to work (enterprise), it can be a major plus.

Even so we are running RHEL 3, 4 and 5 systems now and Im looking forward to RHEL6 for new installs. The old ones wont be updated so long as they still serve their purpose.