Guides'Old' Linux Kernels Stay Fresh

‘Old’ Linux Kernels Stay Fresh

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For many in the world, it’s the time of year for wrapping up the old and moving ahead with the new. That’s not necessarily the case for Linux, though. For the Linux kernel, what’s old is new again with the new releases of the and 2.4.34 kernels.

Out with the old, in with the new isn’t the case in the Linux community, where the 2.4.x and 2.6.16.y kernels are in use and continue to be developed.

The current Linux kernel, version 2.6.19, was
released at the end of November and work is ongoing for an early 2007
release of the 2.6.20 kernel. But that’s not stopping developers from putting
out releases of older Linux kernels.

Currently, both the 2.4.x Linux kernel and the 2.6.16.y kernel are being
actively maintained, and both legacy kernels have recently released new

Adrian Bunk, the maintainer of the Linux 2.6.16.y kernel, officially released
the 2.6.37 release today. The first 2.6.16 kernel was originally
released in March and was soon replaced as the leading-edge kernel in June with the 2.6.17

In August, Linux kernel developer Greg Kroah-Hartman announced that Bunk would be taking over the maintenance of the 2.6.16-stable kernel branch. At the time Kroah-Hartman wished Bunk well but doubted the effort
could last very long. So far, Bunk is proving Kroah-Hartman wrong.

That said, Bunk admitted that the further away 2.6.16.x will become from
Linus Torvalds’ tree, the harder it will be to maintain.

“It’s therefore clear that the number of ‘nice to have’ things like
non-security bug fixes and the small amount of safe patches for additional
hardware support I’m currently adding to 2.6.16.x will greatly decrease as
time passes by,” Bunk told

“The must-have of adding security fixes will also become similarly harder,
but I’d expect that this will still be possible for a long time, especially
considering that such fixes will anyway be made from distributions
supporting 2.6.16 or nearby kernels for many years,” Bunk added.

Though it’s not at the head of Torvalds’ current Linux
development effort, there is still a demand and a need for a stable and
maintained 2.6.16.y kernel. Bunk explained the target audience for the
2.6.16.y kernel is users who are building their own kernels and who want
security updates but no regressions.

“These people did otherwise have the choice between following Linus’ tree
that unfortunately contains frequent regressions or staying with an old
kernel getting more and more known security vulnerabilities,” Bunk said.

It’s not known, however, exactly how many people need or want a
maintained 2.6.16.y kernel.

“I have some sporadic feedback from users and zero idea how many users
2.6.16.x has,” Bunk commented. “But that doesn’t matter, it’s simply an

Bunk is not alone in his efforts at trying to maintain an older Linux kernel.
Willy Tarreau currently maintains the even older 2.4.x Linux kernel, which
was supplanted by the 2.6.x kernel in December 2003.

Tarreau took over the maintenance of the 2.4.x kernel from Marcelo Tosatti in August of this year. Tarreau released version 2.4.34 of the Linux Kernel on Dec. 23.

The reason Tarreau is maintaining the 2.4.x kernel, even though it’s
three years past its prime, is quite simple. He needs it to do his job.

“I work at Exosec where we use Linux to provide managed services, and to
build appliances,” Tarreau told “Just like several
other true appliances makers, we still rely on 2.4 because its stability
allows our customers to focus on their job instead of firmware updates.”

“Part of my time at Exosec is spent working on the kernel, sometimes for our
own needs, sometimes to merge other people’s patches,” Tarreau continued.
“There are also a few distro vendors still supporting 2.4 who spontaneously
send me fixes from time to time.”

New bug fixes in the mainline 2.6.x branch of the kernel could be backported
to the 2.4.x kernel, though that’s not typically necessary according to

“Just a few of the 2.6 bugs affect 2.4,” Tarreau said.

It’s not all about fixes for 2.4.x, either. In fact there have even been some
small enhancements made, as well. In particular Tarreau noted support for GCC 4, which was contributed by Mikael Pettersson.

Tarreau currently doesn’t know how long he’ll be maintaining the 2.4.x
kernel for and it’s not clear when end of life for the old kernel will

“One year ago, some people told me they would switch to 2.6 within six months,
and their migration plans have not evolved yet, so it’s hard to tell when
this will end,” Tarreau said. ” When we won’t be using 2.4 anymore and there
will be no demand for it anymore, I may pass it to someone else or keep it
just because it won’t induce much work.

“Then, maybe I will switch over to a long-term 2.6 branch in the hope to
keep providing a high quality to our customers.”

This article was originally published on

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