Meet The Man Who Minds The Linux Kernel

Sean Michael Kerner

Linus Torvalds creates the Linux kernel, but Greg Kroah-Hartman maintains it. He speaks to Sean Michael Kerner

Linus Torvalds, the founder and creator of the open-source Linux operating system, releases a new Linux kernel every 10 to 12 weeks, but not all Linux kernels have a long life and not all kernels are stable enough for enterprise or consumer electronics usage. The kernel is the heart of a Linux operating system, and updates provide new capabilities, including system architecture, filesystem, networking and driver support.

Earlier this month, Greg Kroah-Hartman, a Fellow at the Linux Foundation, declared that the recent Linux 3.10 kernel release that first debuted at the end of June will be a long-term kernel release. A long-term Linux kernel release is maintained by Kroah-Hartman for up to two years. In contrast, a non-long-term kernel release is no longer maintained after a new kernel is released. For example, the Linux 3.9 kernel that first debuted in April of this year hit its end of life at the end of July, shortly after Linux 3.10 debuted.

greg-kroah-hartman linux kernelWhy is Linux 3.10 so good?

As to why and how the Linux 3.10 kernel was chosen as the next long-term release, Kroah-Hartman explained to eWEEK that he spent a lot of time talking with many companies about their product plans for the year. Linux is pervasive in consumer electronics as well as in server and mobile operating system infrastructures. Kroah-Hartman said he talked to companies about what kernels they wanted to use based on what features they contained, and their development cycles.

“The 3.10 kernel ended up being the best fit for the largest number of different companies that I could find,” Kroah-Hartman said.

In the Linux development world, there is not just one long-term kernel. In fact, currently there are no less than five, including the,, 3.0.89, 3.2.50 and 3.4.56 kernels that are all being maintained for longer than a release cycle.

Kroah-Hartman currently maintains three of those long-term kernels, each of which has a different end-of-life date. The Linux 3.0 kernel first became generally available in July 2011 and will be maintained until October 2013. The Linux 3.4 kernel first shipped in May 2012 and will be maintained by Kroah-Hartman until 2014. The new 3.10 long-term kernel first debuted in June of this year and will be maintained until September 2015.

Who uses the kernel?

There are a number of different use cases and vendors that use the long-term Linux kernel. One is Linux distribution vendor SUSE, which uses the 3.0 long-term kernel for its enterprise release.

“There are also lots and lots of Android devices based on 3.0 and 3.4 still being created,” Kroah-Hartman said. “There are also lots of companies that just base their product on the long-term kernel, or the LTSI (Long Term Support Initiative) kernel, which is based on the long-term kernel, and ship it and don’t say anything back to me, as it just works for them and they can rely on the constant stream of security and general bug fixes to update their product with.”

The LTSI is a multivendor consumer electronics effort led by the Linux Foundation and supported by Hitachi, LG Electronics, NEC, Panasonic, Qualcomm Atheros, Renesas Electronics, Samsung Electronics, Sony and Toshiba. The goal of LTSI is to have a stable, common Linux base that is suitable for use in consumer electronics devices.

The long-term Linux kernel effort itself is just two years old, having initially been proposed by Kroah-Hartman only in 2011. Overall he said that he thinks the effort has been working well, though there are some challenges.

“My biggest challenge is handling so many kernels at once,” Kroah-Hartman said. “I can do three pretty easily, but for some reason, adding a fourth one seems to cause me problems, which is one primary reason I don’t want to maintain any of these for longer than two years.”

After two years, he said, the amount of patches that end up being relevant to an older kernel drops way down, so it is easier to move on to a newer one at that point in time.

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Originally published on eWeek.