LTSI Development Guide

1. LTSI Concept.

 LTSI kernel is based on upstream LTS kernel maintained by Greg Kroah-Hartman. LTSI sync with every LTS migration to reflect all bug/security fixes applied to LTS kernel[1].

 A new LTSI Kernel release should come out once a year, and the release will be maintained for 2 years from its original kernel release date. Be noted that it is not from the LTSI kernel release date. During these 2 years, there will be minor updates every time LTS Kernel (note: NOT LTSI here) is updated[2].

LTSI Development is a timing sensitive process just like Linux Kernel development. If you wish to work with LTSI it is very important to understand the development cycle of LTSI.


2. LTSI Development Process

Typically, new LTSI Kernels are released by the end of every year.

Before the release, there are a few steps developers are required /encouraged to go through. The followings are the descriptions of each steps.

New LTSI Version Announcement (May to September)

The Kernel version that will eventually become LTS/LTSI will be selected by Greg Kroah-Hartman and announced typically during May to September time frame (it varies every year depending upon the situation of the Kernel development). The announcement will be made through LTSI web site ( and LTSI Twitter account (@LinuxLTSI).

At the announcement, LTSI Project will provide the formal development schedule of the year.

Thus, developers are encouraged to start preparing for submitting patches to LTSI or even make sure to upstream the patches that they wish to back-port eventually to LTSI Kernel.

Merge Window Period (September to November)

Typically, LTSI Merge Window period starts from October and closes by the end of November. Developers are required to submit patches (new features, divers and fixes) to LTSI during this time period. Ideally all LTSI patches should come from later released kernel or at leased Linux-next tree to secure community review, however exceptions can be accepted if the patches are 1) beneficial to wide range of users, 2) projected to be upstreamed near future,

Validation Period (December)

LTSI formal new release requires a month of validation period. The Validation Period is typically during December time frame.

ALL developers who submitted patches are required to participate to this validation process, and fix their patches if there is anything happened.


3. LTSI Releases

Major LTSI Release:

Formal LTSI Release should be released once every year. Prior to the formal release, there will be a 2-month Merge Window and roughly one month of Validation Period following after the Merge Window close.

During the Merge Period, all developers are able to submit the patches they wish to be merged into LTSI Kernel. Preferably, all patches should come from newer kernel (=already verified in the community and merged) or at least staged at Linux-next (=review completed). However LTSI Project will still be able to consider approving the industry demanded patches that are not available in the upstream tree if they are judged by the LTSI Maintainer, Greg Kroah-Hartman, as reasonable enough to be merged.

After the merge window closed, no new features will be accepted to be merged. Developers are also encouraged to participate to the Validation Period during the one-month Testing Period.

 LTSI Maintenance Update (sync with every LTS migrations):

LTSI will be updated every time Greg Kroah-Hartman releases LTS in In case of 3.10 kernel, LTS release will be added sequence number of his update such as 3.10.25, 3.10.26, and 3.10.27. Greg will be re-basing LTSI kernel every time he releases LTS, thus there should be the LTSI Kernels that has the same version numbers as LTS such as LTSI-3.10.25, LTSI-3.10.26, LTSI-3.10.27.

If industry developer has other bug/security fix patches that are not available in the upstream, they can send such fixes to the LTSI tree via project mailing list.

Also, there will not be the tar-ball images provided by LTSI Project. Developers will have to pull the latest LTS kernel from the site and apply LTSI patches to create a complete LTSI kernel image by themselves.

 LTSI Maintenance Updated (Tar-ball):

Notwithstanding above, LTSI Project will provide a formal Updated tar-ball once every quarter. This release will require roughly 3 weeks of testing period prior to the release. Developers are encouraged to participate to this testing process.





[1] LTS (Long Term Stable) Kernel is the one normally, industry uses for their business. Majority of Linux distributions are, in fact, using LTS Kernel. While the kernel maintained by the Linux creator Linus Torvalds are only maintained for roughly 6 months, LTS kernels are maintained for 2 years.

[2] This minor update should only include security & bug fixes.