How Linux Kernel Version Numbers Are Structured and What They Mean

Traditional Linux Kernel Version Control

When Linus first started kernel development, he used a simple incrementing variable starting from 0.x. At that time Linus was the sole developer, and this scheme was sufficient for recording and distributing new kernel releases.

Examples of early kernel versions are shown in the image below.

As more developers contributed and the number of revisions and patches grew, this scheme became inadequate. Starting with version 1.0, Linus adopted a new scheme with additional variables.

Introducing a More Descriptive Versioning System

In 1994, with the release of Linux 1.00, a new versioning system using three variables “abc” was introduced, where a, b, and c represent the major version, minor version, and revision number respectively.

For example, Linux 1.1.95 decodes to major 1, minor 1, and revision 95.

At that time, even minor numbers indicated stable releases, while odd numbers indicated development versions. Separate branches allowed developers to add and test new features without affecting the stable branch.

LTS kernels such as 3.2 were derived from stable 3.1, and development kernels like 3.3 branched from 3.2 to prepare for features in the upcoming 3.4.

Starting with Linux 2.4, a fourth variable was added to denote the patch version; e.g., 2.4.37.10 is the tenth patch of 2.4.37.

Patch version counts how many times the kernel has been updated after a patch, not the number of issues fixed.

This scheme persisted through Linux 2.6, but the growing length and complexity eventually required a new approach.

How Linux Kernel Versions Are Named Today

Since Linux 3.0, the fourth variable was removed, and the version format became “a.b.c”, where a is the major version, b the minor version, and c the revision count. This mirrors the scheme used between 1.0 and 2.4.

After the introduction of the new system, contributors could work on stable branches without risking the stable releases. Following the release of 4.0, the distinction between even (stable) and odd (development) minor numbers became unnecessary, and the first LTS in the 4.x series, 4.1, has an odd minor number.

Suffixes such as “rcX” indicate release‑candidate versions, which are preview builds for testing. At the time of writing, the latest preview is 5.19‑rc6.

When a variable reaches a certain threshold, the preceding variable increments; for example, when the minor count approaches 20, the major version increments.

Linus mentioned in his 5.0 kernel development mailing that he increased the major version to 5 because the minor count had become too large to count on fingers. Kernel.org notes that when the number after the first dot becomes “too large,” the major version is bumped. The final releases were 3.19 for the 3.x series, 4.20 for the 4.x series, and then 5.0.

Since version 3.0, this scheme has been consistently applied across the 3.x, 4.x, and 5.x series.

Identifying Linux Kernel Versions

Given the large number of released kernels, a systematic way to identify and compare versions is essential. The new versioning scheme makes it easy to determine which kernel is the latest and which are older.

To check the kernel version installed on a system, you can use the uname command, which displays system information; note that the output may differ from the actual kernel version depending on the distribution.