Understanding SUSE Kernels & Flavours: 2025 Complete Guide

📖 The Context

During testing on openSUSE Leap 16, I discovered SUSE's 5 kernel repositories. Between upstream (kernel.org) and downstream (SUSE), a critical distinction that few understand.

This article demystifies openSUSE kernels: how openSUSE selects them, how you can choose them, and why this decision transforms your experience on each flavor.

An essential guide for 2025.

🚀 Quick Start (For Those in a Hurry)

Which kernel to choose? (Quick decision)

Your Situation	Recommended Kernel	Reason
On Tumbleweed/MicroOS/Kalpa/Aeon	Official	Optimized, tested, stable
On Leap 16	Official	LTS guaranteed 24 months
On Leap 15.6	🚀 Migrate to Leap 16	EOL support December 2025
Testing new hardware	Kernel:HEAD	Article 2 for procedure
Debugging a bug	Kernel:vanilla	Article 3 for methodology

🏛️ FUNDAMENTALS: Linux Kernel Branches (kernel.org)

🔍 Understanding the 6 Key Concepts

To understand SUSE Kernels, first analyze Linus Torvalds' concept:

Mainline

Mainline = Linus Torvalds' main development branch

Contains all new features
Potentially unstable
Each new major version: v6.17 → v6.18 → v6.19
Short support after release (defined by kernel.org)

Stable

Stable = Stabilized version of Mainline with fixes

More stable than Mainline
Receives bug fixes AND security updates
Variable duration depending on activity (check kernel.org)
EOL = end of updates for this version

Longterm / LTS

Longterm (LTS) = Official long-term support

Designated "LTS" by kernel.org (example: 6.12 LTS)
Receives ONLY security fixes (no new features)
Each LTS has precise EOL date published by kernel.org

RC (Release Candidate)

RC = "Release candidate" version

Not yet stable (may have bugs)
Allows testers to find issues
Example: 6.18-rc1, 6.18-rc2, 6.18-rc3 → then v6.18 stable

EOL

EOL (End Of Life) = Date when kernel.org stops updates

After EOL: no more upstream security fixes
For Stable: quick EOL
For LTS: EOL at long date (check kernel.org for exact dates)

linux-next

linux-next = Merge of all future subsystems

Aggregates code from all kernel developers
Preview of next major kernel (1+ years before release)
VERY unstable: often doesn't boot
Intended ONLY for kernel developers
No support, no defined EOL

🎓 The Metaphor Explained

👨‍💼

linux-next

Director (creates everything, depends on no one)

👨‍🏫

Mainline

Teacher (works with Director, produces RCs)

👨‍🎓

Stable

Students (become mature, support production)

🚪

EOL

Students who leave (end of studies, no more support)

🏫

LTS

Great Schools (continue long, long support)

📊 Kernel Branches Hierarchy Diagram

LINUX-NEXT

(The Director - Future)

next-20251028 (latest date)
Aggregates ALL future subsystems
Depends on NO ONE
Dev kernel only

↓

(creates)

MAINLINE

(The Teacher - Development)

v6.18-rc1 → v6.18-rc2 → v6.18-rc3
Depends on: linux-next
Produces: RC (Release Candidates)
When mature → becomes STABLE

↓

(becomes)

STABLE

(The Students - Short-term Production)

v6.17.5 (latest)
v6.17.4, v6.17.3, v6.17.2, v6.17.1, v6.17.0
Depends on: Mainline
Produces: Patches (6.17.x)
Support: Variable (few months)

When mature → binary choice:

↙

↘

EOL

(The Students Who Leave)

v6.16.12 [EOL]
Depends: Stable
Support: END
No patches

LTS

(Great Schools)

v6.12.55 (latest)
v6.12.54, 6.12.53...
Depends: Stable
Support: 2-6 years
Security only

📊 Summary Table

Concept	Type	Updates	Support	Users
Mainline	Development	Features + Security	Short	Dev, testers
Stable	Production	Bugs + Security	Variable	Production
LTS	Production	Security only	Long term	Stable production
RC	Test	Critical bugs	Temporary	Testers
EOL	Marker	None	Stop point	N/A
linux-next	Experimental	Merge all subsystems	None	Kernel dev only

Official source for dates: https://kernel.org and https://endoflife.date/linux

🎯 PART 1: openSUSE KERNEL REPOSITORIES

The 5 OBS Branches: What Are They For?

openSUSE maintains 5 different kernel repositories in OBS (Open Build Service). Each has a specific purpose, stability level, and target audience.

📊 Overview: The 5 Repositories

Repository	Version	openSUSE Patches	Stability	Usage	Audience	Flavor
Official	6.17 (TW) 6.12 LTS (Leap)	✅ Yes	⭐⭐⭐⭐⭐	Standard production	Everyone	All
Kernel:stable	6.17.5	✅ Yes	⭐⭐⭐⭐⭐	Fast updates	Advanced	TW/MicroOS/Kalpa/Aeon
Kernel:HEAD	6.18-rc3	✅ Yes	⭐⭐⭐	Future kernel testing	Testers	TW/MicroOS/Kalpa/Aeon
Kernel:vanilla	6.18-rc3	❌ No	⭐⭐⭐	Debugging	Experts	All
Kernel:linux-next	next-20251027	❌ No	⭐	Kernel dev	Dev only	❌ No one

1️⃣ Official (Default)

This is your current kernel. The best for 99% of cases.

Aspect	Detail
What it is	Optimized and tested openSUSE kernel
openSUSE Patches	✅ Yes (Btrfs, KVM, security)
Tested	✅ Via openQA (quality tests)
Support	✅ Officially guaranteed by SUSE
For whom	All users
Use case	Production, daily use
Recommendation	✅ Keep it, don't change

Characteristics:

Tested before each openSUSE release
Full support guaranteed by SUSE
Patches optimized for performance and security
Complete Btrfs, KVM/Xen integration

2️⃣ Kernel:stable

For users wanting even faster updates.

Aspect	Detail
What it is	kernel.org stable kernel + openSUSE patches
openSUSE Patches	✅ Yes (same as Official)
Difference from Official	Updates 2-3 days before Official
Stability	⭐⭐⭐⭐⭐ (kernel.org stable)
For whom	Advanced users
Use case	Fast access to updates
On Leap	⚠️ Useless (Leap favors LTS)

When to use it:

Tumbleweed/MicroOS/Kalpa/Aeon
You want faster updates
You accept testing earlier

3️⃣ Kernel:HEAD

Tumbleweed's future kernel in Release Candidate (RC).

Aspect	Detail
What it is	Future Tumbleweed kernel in testing
Version	6.18-rc3 (not yet stable)
openSUSE Patches	✅ Yes
Stability	⭐⭐⭐ (RC = unstable)
Risk	⚠️ Medium (may not boot)
For whom	Testers, contributors
Use case	Testing, new hardware
On Leap	❌ Not recommended

When to use it:

Tumbleweed/MicroOS/Kalpa/Aeon only
Testing new hardware (recent GPU, CPU)
Contributing to openSUSE testing
You accept the risks

📖 Read Article 2 for secure installation procedure

4️⃣ Kernel:vanilla

100% mainline Linux kernel, WITHOUT openSUSE patches.

Aspect	Detail
What it is	Pure kernel.org kernel
Version	Mainline or LTS (depending on need)
openSUSE Patches	❌ None (pure kernel.org)
Stability	⭐⭐⭐ (depends on mainline)
Risk	⚠️ Medium
For whom	Experts, developers
Use case	Debugging only

When to use it:

Isolate bugs: Is it an openSUSE bug or kernel.org bug?
Methodical debugging: Compare vanilla vs Official behavior
Experts only: Return to Official after debug

📖 Read Article 3 for debugging methodology

5️⃣ Kernel:linux-next

Future major kernel code. VERY unstable.

Aspect	Detail
What it is	Merge of all future subsystems
Version	next-YYYYMMDD
Stability	⭐ (very low)
Risk	🔴 Very high (rarely bootable)
For whom	Kernel developers only
Use case	Future kernel development

When to use it:

❌ NEVER in normal usage
Kernel developers only
Testing long before stable release

📊 Decision Table: Which Repository For You?

If you're on Tumbleweed / MicroOS / Kalpa / Aeon

Your Need	Repository	Reason
No idea, normal usage	✅ Official	Optimized, tested, stable
Faster updates	✅ Kernel:stable	2-3 days before Official
Testing future kernel	⚠️ Kernel:HEAD	For tests, new hardware
Debugging a problem	🔍 Kernel:vanilla	Isolate bugs
Kernel development	🔴 linux-next	Experts only

If you're on Leap 16 / Leap Micro 6.2 / Slowroll

Your Need	Repository	Reason
No idea, normal usage	✅ Official	LTS optimized, tested, stable
More frequent LTS updates	✅ Kernel:longterm	Same stability, fast updates
Debugging a problem	🔍 Kernel:vanilla	Isolate bugs
HEAD or linux-next	❌ Not recommended	Leap = stability, not RC testing

If you're on Leap 15.6

Your Need	Repository	Reason
Short term	Official	Kernel 6.4 maintained until Dec 2025
Debugging	🔍 Kernel:vanilla	Isolate bugs
Recommended	🚀 Migrate to Leap 16	Support until Oct 2027

🔧 PART 2: ORIENTATION

Identify Your Configuration

Before choosing, see what you have:

# Your current kernel

uname -r

# Examples:

# 6.17.4-1-default         → Tumbleweed/MicroOS/Kalpa/Aeon

# 6.12.7-1-default         → Leap 16 / Slowroll / Leap Micro 6.2

# 6.4.0-150600.23-default  → Leap 15.6

# Your flavor

cat /etc/os-release | grep PRETTY_NAME

Interpreting the result:

6.17.4-1-default

│    │ │

│    │ └─ "default" = official kernel

│    └─── "1" = openSUSE Patch

└─────── "6.17.4" = Kernel version

🏗️ openSUSE Flavors: Overview

🌀

Tumbleweed

~6.17

Type: Rolling
Stability: ⭐⭐⭐⭐
Usage: Agile Desktop/Server

🛡️

Leap 16

6.12 LTS

Type: Stable
Stability: ⭐⭐⭐⭐⭐
Usage: Production

📜

Leap 15.6

6.4 (SUSE)

Type: Legacy
Stability: ⭐⭐⭐⭐⭐
Usage: ⚠️ EOL Dec 2025

🐌

Slowroll

~6.12 LT

Type: Slow rolling
Stability: ⭐⭐⭐⭐⭐
Usage: Stable desktop

📦

MicroOS

~6.17 (TW)

Type: Immutable
Stability: ⭐⭐⭐⭐
Usage: Servers

🎨

Kalpa

~6.17 (TW)

Type: Immutable KDE
Stability: ⭐⭐⭐⭐
Usage: Immutable desktop

🔧

Aeon

~6.17 (TW)

Type: Immutable GNOME
Stability: ⭐⭐⭐⭐
Usage: Immutable desktop

🌐

Leap Micro 6.2

6.12 LTS

Type: Immutable
Stability: ⭐⭐⭐⭐⭐
Usage: Edge/Containers

⚠️ PART 3: KEY CONCEPTS

CRITICAL: Upstream vs Downstream

The most important concept for understanding openSUSE kernel support.

The Two Support Levels: Explanatory Table

Aspect	Upstream Support (kernel.org)	Downstream Support (SUSE/openSUSE)
What it is	Official Linux source code	Distribution maintenance
Who maintains	Greg Kroah-Hartman and team	SUSE/openSUSE
How long	2-6 years depending on LTS	Until distribution end
After upstream EOL	❌ No more updates	✅ SUSE continues maintenance
Patches	Published by kernel.org	Applied by SUSE
EOL dates	Strict, defined	Flexible, tied to distribution

Key point: Upstream EOL ≠ Your distribution EOL

Concrete Example: Leap 16

Leap 16 Timeline with Kernel 6.12 LTS:

Oct 2025          Dec 2026           Oct 2027

│                 │                  │

├─────────────────┤──────────────────┤

│ Upstream active │ Downstream SUSE  │

│ (kernel.org)    │ (SUSE only)      │

└─────────────────┴──────────────────┘

        Leap 16 Support: 24 months

✅ You are protected for the ENTIRE duration of Leap 16

📊 Support and Lifecycles

Support Durations by Flavor

Flavor	Support	Release	End Support
Leap 16	24 months	Oct 2025	Oct 2027
Leap 15.6	18 months	Jun 2024	⚠️ Dec 2025
Tumbleweed	Rolling	-	Continuous
Slowroll	Rolling	-	Continuous
MicroOS/Kalpa/Aeon	Rolling	-	Continuous
Leap Micro 6.2	24 months	Oct 2025	Oct 2027

⏰ Countdown - Leap 15.6 Support End

Days remaining until Leap 15.6 support ends

LTS Kernels: Upstream EOL Dates

⚠️ These dates = upstream support. SUSE may maintain longer. Minimum guaranteed is indicated; support may be extended.

Kernel	Release	Upstream EOL	Minimum Duration
6.12 LTS	Nov 2024	Dec 31 2026	~2 years
6.6 LTS	Oct 2023	Dec 31 2026	~3 years
6.1 LTS	Dec 2022	Dec 31 2027	5 years
5.15 LTS	Oct 2021	Oct 31 2026	5 years
5.10 LTS	Dec 2020	Dec 31 2026	6 years

Sources: https://kernel.org | https://endoflife.date/linux

Practical Cases: Support Comparison

Event	Leap 16 + Kernel 6.12	Leap 15.6 + Kernel 6.4
Kernel release	Nov 2024	Jun 2023
Upstream EOL	Dec 2026	Sept 2023 (3 months!)
Distribution release	Oct 2025	Jun 2024 (kernel already EOL!)
Active upstream support	Nov 2024 → Dec 2026	❌ Never (EOL before release)
Downstream support	Dec 2026 → Oct 2027	Jun 2024 → Dec 2025
End all support	Oct 2027	⚠️ Dec 2025 (soon!)
Total duration	✅ 24 months protected	⚠️ 18 months, then no support
Action	✅ Stable until 2027	🚀 Migrate to Leap 16 before Dec 2025

❓ PART 4: FAQ

Upstream vs Downstream?

Upstream = kernel.org. Downstream = SUSE maintains after upstream EOL.

Which repository to choose?

Official for 99%. Stable for advanced TW. HEAD/vanilla for tests/debug.

Leap 16 supported how long?

24 months (Oct 2025 → Oct 2027). Kernel 6.12 maintained by SUSE for 24 months.

Kernel 6.12 EOL when?

Upstream: Dec 2026. Downstream SUSE for Leap 16: Oct 2027.

Stay on Official?

✅ Yes for 99% of cases. Support guaranteed by SUSE.

Leap 15.6 → Leap 16?

Strongly recommended before Dec 2025. Kernel 6.4 upstream support EOL Sept 2023.

Which flavor to choose?

Tumbleweed = agile. Leap = production. Slowroll = compromise.

Slowroll = which kernel?

~6.12 longterm.

MicroOS kernel?

Follows Tumbleweed (~6.17).

Kalpa vs Aeon?

Kalpa = KDE. Aeon = GNOME. Same kernel (~6.17).

✅ PART 5: SUMMARY

Key Points

Point	Detail
The 5 repositories	Official, stable, HEAD, vanilla, linux-next
Official = best	Guaranteed support, optimized patches, tested
Two support levels	Upstream (kernel.org) ≠ Downstream (SUSE)
SUSE protects after EOL	Leap 16: 24 months even if upstream EOL before
6.12 LTS EOL	Upstream: Dec 2026 (~2 years minimum)
6.4 NEVER LTS	Upstream EOL Sept 2023
Migration 15.6	Before Dec 2025 → Leap 16

🎯 Conclusion

Keep the Official kernel of your flavor. SUSE maintains for the entire distribution lifetime, even after upstream EOL.

By Flavor

Tumbleweed → ~6.17 (rolling, continuous support)
Leap 16 → 6.12 LTS (24 months, Oct 2027)
Leap 15.6 → 6.4 (Dec 2025) ⚠️ Migrate before this date
Slowroll → ~6.12 longterm
MicroOS/Kalpa/Aeon → ~6.17 (follows Tumbleweed)
Leap Micro 6.2 → 6.12 LTS (24 months)

The critical distinction: Upstream (kernel.org) vs Downstream (SUSE)

You are protected by SUSE even after upstream EOL.

📚 Next Steps

Need	Article	Duration
Test Kernel:HEAD	Article 2: Secure Installation	10-12 min
Debug problem	Article 3: Kernel Debugging	12-14 min
Understand basics	✅ Article 1 completed	-