From Fedora Project Wiki

Frequently asked questions about the kernel vanilla repositories for Fedora.

Contents

FAQ for users

What's the goal of these repositories?

The main ideas is to help upstream development, which in the end will benefit Fedora as well.

  • With the packages from the _kernel-vanilla-mainline_ repository it for example is quite easy to test kernels that are still under development. Bugs thus can be found early and reported and fixed upstream way before they enter a Linux kernel version shipped as a proper update in Fedora.
  • The kernels from the _kernel-vanilla-fedora_ repository make it easy to check if a bug that happens with a Fedora kernel is present upstream or caused by the patches the Fedora developers apply.
  • The kernels from the _kernel-vanilla-stable_ repository make it easy to check if a particular bug still happens with the latest stable kernel.

In general, these kernels make it easier to directly interact with upstream developers. That way users don't have to go through the sometimes overworked and quite busy developers that maintain the Linux kernel packages in Fedora.

Are the kernels from the kernel-vanilla repositories as good as those Fedora provides?

No. There are several reasons for why not; the most important ones:

  • the kernels shipped in the official Fedora repositories get a lot of testing. The kernels from the kernel vanilla repositories nearly no testing before uploaded to the repositories.
  • the official Fedora kernels sometimes contain changes that fix security problems or other crucial bugs before a fix gets merged in a official Linux kernel release.
  • the developers that take care of the kernel package in Fedora are far more experienced developers than those that take care of the kernel-vanilla repositories.

On the other hand using the kernels from the kernel-vanilla repositories should not be any more dangerous than downloading a Linux version from kernel.org and compiling and installing it source yourself.

Why so many repos? This looks stupid and over-engineered!

Yes, it might look over-engineered on the first sight, but allows us to serve different users bases. And once you look closer you'll notice that most of the time those four repositories contain only two Linux kernel versions per Fedora release.

Kernel.org frontpage on 2018-04-09

To explain this a bit more lets for example take a look April 9th, 2018. Back then…

  • Linux 4.16 was one week old and the first stable release 4.16.1 had just been released.
  • Linux 4.17 had one week into development, thus Linux 4.17-rc1 was still one week away.
  • Linux 4.15.x was still supported upstream and 4.15.16 had just been released.

At the same time…

  • Fedora 29 was prepared in Rawhide, which contained a mainline snapshot (4.17-pre-rc1).
  • Fedora 28 was in Beta and contained 4.16._x_.
  • Fedora 27 and 26 were the current releases and contained a Kernel based on Linux 4.15._x_.

In this particular point in time there were…

  • users that want the latest mainline snapshots (4.17-pre-rc1)
  • users that normally want the latest mainline snapshots, but want to avoid them during the busy merge window when most of the changes happen, as the risk of bad bugs is a bit bigger in those two weeks. Those users thus wanted the latest stable release (4.16._x_)
  • users that just wanted to use the latest Linux stable release (4.16._x_)
  • users that want to check if a problem they face with a Fedora kernel might be due to a patch that Fedora applied to their kernels (4.15._x_ for Fedora 27 and 26)
Kernel vanilla repositories on 20180409

And that's why there are four repositories, to serve each of those users what they want:

  • the _kernel-vanilla-mainline_ repo shipped a mainline snapshot (4.17-pre-rc1).
  • the _kernel-vanilla-mainline-wo-mergew_ repo shipped the latest stable release (4.16.1, but will jump to 4.17-rc1 once it's released).
  • the _kernel-vanilla-stable_ repo also shipped the latest stable release (4.16.1) (side note: the RPM packages are hardlinked to save space).
  • the _kernel-vanilla-fedora_ repo shipped a vanilla build of the kernel version that release is using; hence F29/rawhide had a mainline snapshot (4.17-pre-rc1), F28 had the lastest stable release (4.16.1) and F27 and F26 had the stable release from the previous version line (4.15.16).

Two or three weeks later F26 and F27 had made the jump to 4.16 and the merge window was over. Then the mainline and mainline-wo-mergew repo both shipped a 4.17 prerelease; the stable and the fedora repos both ship a 4.16.x kernel.

Can we trust the people behind it?

You have to decide yourself. If it is any help: Some of those that use or contribute to Fedora since a while will know that Thorsten has quite a history of Fedora contributions, even if he is very active in the past few years. You can assume he has no interest in ruin his reputation quickly by providing crappy packages in these repositories. On the other hand you should know that Thorsten started these repositories to dig deeper into the kernel and kernel development; so expect he'll make some mistakes along the way. And be reminded that using vanilla kernels has some known downsides and risks (see below).

Thorsten, do you use the vanilla kernels yourself?

Yes, I normally use the x86-64 vanilla kernels from the mainline-wo-mergew repository, either on the current Fedora release or the beta of the next one. But I don't reboot every day, so I might not boot each of the kernels in that repo.

Are the kernels safe to use?

That depends on your definition of 'safe'.

The Linux kernel is a complex piece of software and thus contains bugs. Those bugs lead to data loss a few times in the past; in very rare situations they even damaged hardware. Bugs like that often only show up under specific circumstances, as they otherwise likely would have been found and fixed already. Specific circumstances for example can be a specific mix of hardware used in combinations with a specific kernel version built with a particular set of configuration options. Nevertheless, in the end it unlikely that such a bug makes it into one of the non-development kernels from the kernel vanilla repositories, but there is still a very small chance fot that to happen.

Note that self compiled kernels bear exactly the same risk; chances of hitting serious bugs are lower for kernels that have undergone widespread testing already, as those found in the official Fedora repositories.

In other words: The kernels from the kernel-vanilla repositories will work just fine for most people. But use them on your own risk and have current backups at hand, as you always should.

Will everything work with the vanilla kernels that works with the official Fedora kernels?

No. Linux vanilla kernels are not that different from the kernels Fedora provides, but the latter include a few enhancements. Each was added for a good reason to make Fedora better, hence these improvements are missing when you use Linux vanilla kernels.

When this text was written in the spring of 2012, Fedora for example included utrace in their Linux kernels to support userspace tracing with Systemtap; hence this feature didn't work with the kernels from the kernel-vanilla repositories (but it should work these days, as Systemtap now uses a solution from the upstream kernel for its work).

Another example: The kernels from Fedora sometimes include fresher drivers which some systems will require to work properly.

Furthermore, in rare cases there are inter-dependencies between drivers in kernel and userland. The nouveau driver for graphics hardware from Nvidia was one such driver, as it had no stable API yet when this text was written; that's why the DRM/KMS driver in the kernel was marked as 'staging' back then. The Mesa 3D or X.org drivers included in a particular Fedora release therefore might depend exactly on the nouveau DRM/KMS driver shipped in the official Fedora kernel. In such cases the nouveau drivers for Mesa 3D and X.org of a certain Fedora release might not work properly with kernels found in the kernel-vanilla repositories, as their nouveau DRM/KMS driver might be newer or older and thus incompatible.

The non-development kernels found in the kernel-vanilla repositories therefore should work on a lot of systems, but on a few systems they might work slightly worse than the kernels Fedora provides.

Where to report bugs

If the Linux kernels in the packages from these repositories show any bugs please report them upstream to the Linux kernel developers, just as you would after installing a Linux kernel yourself using the sources available at kernel.org; that way all the bug reports go to the place where the people hang out that know how to fix them.

In case there are bugs in the packaging sent a mail to Thorsten Leemhuis (aka "knurd").

How can I avoid switching back and forth between vanilla kernels and Fedora kernels ?

Add 'exclude=kernel*' to the first section of these files in /etc/yum.repos.d/

fedora.repo fedora-updates.repo fedora-updates-testing.repo

Will this repository also ship updates userland components like drivers or udev that match the kernels in the repositories?

No, as there should be no need to, as the interfaces between the kernel and userland software should never change in incompatible ways; Linus Torvalds makes this pretty clear every so often.

That is the long story short. There are situations where the world is more complicated:

  • above mentioned rule does not apply to staging drivers, so situations might arise where the vanilla kernels are not usable for people that need staging drivers for their system.
  • Fedora sometimes might contain software that depends on bits that are not upstream.

And even with this rule sometimes a new mainline kernel versions brings changes that require updates userland software. Three examples:

  • the version number jump from 2.6.39 to 3.0 confused some software.
  • in rare cases fixing security problems was only possible my changing the interfaces in incompatible ways.
  • sometimes nobody notices early enough that interfaces have changed and reverting the change might break systems that already rely on the new behavior.

How we deal with them will be decided on a case by case basis. In some cases we might have to other solution then to add new versions of other software to the repositories. But the plan is to avoid this if possible.

Do you plan to provide packages for Longterm kernels

Unlikely. The main goal of the kernel vanilla repositories for Fedora is to help upstream kernel development; but Longterm kernels are a dead end and quite a bit away from mainline development, so they would not fit that well.

Using a Linux kernel version that is from an older version line than the one used by Fedora also increases the risk that something works worse, so it's possible to argue this idea most of the time doesn't make sense.

Additionally, the RPM packages shipped in these repositories normally have a higher version number then the kernel packages that Fedora ships with, thus Dnf automatically will prefer the kernel packages from this repo. Shipping older versions would only work for users that change the repositories definitions Fedora provides (fedora.repo; fedora-updates.repo, … – see above) to ignore all the kernels that Fedora ships in its repositories. That is not hard, but makes things more complicated.

Why are there no stable and mainline-wo-mergew repos for rawhide?

Those versions would be older than the ones used in Fedora rawhide. That is something we try to avoid for now (see above answer to "Do you plan to provide packages for longterm kernels" for details).

Do you plan to provide packages for "linux-next" or "linux-rt" as well?

For now: No. I know there is some interest in packages for them, but maintaining those will consume a lot of time regularly, and we have not enough resources to do it properly right now.

Get in contact if you think investing time in these areas makes sense.

Do you plan to provide vanilla kernels for RHEL and its derivatives?

Sounds like a good addition. But there are people more familiar with these distributions provide such packages already. It would mean additional work for us, too; and we currently have no one that would regularly run such kernels. So for now we won't get our feet wet in that area. But if you want to step up and help, get in contact.

What configuration do those kernels use?

The mainline kernels use basically the same configuration as the Fedora rawhide kernels. Maybe a few staging drivers might get turned on to help their development, but apart from it the plan is to stick closely to what Fedora does.

Why don't you put these kernels in Fedoras main repositories

The consensus in the Fedora project as far as we know is: That's not a good idea, as it divides the user base. It also would make the vanilla Linux kernels more 'official' and people might simply use those kernels without knowing what their downsides are.

That's the long story rough and short. And sure, there are reasons why having vanilla kernels in the main repositories would make sense. Feel free to start a discussion on the Fedora devel mailing list, we'll watch and might jump in.

Putting the kernels in a well know 3rd party add-on repository for Fedora might make sense, but some problems would be similar. It would also lead to more problems, as then users might ask said 3rd party repos to build add-on modules packages for those kernels, too.

The best approach would be to reduce the number of patches the Fedora kernel developers include for one reason or another down to zero or something very close to that. That would require changes not only in Fedora, but in the upstream workflow as well.

Are those kernels really unpatched?

Normally yes.

From time to time the packages but need to contain a handful of very small changes that are needed for packaging. Sometimes we also might be forced to temporary use patches to make the kernel build or usable for typical systems; this happens very rarely and fixes like these will normally head upstream quickly and hence vanish from the vanilla packages pretty soon again. Furthermore, this normally should only happen with mainline development kernels, not with stable kernels.

How up2date will those repositories be?

Most of the time they are quite up2date and only a day or two behind at max. But we do the work in our spare time. Sometimes the day job and this strange thing called 'real life' leave not much time to work on these kernels, which will lead to a bigger lag.

FAQ for contributors and developers

Can you please include the patch found at <URL>?

No. Get your patch merged upstream, then the change you are interested in will automatically show up in these packages. And even better: it will automatically get into Fedora and other distributions, too!

Is there a Git tree with the stuff used to build the SRPM somewhere?

Sure: http://fedorapeople.org/cgit/thl/public_git/kernel.git/. Kernels in the kernel-vanilla-mainline repository normally get build from the rawhide branch. Kernels in the kernel-vanilla-fedora repository are always built from the appropriate Fedora branch. Most of the time the kernels in the kernel-vanilla-stable repository come from here to, but sometimes they are build from the stabilization or transition branch.

Let us know if we should do modifications to allow others to contribute to or benefit from this git tree better.

Note: when using fedpkg with this dist.git repo you need to specify the Fedora release you are aiming for, for example like this: fedpkg --release f33. Additionally, the command sadly won't be able to download the files specified in the sources file if you clone the repo directly from the above URL. That's because fedpkg derives the download configuration for those files from the URL for the origin branch (specified in .git/config) and the reason why commands like fedpkg sources, fedpkg srpm, fedpkg prep or fedpkg local will fail.

To avoid this, you better add the repo as a remote to Fedora's official dist.git repo for the kernel, which the vanilla git repo is based on anyway:

git clone https://src.fedoraproject.org/rpms/kernel.git
git remote add vanilla git://fedorapeople.org/home/fedora/thl/public_git/kernel.git
git fetch vanilla
git checkout vanilla/rawhide-user-thl-vanilla-fedora

If you are struggling with this, feel free to get the vanilla dist.git repo like this (it uses a tricky workaround to make things work):

git clone https://thl.fedorapeople.org/rpms/kernel.git

Why are there no debug kernels and not even debuginfo packages

The space on repos.fedoraprople.org is limited, hence we need to limit the number of packages we can provide. The debuginfo packages are also quite big and thus downloading the koji results (for testing) and uploading the final repo would take a lot longer.

If you need the debuginfo packags consider rebuilding the SRPM with "rpmbuild -bb --with debuginfo" and installing the results. You can also rebuild the SRPM using "rpmbuild -bb --with dbgonly" in case you need a kernel image where all sorts of debug options are enabled in the configuration.

Let us know if there is interest in these packages, then maybe a solution can be found to provide these packages sooner or later.

Why don't you commit your changes to Fedora's kernel git repo on pkgs.fedoraproject.org?

That might make sense. But it bears the risk that a commit is done to a wrong branch and disturbs the work of the Fedora kernels maintainer. Further: Not all of those that contribute to Fedora can commit there. That's similar with the fedorapeople git repository, but the docs indicate others can be given access with the help of ACLs.

But whatever: Git is made for distributed development, so simply clone it and send pull requests if you have any additions.

Can I help?

Of course. Talk to Thorsten; best if you come with some ideas what you can and want to do.

Do you work together with the developers that maintain Fedora's kernel packages?

There is cooperation already. If you think more is needed in some areas let us know.

Please stop providing alternative kernel packages, they take attention away from the kernel packages Fedora provide and thus harm Fedora!

That's a valid concern, but we think the benefits outweigh the downsides.

That again that is the long story short. Just to get a little deeper into it and show a different view on the matter at hand: Similar arguments could be used to argue that Fedora should stop shipping patched kernels, as they take attention away from the upstream kernel. Up to a point such an argument is valid, too, but there are good reasons why Fedora patches its kernels.

Why did you drop the '-vanilla' postfix that normally gets added to the 'name' macro when you build Fedora's kernel RPM without patches locally?

I've thought about dropping or leaving it for a while, as both schemes have various benefits and downsides. In the end I went for dropping it due to reasons like this:

  • nearly every other repository in Fedoraland that ships variants of packages that are included in Fedora do not change the name.
  • the postfix in the name breaks some tools – for example things like 'fedpkg srpm' on the git checkout.
  • external solutions that heavily depend on the naming scheme Fedora uses (like the akmod/kmod stuff used in some external repositories) would break with the -vanilla postfix in the name.
  • DNF might not recognize kernel packages with a '-vanilla' postfix as 'installonly' and thus would perform a regular update for vanilla packages instead of installing them parallel to the current one.