= Building a custom kernel ''' [IMPORTANT] ====== This page was automatically converted from https://fedoraproject.org/wiki/Building_a_custom_kernel It is probably * Badly formatted * Missing graphics and tables that do not convert well from mediawiki * Out-of-date * In need of other love Please fix it, remove this notice, and then add to `_topic_map.yml` Pull requests accepted at https://pagure.io/fedora-docs/fedora-howto Once that is live, go to the original wiki page and add an `{{old}}` tag, followed by a note like .... {{admon/note|This page has a new home!| This wiki page is no longer maintained. Please find the up-to-date version at: https://docs.fedoraproject.org/whatever-the-url }} .... ====== ''' This document provides instructions for advanced users who want to rebuild the kernel from some source. Note, however, that when building or running any such kernel, one should NOT expect support from the Fedora kernel team; you're pretty much on your own here if something doesn't work as you'd hoped or expected. But hey, you're an advanced user, so you can handle it, right? Anyway, advanced users build custom kernels for a variety of reasons: * To apply patches for testing that they either generated or obtained from another source * To reconfigure the existing kernel * To learn more about the kernel and kernel development [[dependencies-for-building-kernels]] Dependencies for building kernels ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Not all of these will apply to all methods but this provides a good dependency list of items to install `# sudo dnf install fedpkg fedora-packager rpmdevtools ncurses-devel pesign` Give the following command from the top directory of the kernel source tree once you have checked it out `# sudo dnf builddep kernel.spec` if you plan to run 'make xconfig' `# sudo dnf install qt3-devel libXi-devel gcc-c++` Also make sure you add the user doing the build to /etc/pesign/users and run the authorize user script: `# sudo /usr/libexec/pesign/pesign-authorize-users` It should be noted that pesign pesign-rh-test-certs gets pulled in automatically for some, but not for everyone, it depends on how you installed pesign. It is best to make sure that you have it installed. [[building-a-kernel-from-the-fedora-source-tree]] Building a Kernel from the Fedora source tree ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Make sure you have installed all dependencies `$ fedpkg clone kernel` you will likely need to checkout the source anonymously unless you have an Fedora developer account `$ fedpkg clone -a kernel` As of the time of this wiki writing, the kernel is managed using git. Each fedora release is a separate branch. rawhide tracks master. To get the tree for a particular release, you can use git checkout from the top of your newly created source tree. e.g. for fedora 23, `$ git checkout origin/f23` You can now make whatever changes / customizations you need before generating the rpms and installing them. You may want to consider uncommenting `# define buildid .local` to avoid conflicts, e.g. `%define buildid .local` When finished, generate the appropriate rpms with `$ fedpkg local` The rpms will be generated in a subdirectory $ARCH which can then be installed: `$ dnf install --nogpgcheck ./x86_64/kernel-$version.rpm` [[building-a-non-debugging-kernel]] Building a non-debugging kernel ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Branched kernels are built with debugging enabled by default in the early stages of the release to assist developers. To make a kernel with debugging information disabled, you can follow the above instructions to check out and do: `$ make release` `$ fedpkg local` [[enabling-config-options]] Enabling config options ^^^^^^^^^^^^^^^^^^^^^^^ If there are configuration options that need to be adjusted for your build, you can add changes in the kernel-local file. These changes will get picked up when you build. [[updating]] Updating ^^^^^^^^ * `$ cd kernel` * `kernel $ git status` ** your tree will be dirty in the configs and kernel.spec * `kernel $ git stash` ** puts aside your changes so your tree will be clean * `kernel $ git pull origin` ** update to the latest tree from fedpkg git Now you can run whatever other commands you want (e.g. make release) [[building-a-kernel-from-the-exploded-git-trees]] Building a kernel from the exploded git trees ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Fedora keeps a git tree containing Fedora patches applied on top of the vanilla sources. `$ git clone `git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git[`git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git`] `$ git checkout -b my_branch kernel-4.7.4-200.fc24` You can now build the kernel following regular kernel instructions. This tree is useful for generating patches that can be applied to the kernel.spec. [[building-a-kernel-from-the-source-rpm]] Building a Kernel from the source RPM ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Instructions for this are on a link:Building_a_custom_kernel/Source_RPM[ separate page]. In general, you should use one of the other methods for building the kernel which are much easier. [[building-only-kernel-modules-out-of-tree-modules]] Building Only Kernel Modules (Out Of Tree Modules) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ This section is for users who are only interested in working on a kernel module, and who do not wish to build an entire custom kernel. It is not necessary to download and rebuild the entire kernel in order to build a module. To build a module for the currently running kernel, only the matching `kernel-devel` package is required. Run the following command to install the `kernel-devel` package using `dnf`. .... su -c 'dnf install kernel-devel' .... You can build against any kernel version, as long as you have `kernel` and `kernel-devel` packages installed for that version. The rest of this section assumes we're building for the running kernel; if not, replace `\`uname -r\`` with the desired version number. As a simple example, to build the `foo.ko` module from `foo.c`, create the following `Makefile` in the directory containing the `foo.c` file: .... obj-m := foo.o KDIR := /lib/modules/$(shell uname -r)/build PWD := $(shell pwd) default: [TAB]$(MAKE) -C $(KDIR) M=$(PWD) modules .... [TAB] Denotes a tab character which must come first for makefile lines containing commands. Then, issue the `make` command to build the `foo.ko` module. The above is a helpful local Makefile wrapper invoking kbuild; in general you can simply do things like .... # make -C /lib/modules/`uname -r`/build M=`pwd` modules # make -C /lib/modules/`uname -r`/build M=`pwd` clean # make -C /lib/modules/`uname -r`/build M=`pwd` modules_install .... etc to build those targets. [[building-vanilla-upstream-kernel]] Building Vanilla upstream kernel ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Sometimes a Fedora developer may ask you to try building and installing an upstream kernel (possibly with a patch added) for testing. If there are multiple iterations, it may be quicker for you to do this than for the developer to turn around several RPMs. [[existing-fedora-vanilla-packages]] Existing Fedora Vanilla packages ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ There is an effort underway for packaging vanilla kernels. link:Kernel_Vanilla_Repositories[ See if this meets your needs first] [[getting-the-sources]] Getting the sources ^^^^^^^^^^^^^^^^^^^ Clone a kernel tree from kernel.org `$ git clone `git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git[`git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git`] This will clone the entire upstream tree. This may take a while depending on your connection speed. (While the tree is syncing, why not take the time to update some steps on this wiki that are inevitably out of date?) `$ cd linux` Double check what baseline is being used and check out a new one if necessary: `$ git checkout v4.5.2` [[applying-patches]] Applying patches ^^^^^^^^^^^^^^^^ [[the-patch-method]] The patch method ++++++++++++++++ If you were asked to apply any patches by the developer, this is the stage at which we would do so. These would typically be applied using a command something like.. `$ cat ~/testpatch.diff | patch -p1` If you have to try multiple different patches individually, you can unapply the previous one after testing by adding -R on the end of the above command. [[the-git-method]] The git method ++++++++++++++ Most developers these days generate patches using git and you can use git to help apply patches. You can do: `$ git am -3 ` This will create a git commit of a single patch in your tree. [[configuring-the-kernel]] Configuring the kernel ^^^^^^^^^^^^^^^^^^^^^^ Chances are that the kernel you are running is older than the one you are about to configure. This means there will be new options. There are several possibilities here. * If the developer has pointed you at a specific config file to use, save it in the linux directory with the filename .config * You can take your existing .config file by using the command `cp /boot/config-\`uname -r\`* .config` When you run the next step, you'll be asked (potentially lots of) questions about all the new options. Just hitting return 'should' always pick the safe decision for each option. However, it's worth taking care and reading each option, as this isn't always the case, and they may introduce new features your distro isn't capable of running, which may result in a non-booting system. * FIXME how to grab a rawhide config With the config in place, you are now ready to move on to the next step. [[building-the-kernel]] Building the kernel ^^^^^^^^^^^^^^^^^^^ `$EDITOR Makefile` Change the EXTRAVERSION line to add something on the end. For example, if it reads "EXTRAVERSION = -rc5" change it to "EXTRAVERSION = -rc5-dave" (what you choose is only relevant for the final part of this procedure) `$ make oldconfig` `$ make bzImage` `$ make modules` (become root) `# make modules_install` `# make install` You have now built and installed a kernel. It will show up in the grub menu next time you reboot. [[rebuilding]] Rebuilding ^^^^^^^^^^ If you have been asked to try several different things, the procedure once you have already built the tree once is mostly the same. A `make clean` is recommended between builds. This will leave the .config in place, so you can skip that step above and proceed straight to the `make bzImage` part of the steps above. Because we installed ccache in the first step, subsequent builds may go a lot faster as the compiler hits files that haven't changed since the last time it built them. [[cleaning-up]] Cleaning up ^^^^^^^^^^^ Once you have tested the kernel, and you've booted back to one of your kernels installed from an RPM, you can clean up the files that the above procedure installed by becoming root, and calling these commands. (Be sure to get the kernel version correct!) Remember above, we changed EXTRAVERSION to add a 'tag' to the kernel ? All the files it installed will have this as part of the filename. So you should be able to use wildcards to delete them safely using commands similar to those below. (Just replace 'dave' with whatever tag you chose) .... rm -f /boot/config-2.6.*dave* /boot/initrd-2.6.*dave* /boot/vmlinuz-*dave* /boot/System.map-*dave* rm -rf /lib/modules/2.6*dave* .... Finally, you will need to remove the kernel as an option to your bootloader. This will change from architecture to architecture. For x86, (as root), edit /boot/grub2/grub.cfg or /boot/efi/EFI/fedora/grub.cfg if you have EFI enabled and delete the four lines relating to your kernel (They should be easy to spot, they'll be the ones with your tag). They'll look something like this.. .... title Fedora Core (2.6.22-rc3-dave) root (hd0,0) kernel /vmlinuz-2.6.22-rc3-dave ro root=/dev/md0 initrd /initrd-2.6.22-rc3-dave.img .... Category:Documentation Category:Tutorials ''' See a typo, something missing or out of date, or anything else which can be improved? Edit this document at https://pagure.io/fedora-docs/fedora-howto.