Ubuntu Wiki

Also refer to https://help.ubuntu.com/community/Kernel/Compile for building Ubuntu kernels.

Many times patches for bugs are committed upstream but have yet to make their way down to the Ubuntu kernel. It is often helpful if users are able to verify if the upstream patches do indeed resolve the issue they are witnessing. Likewise, in the opposite situation, it is useful to know if a bug may still exist upstream.

The following document should help users build their own kernel from the upstream mainline kernel to help verify if a bug still exists or not. If a bug is still present in the upstream kernel, it is encouraged that the bug be reported to http://bugzilla.kernel.org. The bug submission process is outlined at this page. Please note that the following steps are targeted towards Ubuntu users and focuses on building the mainline kernel from the git repository at http://git.kernel.org.

Prerequisites

There are a few tools that are necessary in order to build your own kernel(s). The 'git-core' package provides the git revision control system which will be used to clone the mainline git repository. The 'kernel-package' provides the make-kpkg utility which automatically build your kernel and generate the linux-image and linux-header .deb files which can be installed. You will need to install both of these packages.

sudo apt-get install git-core kernel-package fakeroot build-essential ncurses-dev

Note that, for newer versions of Ubuntu, you would replace "ncurses-dev" with "libncurses5-dev".

Kernel Build and Installation

1. Change to the directory where you want to clone the git tree. In this example we will use $HOME

   • cd $HOME

2. Clone the mainline kernel git tree.

   • git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

3. Change to linux directory.

   • cd linux

4. Copy the kernel config file from your existing system to the kernel tree.

   • cp /boot/config-`uname -r` .config

5. Bring the config file up to date. Answer any questions that get prompted. Unless you know you are interested in a particular feature, accepting the default option by pressing Enter should be a safe choice.

   • make oldconfig

   In cases where your kernel source is significantly newer than the existing config file, you'll be presented with all of the new config options for which there is no existing config file setting. You can either sit there and keep hitting Enter to take the default (generally safe), or you can just run

   • yes '' | make oldconfig

   which emulates exactly the same thing and saves you all that time.
6. (optional) If you need to make any kernel config changes, do the following and save your changes when prompted:

   • make menuconfig

   Note that Ubuntu kernels build with debugging information on, which makes the resulting kernel modules (*.ko files) much larger than they would otherwise be (linux-image*.deb will be 200-300 MB instead of 20-30 MB). To turn this off, go into "Kernel hacking"; then, under "Kernel debugging", turn OFF "Compile the kernel with debug info". Cf. bug 90283

7. Edit scripts/setlocalversion and comment out the line "echo "+"". If this is not done, make-kpkg will fail to build the packages with an error "package linux-image-[kernel version]-custom+ not in control info".

   • sed -rie 's/echo "\+"/#echo "\+"/' scripts/setlocalversion

   In addition, if you want to build from a git non-HEAD version, also comment out the lines extra plus at about line 168:

   • -       if test "${LOCALVERSION+set}" != "set"; then
     -               scm=$(scm_version --short)
     -               res="$res${scm:++}"
     -       fi
     +       #if test "${LOCALVERSION+set}" != "set"; then
     +       #       scm=$(scm_version --short)
     +       #       res="$res${scm:++}"
     +       #fi

   Cf. bug 58307

8. Clean the kernel source directory.

   • make-kpkg clean

9. Build the linux-image and linux-header .deb files (CONCURRENCY_LEVEL can also be set manually to how many CPUs/cores to use to build the kernel). This process takes a lot of time.

   • CONCURRENCY_LEVEL=`getconf _NPROCESSORS_ONLN` fakeroot make-kpkg --initrd --append-to-version=-custom kernel_image kernel_headers

   With this command the package names will be something like linux-image-2.6.24-rc5-custom and linux-headers-2.6.24-rc5-custom, and in that case the version will be 2.6.24-rc5-custom-10.00.Custom. You may change the string custom into something else by changing the --append-to-version option. You may also change the default 10.00.Custom into something else by using the --revision option.

10. Change to one directory level up (this is where the linux-image and linux-header .deb files were put)

    • cd ..

11. Now install the .deb files. In this example, the files are linux-image-2.6.24-rc5-custom_2.6.24-rc5-custom-10.00.Custom_i386.deb and linux-headers-2.6.24-rc5-custom_2.6.24-rc5-custom-10.00.Custom_i386.deb. You may receive warnings about '/lib/firmware/2.6.24-rc5-custom/' - this is expected and will only be problematic if the driver you are trying to test requires firmware.

    • sudo dpkg -i linux-image-2.6.24-rc5-custom_2.6.24-rc5-custom-10.00.Custom_i386.deb
      sudo dpkg -i linux-headers-2.6.24-rc5-custom_2.6.24-rc5-custom-10.00.Custom_i386.deb

12. You now need to make the new kernel bootable.
    • Get your module names.

      cd /lib/modules
      ls

      Update.

      sudo update-initramfs -ck module-name-for-new-kernel (in our case "update-initramfs -ck 2.6.24-rc5-custom_2.6.24-rc5-custom-10.00")
      sudo update-grub

13. You are now ready to boot into your new kernel. Just make sure you select the new kernel when you boot.

    • sudo reboot

Using Ubuntu Kernel Configuration

The basic instructions provided above work well if you are building your own custom kernel. However, if you want to build a kernel that matches the official Ubuntu kernel package configuration as much as possible a few extra steps are needed. Note that if you are simply trying to build the ubuntu kernel, you should be following the https://help.ubuntu.com/community/Kernel/Compile guide instead of this one.

1. Perform steps 1-7 above, use the Ubuntu kernel config in step 4
2. Override the kernel-package default packaging scripts with the Ubuntu packaging scripts:

   • cd $HOME
     git clone git://kernel.ubuntu.com/ubuntu/ubuntu-lucid.git
     cp -a /usr/share/kernel-package ubuntu-package
     cp ubuntu-lucid/debian/control-scripts/{postinst,postrm,preinst,prerm} ubuntu-package/pkg/image/
     cp ubuntu-lucid/debian/control-scripts/headers-postinst ubuntu-package/pkg/headers/

3. Build packages using overlay directory:

   • cd $HOME/linux
     CONCURRENCY_LEVEL=`getconf _NPROCESSORS_ONLN` fakeroot make-kpkg --initrd --append-to-version=-custom --overlay-dir=$HOME/ubuntu-package kernel_image kernel_headers

4. Perform steps 9-11 above

Note: The "--overlay-dir" option is only available in Lucid or later. If you need to build a kernel on a previous distribution, either install a backport of kernel-package if available, or manually edit /usr/share/kernel-package as needed.