# Kernels/Compilation/Traditional

This article is an introduction to building custom kernels from kernel.org sources. This method of compiling kernels is the traditional method common to all distributions. If this seems too complicated, see some alternatives at: Kernels#Compilation

## Fetching source

- Fetch the kernel source from http://www.kernel.org. This can be done with GUI or text-based tools that utilize: HTTP, FTP, RSYNC, or Git.

For instance, using wget via http:

    $ wget -c https://www.kernel.org/pub/linux/kernel/v3.x/linux-3.10.4.tar.xz

- It is always a good idea to verify the signature for any downloaded tarball. See kernel.org/signature for how this works and other details.

- Copy the kernel source to your build directory, e.g.:

    $ cp linux-3.10.4.tar.xz ~/kernelbuild/

- Unpack it and enter the source directory:

    $ cd ~/kernelbuild
    $ tar -xvJf linux-3.10.4.tar.xz
    $ cd linux-3.10.4

Prepare for compilation by running the following command:

    make mrproper

This ensures that the kernel tree is absolutely clean. The kernel team recommends that this command be issued prior to each kernel compilation. Do not rely on the source tree being clean after un-tarring.

### What about /usr/src/ ?

Using `/usr/src/` for compilation as root, along with the creation of the corresponding symlink, has been the target of much debate.

- It is considered poor practice by some users. They consider the cleanest method to simply use your home directory for configuring and compiling. Then installing as root.

- Other experienced users consider the practice of the entire compiling process as root to be completely safe, acceptable, and even preferable.

Use whichever method you feel more comfortable with. The following instructions can be interchangeable for either method.

## Build configuration

This is the most crucial step in customizing the kernel to reflect your computer's precise specifications. By setting the options in `.config` properly, your kernel and computer will function most efficiently.

### Configure your kernel

Warning: If compiling the radeon driver into the kernel(>3.3.3) for early KMS with a newer video card, you must include the firmware files for your card. Otherwise acceleration will be crippled. See here
Tip: It is possible, to configure a kernel that does not require initramfs on simple configurations. Ensure that all your modules required for video/input/disks/fs are compiled into the kernel. As well as support for DEVTMPFS_MOUNT, TMPFS, AUTOFS4_FS at the very least. If in doubt, learn about these options and what they mean before attempting.

#### First-timers

Two options for beginners to ease use or save time:

- Copy the .config file from the running kernel, if you want to modify default Arch settings.

     $ zcat /proc/config.gz > .config

- localmodconfig Since kernel 2.6.32, this should only select those options which are currently being used.
  1. Boot into stock `-ARCH` kernel, and plug in all devices that you expect to use on the system.
  2. `cd` into your source directory and run: `$ make localmodconfig`
  3. The resulting configuration file will be written to `.config`. You can then compile and install as stated below.

#### Traditional menuconfig

`$ make menuconfig`

This will start with a fresh `.config`, unless one already exists (e.g. copied over). Option dependencies are automatically selected. And new options (i.e. with an older kernel `.config`) may or may not be automatically selected.

Make your changes to the kernel and save your config file. It is a good idea to make a backup copy outside the source directory, since you could be doing this multiple times until you get all the options right. If unsure, only change a few options between compiles. If you cannot boot your newly built kernel, see the list of necessary config items here. Running `$ lspci -k #` from liveCD lists names of kernel modules in use. Most importantly, you must maintain CGROUPS support. This is necessary for systemd.

#### Versioning

If you are compiling a kernel using your current config file, do not forget to rename your kernel version, or you may replace your existing one by mistake.

    $ make menuconfig
    General setup  --->
     (-ARCH) Local version - append to kernel release '3.n.n-RCn'

## Compilation and installation

### Compile

Compilation time will vary from 15 minutes to over an hour. This is largely based on how many options/modules are selected, as well as processor capability. See Makeflags for details.

Warning: If you use GRUB and still have LILO installed; `make all` will configure LILO, and may result in an unbootable system.

Run `$ make` .

### Install modules

    # make modules_install

This copies the compiled modules into `/lib/modules/[kernel version + CONFIG_LOCALVERSION]`. This way, modules can be kept separate from those used by other kernels on your machine.

### Copy kernel to /boot directory

    # cp -v arch/x86/boot/bzImage /boot/vmlinuz-YourKernelName

### Make initial RAM disk

If you do not know what this is, please see: Initramfs on Wikipedia and mkinitcpio.

    # mkinitcpio -k FullKernelName -c /etc/mkinitcpio.conf -g /boot/initramfs-YourKernelName.img

You are free to name the `/boot` files anything you want. However, using the [kernel-major-minor-revision] naming scheme helps to keep order if you:

- Keep multiple kernels
- Use mkinitcpio often
- Build third-party modules.

Tip: If rebuilding images often, it might be helpful to create a separate preset file resulting in the command being something like:`# mkinitcpio -p custom`. See here

If you are using LILO and it cannot communicate with the kernel device-mapper driver, you have to run `modprobe dm-mod` first.

### Copy System.map

The `System.map` file is not required for booting Linux. It is a type of "phone directory" list of functions in a particular build of a kernel. The `System.map` contains a list of kernel symbols (i.e function names, variable names etc) and their corresponding addresses. This "symbol-name to address mapping" is used by:

- Some processes like klogd, ksymoops etc
- By OOPS handler when information has to be dumped to the screen during a kernel crash (i.e info like in which function it has crashed).

Copy System.map to /boot, appending your kernel's name to the destination file. Then create a symlink /boot/System.map to point to /boot/System.map-YourKernelName.

    # cp System.map /boot/System.map-YourKernelName
    # ln -sf /boot/System.map-YourKernelName /boot/System.map

After completing all steps above, you should have the following 3 files and 1 soft symlink in your `/boot` directory along with any other previously existing files:

- Kernel: vmlinuz-YourKernelName
- Initramfs-YourKernelName.img
- System Map: System.map-YourKernelName
- System Map symlink: System.map

## Bootloader configuration

Add an entry for your amazing new kernel in your bootloader's configuration file - see GRUB, LILO, GRUB2 or Syslinux for examples.

Tip: Kernel sources include a script to automate the process for LILO: `$ arch/x86/boot/install.sh`. Remember to type `lilo` as root at the prompt to update it.

## Using the NVIDIA video driver with your custom kernel

To use the NVIDIA driver with your new custom kernel, see: How to install nVIDIA driver with custom kernel. You can also install nvidia drivers from AUR.

Category:

- Kernel