Genkernel/ja

genkernel というツールを使うと、kernelとinitramfsを自動的にビルドすることができます. その特徴を大まかに説明しますと：


 * Configuring the kernel sources;
 * Building the compressed kernel and copying it to
 * Creating an initramfs and copying it to
 * Creating symlinks in
 * Adding custom content to the initramfs such as encryption related files, boot splash images, extra modules, and more;
 * Compressing the initramfs;
 * Configuring the bootloader.

Emerge
genkernelのインストールを開始します:

使い方
genkernel を実行する際の一般的な文法は以下のとおり:

オプション
The actual behavior of genkernel depends on a large variety of options, the majority of which can be set/unset in the file or passed via the genkernel command on each invocation. Options passed over the command line take precedence over options defined in. The configuration file is very well documented, however some of the most commonly used options will be explored in this article. The goal is for the reader to be familiar with common genkernel invocations. For a more complete set of explanations refer to the comments in itself or to the output of the man genkernel command.

ユーザ対話型操作を提供するオプション
カーネルコンフィグレーションに関する下記のオプションは、コンフィグレーションの過程においてどのような対話型操作を提供するかを指定します. その過程の最中でも、ユーザはコンフィグファイルを保存するか否かを選択することができます. 以下が主なコンフィグレーションオプションです :

生成されるシステムに関するオプション
以下のコンフィグレーションオプションは、生成されるカーネルや initrd の仕様を左右します.

ビルドの際に使用されるツールを選択するためのオプション
次のオプションはgenkernelをすることによってサポートされており、カーネルを組み立てている間、関連するアプリケーションに渡されます. これらのオプションは、はるかに低いレベルではあるが、カーネルのコンパイル処理に使用するコンパイルツールに影響を与えます.

コンパイル手順に関するオプション
次のオプションは通常、実際のコンパイル時に有効になります:

デバッグ用オプション
カーネルのコンパイルプロセス中にデバッグオプションを使用すると、報告された情報の量だけでなく、言ったデータの表示を制御します.

アクション
The action passed on the command line with the genkernel [options …] action tells genkernel what action to perform. The following actions are supported:


 * all
 * Builds all stages — the initrd, kernel image and modules.


 * bzImage
 * Only builds the kernel image.


 * kernel
 * Only builds the kernel image and modules.


 * initramfs</tt>
 * Only builds the initramfs/ramdisk image.


 * ramdisk</tt>
 * Only builds the initramfs/ramdisk image.

Starting off
genkernelを実行する方法はいくつかありますが、ほとんどのユーザーに推奨最小侵襲アプローチは、genkernel all</tt>によって提供されています. ここでは、ほとんどのシステムに適しています一般的な構成が使用されます. 先に述べたように、このアプローチには欠点がないわけではありません. 作成されたモジュールのほとんどは、平均的なユーザーには役に立たないとコンパイル時間を増加させることができます. 以下は、rootとしてgenkernelをするために特定のオプションを渡すことによって達成より効率的な手法の説明図です.

The above operation causes genkernel to create a framebuffer splash-enabled kernel that will have to be manually installed. While preparing the kernel source tree, genkernel will refrain from cleaning out any preexisting object files present in the source tree. A menu-driven kernel configuration utility will be displayed that allows the user to select which modules will be built for the system.

Replacing  with the   option allows genkernel to automatically install the new kernel in the  directory, and will create symlinks if   is specified. Using the  option allows genkernel to mount the  partition automatically, if necessary.

カーネルの変更
The first thing that should be done is to allow the triggering of make menuconfig</tt> in the file:

ファイル管理
genkernelをを使用している間、ユーザーは、カーネルのコンフィギュレーションとカーネルイメージファイルの管理やカーネルソースは、システムによって処理される方法に関連するいくつかの側面を知っていなければなりません.

ソースファイル
After an emerge -u gentoo-sources</tt>, whenever new sources are available, a new kernel source directory is created under to host them. Normally, the active kernel sources directory is pointed to by the symlink.

The directory might look like this:

The symlink can be changed in different ways.


 * If the  USE is set the  symlink is automatically updated to point to the newly emerged sources.


 * If the  USE is not set, the user can change the destination of the symlink using the eselect kernel list</tt> followed by the eselect kernel set</tt> command.

genkernel will always (exclusively) use the sources pointed by the symlink.

カーネルコンフィグレーションファイル
If a kernel compilation has already been run with the active kernel sources, there might be a file inside the directory that contains the kernel configuration that has been applied while creating the last bzimage of the kernel. This file is named, for example where   might be substituted with the system's architecture,   might be substituted with the version of the sources used, and   with the release of the sources.

It is this file that is used as a starting configuration when running  genkernel --menuconfig all</tt>.

If it is the first time that genkernel is run with the new kernel sources, or if the previous result has not been saved, this file is substituted with a default configuration file that resides at where x86_64 is substituted with the actual architecture.

コンパイル済コンフィグレーションの保存
If the  genkernel option is activated, either from the command line or inside, the compiled kernel configuration is saved (with the name given above) into the  directory. At the same time, the configuration is saved in the file in  directory but this file is not reused on the next genkernel all</tt> run.

Installing the kernel and initramfs into the directory
Specifying the  option when invoking genkernel, will ask genkernel to install the kernel image and the initramfs into the  directory. In order to run  a convenient manner, set the following in the  file:


 * 最初のパラメータは、自身のために語っています.


 * The second parameter tells genkernel to save the compiled kernel configuration into


 * The last two options tell genkernel to automatically update the grub configuration. In practice, the following happens:
 * If a previous kernel image with the same name already exist, it is renamed by appending to its name. A symlink  is automatically created that points to it.
 * The new kernel takes the place of any kernel with the same name into . If it is the first time a kernel is compiled, a symlink kernel is automatically created that points to the new kernel.

After running genkernel --menuconfig all</tt>, the directory might look like this:

ブートローダの設定
新しいカーネルがブート可能でない場合であっても、そのようにブートローダの設定で上記のシンボリックリンクを使用することができ、ユーザーは常にブート古いものにすることができます.

To allow the kernel and intird provided by genkernel to run correctly, provide a minimum information in bootloader's configuration file :
 * Add  to the kernel parameters passed to the kernel image, where  points to the root partition.
 * If splash is used, add a suitable mode line such as  to the parameters passed to the kernel and also add   or   depending on the verboseness required through the boot process.
 * Add the initrd information as required by the bootloader. Consult the Bootloader Configuration Chapter of the Gentoo Handbook for details on how to make the bootloader initrd-aware.

Here is how the file might look.

作業ファイルの保存
genkernelのアプリケーションが自動的にファイルへの新しい変更を保存します. 以前の変更が保存される場合、次のアクションが取られる必要があります.


 * The first file to preserve is the kernel configuration file in If the source has not changed prior to the recompilation of the kernel, the previously used name for this file will be used. So copying the previous configuration file under a different name helps in preserving the information while keeping the file available as a starting point for a new configuration.


 * The second important thing is to preserve the already bootable kernel and initramfs images. The way to accomplish this depends on the context:
 * If the last kernel compiled is bootable, running genkernel will rename this kernel (and similarly initramfs) image to and create a new . This mean that even if the new kernel is not bootable, users will always be able to boot the old one.
 * If the last kernel compiled is not bootable and sources haven't changed since the user compiled a bootable one, prior to running genkernel, first delete the new kernel image and remove the .old</tt> suffix from the last bootable one. Without this, if the newly compiled kernel is not bootable for the second time, the bootable will be kicked out by the renaming of the non bootable, giving the user an unbootable system. Use the same reasoning for initramfs.

ソースを変更しながら、以前のカーネル設定を使用して
The previous configuration can be used through the  option in  as follows:

From an installation CD
The genkernel</tt> utility can build kernel and initrd images that provide support for network booting, or netbooting. With any luck, users should be able to netboot any recent computer into the environment provided by the Installation CD.

The magic lies in genkernel's linuxrc script: it will try to netmount the Installation CD using NFS. From there, the init scripts of the Installation CD can take over, as if the CD was present locally.

ネットブートをサポートしたカーネルとinitramfsを構築
To enable support for netbooting, include the following options while configuring the kernel:

First, the kernel image must include the drivers for the system's Network Interface Cards (NIC). Normally, drivers for such devices will be compiled as modules. However, it is essential (for netbooting) that such drivers are compiled directly into the kernel image and not as modules.

Be sure to select &lt;*&gt;</tt> and not &lt;M&gt;</tt>.

Secondly, it is suggested that IP: kernel level autoconfiguration is enabled as well as IP: DHCP support options. This avoids an unnecessary layer of complexity since the IP address and the NFS path to the Installation CD can be configured on a DHCP server. Of course, this means the kernel command line will remain constant for any machine — which is very important for etherbooting.

These options tell the kernel to send a DHCP request at bootup.

Additionally, enable SquashFS because most modern Gentoo Installation CDs require it. Support for SquashFS is not included with the generic kernel source tree. To enable SquashFS, apply the necessary patches to the generic kernel source or install gentoo-sources.

Once the compilation process is completed, create a compressed tarball (tar.gz) that contains the kernel's modules. This step is only necessary if the kernel version does not match the kernel image version on the Installation CD.

To create an archive containing all the modules:

Depending on the network boot mechanism, one of the following steps need to be followed:

To create an etherboot image:

To create a OpenBoot / SPARC64 TFTP image:

The file is the boot image.

Finally, copy this kernel to the TFTP server. The details are architecture-dependent and are beyond the scope of this guide. Please refer to the documentation for the specific platform of interest.

NFS setup
To setup a NFS share that contains the Installation CD, use the loop device to mount the ISO image and then copy the contents of the CD into the NFS share. As a nice extra, genkernel's initrd scripts will extract all tar.gz files located in the directory. All that needs to be done here is copy the archive to the  directory.

The following assumes that is an exported NFS share:

Now copy the file into :

DHCP setup
The netboot images will ask the DHCP server on the network for an IP as well as a  option. Both can be specified per host using a MAC address to identify machines:

Netbooting instructions
Netbooting itself is again very platform-specific. The important part is to specify the  and   parameters on the kernel command line, as this will bring up the network interface and tell the initrd scripts to mount the Installation CD via NFS. Here are some platform-specific tips.

For etherboot, insert the etherboot disk into the drive and reboot. The kernel command line was specified when the image was constructed. With Sparc64, hit - at the boot prompt and enter:

PXE のためには、pxelinux (syslinuxの一部)をセットアップし、 を作成して以下の行を続けます:

Introduction
If an initramfs is installed with genkernel, then take a look at the various boot options that can (or should) be defined in the bootloader configuration. The most common ones are added to this guide.

Loading LVM or software-RAID
If the system uses LVM or software-RAID, the initramfs has to be built using the  and   options. Do not forget to enable support during boot as well. This can be done using the dolvm and domdadm options.

Booting in single-user mode
If for some reason boot-up fails, rescuing the system by booting in the single-user mode is still possible. This will only load the really necessary services and then drop the user to a rescue (root) shell.

compile failed: Kernel not found
This failure can be experienced when attempting to compile a kernel for one architecture with a kernel file that has a target of a different architecture than the target. This could be as simple as a machine running an kernel attempting to compile for a  target.

This can be experienced when booting from a x86_64 livecd on a system that is capable of operating in 64-bits, however the target to be installed or repaired is 32-bits. After the compilation process begins, genkernel</tt> will attempt to automatically detect the architecture for the target based on the currently running kernel. If the currently running kernel is 64-bit, then, unless it is told otherwise, genkernel</tt> will presume it should be looking for a 64-bit kernel.

Suppose then that the kernel's file has x64 disabled. The <tt>make</tt> command will execute and the resulting kernel binary will be placed in the associated directory. When <tt>genkernel</tt> goes to install (move and rename) the kernel it cannot find the kernel because it expected a 64-bit kernel.

The solution to this failure is to set <tt>genkernel</tt>'s  option to, in this case, the  architecture. The final command could look like this:

To override the architecture choice permanently, modify the  variable in the  file.

参考

 * Manual kernel configuration - For the times it is necessary to to do things manually.
 * Dracut - Another initramfs builder available in Gentoo.