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7. Configuring the Kernel

Content:

7.a. Installing the Sources

Choosing a Kernel

The core around which all distributions are built is the Linux kernel. It is the layer between the user programs and your system hardware. Gentoo provides its users several possible kernel sources. A full listing with description is available at the Gentoo Kernel Guide.

For PPC64-based systems we have gentoo-sources (kernel source patched for extra features).

Choose your kernel source and install it using emerge.

Code Listing 1.1: Installing a kernel source

# emerge gentoo-sources

When you take a look in /usr/src you should see a symlink called linux pointing to your kernel source. In this case, the installed kernel source points to gentoo-sources-3.4.9. Your version may be different, so keep this in mind.

Code Listing 1.2: Viewing the kernel source symlink

# ls -l /usr/src/linux
lrwxrwxrwx   1 root   root      12 Oct 13 11:04 /usr/src/linux -> linux-3.4.9

Now it is time to configure and compile your kernel source. There is the ability to use genkernel which would create a generic kernel like the ones used on the installation CDs, but it is not fully functional for PPC64 at the moment.

Continue now with Manual Configuration.

7.b. Manual Configuration

Introduction

Manually configuring a kernel is often seen as the most difficult procedure a Linux user ever has to perform. Nothing is less true -- after configuring a couple of kernels you don't even remember that it was difficult ;)

However, one thing is true: you must know your system when you configuring a kernel manually. Most information can be gathered by emerging pciutils (emerge pciutils) which contains lspci. You will now be able to use lspci within the chrooted environment. You may safely ignore any pcilib warnings (like pcilib: cannot open /sys/bus/pci/devices) that lspci throws out. Alternatively, you can run lspci from a non-chrooted environment. The results are the same. You can also run lsmod to see what kernel modules the Installation CD uses (it might provide you with a nice hint on what to enable).

Code Listing 2.1: Invoking menuconfig

# cd /usr/src/linux
Important: In case you are in 32-bit userland, you must edit the top
level Makefile in /usr/src/linux and change the CROSS_COMPILE option to
CROSS_COMPILE ?= powerpc64-unknown-linux-gnu-. You must do this before you run
make menuconfig or it may result in kernel compilation problems.
# make menuconfig

You will be greeted with several configuration sections. We'll first list some options you must activate (otherwise Gentoo will not function, or not function properly without additional tweaks).

Activating Required Options

First go to File Systems and select support for the filesystems you use. Don't compile the file system you use for the root filesystem as module, otherwise your Gentoo system will not be able to mount your partition. Also select Virtual memory, /proc file system and /dev/pts file system for Unix98 PTYs:

Code Listing 2.2: Selecting necessary file systems

File systems --->
  [*] Virtual memory file system support (former shm fs)
  [*] /proc file system support
  [*] /dev/pts file system for Unix98 PTYs

(Select one or more of the following options as needed by your system)
  <*> Reiserfs support
  <*> Ext3 journalling file system support
  <*> JFS filesystem support
  <*> Second extended fs support
  <*> XFS filesystem support

Note: You will find some of the mentioned options under Pseudo filesystems which is a subpart of File systems.

If you are using PPPoE to connect to the Internet or you are using a dial-up modem, you will need the following options in the kernel (you will find the mentioned options under Networking support which is a subpart of Device Drivers):

Code Listing 2.3: Selecting PPPoE necessary drivers

Network device support --->
  <*> PPP (point-to-point protocol) support
  <*>   PPP support for async serial ports
  <*>   PPP support for sync tty ports

The two compression options won't harm but are not definitely needed, neither does the PPP over Ethernet option, that might only be used by ppp when configured to do kernel mode PPPoE.

If you require it, don't forget to include support in the kernel for your ethernet card.

Next select Maintain a devtmpfs file system to mount at /dev so that critical device files are already available early in the boot process.

Code Listing 2.4: Enabling devtmpfs support

Device Drivers --->
  Generic Driver Options --->
    [*] Maintain a devtmpfs filesystem to mount at /dev
    [ ]   Automount devtmpfs at /dev, after the kernel mounted the rootfs

When you're done configuring your kernel, continue with Compiling and Installing.

Compiling and Installing

Now that your kernel is configured, it is time to compile and install it. Exit the configuration and start the compilation process:

Code Listing 2.5: Compiling the kernel

(Apple/IBM)  # make && make modules_install

When the kernel has finished compiling, copy the kernel image to /boot.

Code Listing 2.6: Installing the kernel

(Apple/IBM)  # cp vmlinux /boot/kernel-3.4.9-gentoo

Now continue with Kernel Modules.

7.c. Kernel Modules

Configuring the Modules

You should list the modules you want automatically loaded in /etc/conf.d/modules. You can add extra options to the modules too if you want.

To view all available modules, run the following find command. Don't forget to substitute "<kernel version>" with the version of the kernel you just compiled:

Code Listing 3.1: Viewing all available modules

# find /lib/modules/<kernel version>/ -type f -iname '*.o' -or -iname '*.ko' | less

For instance, to automatically load the 3c59x.ko module (which is the driver for a specific 3Com network card family), edit the /etc/conf.d/modules file and enter the module name in it.

Code Listing 3.2: Editing /etc/conf.d/modules

# nano -w /etc/conf.d/modules
modules_2_6="3c59x"

Continue the installation with Configuring your System.


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Page updated December 17, 2013

Summary: The Linux kernel is the core of every distribution. This chapter explains how to configure your kernel.

Sven Vermeulen
Author

Grant Goodyear
Author

Roy Marples
Author

Daniel Robbins
Author

Chris Houser
Author

Jerry Alexandratos
Author

Seemant Kulleen
Gentoo x86 Developer

Tavis Ormandy
Gentoo Alpha Developer

Jason Huebel
Gentoo AMD64 Developer

Guy Martin
Gentoo HPPA developer

Pieter Van den Abeele
Gentoo PPC developer

Joe Kallar
Gentoo SPARC developer

John P. Davis
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Pierre-Henri Jondot
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Eric Stockbridge
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Rajiv Manglani
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Jungmin Seo
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Stoyan Zhekov
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Jared Hudson
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Colin Morey
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Carl Anderson
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Jack Morgan
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Erwin
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Joshua Saddler
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Gerald J. Normandin Jr.
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Donnie Berkholz
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Ken Nowack
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Lars Weiler
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Tobias Scherbaum
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