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7. Configuring the Kernel

Content:

7.a. Timezone

You first need to select your timezone so that your system knows where it is located. Look for your timezone in /usr/share/zoneinfo, then make a symlink to /etc/localtime using ln:

Code Listing 1.1: Setting the timezone information

# ls /usr/share/zoneinfo
(Suppose you want to use GMT)
# ln -sf /usr/share/zoneinfo/GMT /etc/localtime

7.b. 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 PPC you can choose between development-sources and gentoo-dev-sources (both 2.6 kernels). The latter is available when you perform a networkless installation. Beside those there is a special kernel-2.6-patchset for the Pegasos: pegasos-dev-sources. So let's continue with emerge'ing the kernel sources:

Code Listing 2.1: Installing a kernel source

# emerge gentoo-dev-sources

When you take a look in /usr/src you should see a symlink called linux pointing to your kernel source:

Code Listing 2.2: Viewing the kernel source symlink

# ls -l /usr/src/linux
lrwxrwxrwx    1 root     root           12 Jul 10 10:55 /usr/src/linux -> linux-2.6.9

If this isn't the case (i.e. the symlink points to a different kernel source) change the symlink before you continue:

Code Listing 2.3: Changing the kernel source symlink

# rm /usr/src/linux
# cd /usr/src
# ln -s linux-2.6.9 linux

Now it is time to configure and compile your kernel source. All architectures can use genkernel for this, which will build a generic kernel as used by the LiveCD. We explain the "manual" configuration first though, as it is the best way to optimize your environment.

Continue now with Manual Configuration.

7.c. 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 start configuring a kernel manually. Most information can be gathered by viewing the contents of /proc/pci (or by using lspci if available). You can also run lsmod to see what kernel modules the LiveCD uses (it might provide you with a nice hint on what to enable).

Now go to your kernel source directory and execute make menuconfig. This will fire up an ncurses-based configuration menu.

Code Listing 3.1: Invoking menuconfig

# cd /usr/src/linux
# 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 of all, activate the use of development and experimental code/drivers. You need this, otherwise some very important code/drivers won't show up:

Code Listing 3.2: Selecting experimental code/drivers

Code maturity level options --->
  [*] Prompt for development and/or incomplete code/drivers

Now go to File Systems and select support for the filesystems you use. Don't compile them as modules, otherwise your Gentoo system will not be able to mount your partitions. Also select Virtual memory, /proc file system:

Code Listing 3.3: Selecting necessary file systems

File systems --->
  Pseudo Filesystems --->
    [*] /proc file system support
    [ ] /dev file system support (OBSOLETE)
    [ ]   Automatically mount at boot
    [*] Virtual memory file system support (former shm fs)

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

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:

Code Listing 3.4: Selecting PPPoE necessary drivers

Device Drivers --->
  Networking 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 rp-pppoe when configured to do kernel mode PPPoE.

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

Disable ADB raw keycodes:

Code Listing 3.5: Disabling ADB raw keycodes

Macintosh Device Drivers --->
  [ ] Support for ADB raw keycodes

Also choose the correct RTC support (disable the Enhanced RTC option):

Code Listing 3.6: Activating the correct RTC option

Character devices --->
  [ ] Enhanced RTC

General setup --->
  [*] Support for /dev/rtc

Users of OldWorld machines will want HFS support so they can copy compiled kernels to the MacOS partition.

Code Listing 3.7: Activating HFS support

File Systems --->
  [*] HFS Support

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 run the commands which will compile the kernel:

Code Listing 3.8: Compiling the kernel

# make all && make modules_install

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

Code Listing 3.9: Installing the kernel

replace 2.6.9 with your kernel-version
(Apple/IBM)  # cp vmlinux /boot/kernel-2.6.9
(Pegasos)    # cp arch/ppc/boot/images/zImage.chrp /boot/kernel-2.6.9

Also don't forget to copy over the system map:

Code Listing 3.10: Copying the system map

# cp System.map /boot/System.map-2.6.9

It is also wise to copy over your kernel configuration file to /boot, just in case :)

Code Listing 3.11: Backing up your kernel configuration

# cp .config /boot/config-2.6.9

Now continue with Installing Separate Kernel Modules.

7.d. Installing Separate Kernel Modules

Configuring the Modules

You should list the modules you want automatically loaded in /etc/modules.autoload.d/kernel-2.6. 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 4.1: Viewing all available modules

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

For instance, to automatically load the 3c59x.o module, edit the kernel-2.6 file and enter the module name in it.

Code Listing 4.2: Editing /etc/modules.autoload.d/kernel-2.6

# nano -w /etc/modules.autoload.d/kernel-2.6

Code Listing 4.3: /etc/modules.autoload.d/kernel-2.6

3c59x

Now run modules-update to commit your changes to the /etc/modules.conf file:

Code Listing 4.4: Running modules-update

# modules-update

Since 2004.3 we suggest people to use udev in stead of devfs. To ensure your system works with it you need to emerge udev.

Code Listing 4.5: Emerging udev

# emerge udev

Continue the installation with Configuring your System.


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Page updated January 4, 2005

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

Sven Vermeulen
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
Editor

Pierre-Henri Jondot
Editor

Eric Stockbridge
Editor

Rajiv Manglani
Editor

Jungmin Seo
Editor

Stoyan Zhekov
Editor

Jared Hudson
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Colin Morey
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Jorge Paulo
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Carl Anderson
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Jon Portnoy
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Zack Gilburd
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Jack Morgan
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Benny Chuang
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Erwin
Editor

Joshua Kinard
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Tobias Scherbaum
Editor

Lars Weiler
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Jochen Maes
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Grant Goodyear
Reviewer

Gerald J. Normandin Jr.
Reviewer

Donnie Berkholz
Reviewer

Ken Nowack
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