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 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).

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

Code Listing 4: 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 5: Selecting experimental code/drivers

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

Now, go to General Setup and since 2.6 is the default and only kernel supported on AMD64, we will
enable support for hot-pluggable devices for use with udev.

Code Listing 6: General Support

General setup --->[*] Support for hot-pluggable devices

We shall then select the exact processor type. The x86_64 kernel maintainer strongly recommends
users enable MCE features so that they are able to be notified of any hardware problems. On x86_64,
these errors are not printed to dmesg like on other architectures, but to /dev/mcelog. This requires
the app-admin/mcelog package.

Code Listing 7: Selecting processor type and features

Processor type and features  --->
   [ ] Intel MCE Features
   [ ] AMD MCE Features
  Processor family (AMD-Opteron/Athlon64)  --->
    ( ) AMD-Opteron/Athlon64
    ( ) Intel EM64T
    ( ) Generic-x86-64"

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 and /proc file system.

Code Listing 8: Selecting necessary file systems

File systems --->
  Pseudo Filesystems --->[*] /proc file system support[*] 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
  <*> JFS filesystem 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 9: 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.

If you have a multi-CPU Opteron or a multi-core (e.g. AMD64 X2) system, you should activate
"Symmetric multi-processing support":

Code Listing 10: Activating SMP support

Processor type and features --->[*] Symmetric multi-processing support

If you use USB Input Devices (like Keyboard or Mouse) don't forget to enable those as well:

Code Listing 11: Activating USB Support for Input Devices

Device Drivers --->
  USB Support --->
    <*>   USB Human Interface Device (full HID) support[*] HID input layer support

When you've finished configuring the 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 12: Compiling the kernel

# make && make modules_install

When the kernel has finished compiling, copy the kernel image to /boot. Use whatever name you feel
is appropriate for your kernel choice and remember it as you will need it later on when you
configure your bootloader. Remember to replace <kernel-version> with the name and version of your
kernel.

Code Listing 13: Installing the kernel

# cp arch/x86_64/boot/bzImage /boot/<kernel-version>

Now continue with Configuring 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 18: 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 19: Editing /etc/modules.autoload.d/kernel-2.6

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

Code Listing 20: /etc/modules.autoload.d/kernel-2.6

3c59x