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7. Configuring the Kernel
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:
Koodilistaus 1.1: Setting the timezone information
# ls /usr/share/zoneinfo
# 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
For AMD64-based systems we have gentoo-sources (kernel v2.6 source
patched with amd64 specific fixes for stability, performance and hardware
Choose your kernel source and install it using emerge.
Running emerge gentoo-sources will fail due to a bug with the Universal
Installation CD. Please make sure you run emerge
=gentoo-sources-2.6.11-r1 instead. This has no further effect on your
environment as Portage will automatically download a more recent kernel source
when updating your system (after the installation).
Koodilistaus 2.1: Installing a kernel source
# echo "=sys-kernel/gentoo-sources-2.6.11-r1 ~amd64" >> /etc/portage/package.keywords
# emerge =gentoo-sources-2.6.11-r1
When you take a look in /usr/src you should see a symlink called
linux pointing to your kernel source:
Koodilistaus 2.2: Viewing the kernel source symlink
# ls -l /usr/src/linux
lrwxrwxrwx 1 root root 12 Oct 13 11:04 /usr/src/linux -> linux-2.6.11-gentoo-r1
If this isn't the case (i.e. the symlink points to a different kernel source)
change the symlink before you continue:
Koodilistaus 2.3: Changing the kernel source symlink
# rm /usr/src/linux
# cd /usr/src
# ln -s linux-2.6.11-gentoo-r1 linux
Now it is time to configure and compile your kernel source.
You can use genkernel for this, which will build a generic kernel as used
by the Installation CD. We explain the "manual" configuration first though, as
it is the best way to optimize your environment.
If you want to manually configure your kernel, continue now with Default: Manual Configuration. If you want to use
genkernel you should read Alternative: Using
7.c. Default: Manual Configuration
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.
Koodilistaus 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:
Koodilistaus 3.2: Selecting experimental code/drivers, General setup
Code maturity level options --->
[*] Prompt for development and/or incomplete code/drivers
General setup --->
[*] Support for hot-pluggable devices
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. Do not select /dev file system since 2005.0/AMD64
uses udev by default.
Koodilistaus 3.3: Selecting necessary file systems
File systems --->
Pseudo Filesystems --->
<*> /proc file system support
< > /dev file system support (OBSOLETE)
<*> Virtual memory file system support (former shm fs)
<*> 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:
Koodilistaus 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
If you have a multi-CPU Opteron system, you should activate "Symmetric
Koodilistaus 3.5: 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:
Koodilistaus 3.6: 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:
Koodilistaus 3.7: Compiling the kernel
# make && make modules_install
When the kernel has finished compiling, copy the kernel image to
Koodilistaus 3.8: Installing the kernel
# cp arch/x86_64/boot/bzImage /boot/kernel-2.6.11-gentoo-r1
It is also wise to copy over your kernel configuration file to
/boot, just in case :)
Koodilistaus 3.9: Backing up your kernel configuration
# cp .config /boot/config-2.6.11-gentoo-r1
Now continue with Configuring Kernel
7.d. Alternative: Using genkernel
If you are reading this section, you have chosen to use our genkernel
script to configure your kernel for you.
Now that your kernel source tree is installed, it's now time to compile your
kernel by using our genkernel script to automatically build a kernel for
you. genkernel works by configuring a kernel nearly identically to the
way our Installation CD kernel is configured. This means that when you use
genkernel to build your kernel, your system will generally detect all
your hardware at boot-time, just like our Installation CD does. Because
genkernel doesn't require any manual kernel configuration, it is an ideal
solution for those users who may not be comfortable compiling their own kernels.
Now, let's see how to use genkernel. First, emerge the genkernel ebuild:
Koodilistaus 4.1: Emerging genkernel
# emerge genkernel
Now, compile your kernel sources by running genkernel all.
Be aware though, as genkernel compiles a kernel that supports almost all
hardware, this compilation will take quite a while to finish!
Note that, if your boot partition doesn't use ext2 or ext3 as filesystem you
need to manually configure your kernel using genkernel --menuconfig all
and add support for your filesystem in the kernel (i.e. not as a
Koodilistaus 4.2: Running genkernel
# genkernel all
Once genkernel completes, a kernel, full set of modules and
initial root disk (initrd) will be created. We will use the kernel
and initrd when configuring a boot loader later in this document. Write
down the names of the kernel and initrd as you will need it when writing
the bootloader configuration file. The initrd will be started immediately after
booting to perform hardware autodetection (just like on the Installation CD)
before your "real" system starts up.
Koodilistaus 4.3: Checking the created kernel image name and initrd
# ls /boot/kernel* /boot/initrd*
Now, let's perform one more step to get our system to be more like the
Installation CD -- let's emerge coldplug. While the initrd autodetects
hardware that is needed to boot your system, coldplug autodetects
everything else. To emerge and enable coldplug, type the following:
Koodilistaus 4.4: Emerging and enabling coldplug
# emerge coldplug
# rc-update add coldplug boot
7.e. Configuring Kernel Modules
Configuring the Modules
You should list the modules you want automatically loaded in
/etc/modules.autoload.d/kernel-2.4 (or 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
Koodilistaus 5.1: 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.
Koodilistaus 5.2: Editing /etc/modules.autoload.d/kernel-2.6
# nano -w /etc/modules.autoload.d/kernel-2.6
Koodilistaus 5.3: /etc/modules.autoload.d/kernel-2.6
Continue the installation with Configuring
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