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7. Configuring the Kernel

• Timezone
• Installing the Sources
• Default: Manual Configuration
• Installing Separate Kernel Modules
• Alternative: Using genkernel

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 copy it to /etc/localtime. Please avoid the /usr/share/zoneinfo/Etc/GMT* timezones as their names do not indicate the expected zones. For instance, GMT-8 is in fact GMT+8.

# ls /usr/share/zoneinfo
(Suppose you want to use GMT)
# cp /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.

We suggest using either vanilla-sources or gentoo-sources on PPC, which are both 2.6 kernels. The latter is available when you perform a networkless installation. So let's continue with emerge'ing the kernel sources. The USE="-doc" is necessary to avoid installing xorg-x11 or other dependencies at this point. USE="symlink" is not necessary for a new install, but ensures proper creation of the /usr/src/linux symlink.

# USE="-doc symlink" emerge gentoo-sources

If you take a look in /usr/src you should see a symlink named linux pointing to your current kernel source. In this case, the installed kernel source points to gentoo-sources-2.6.15. Your version may be different, so keep this in mind.

# ls -l /usr/src/linux
lrwxrwxrwx    1 root     root           22  Mar 18 16:23 /usr/src/linux -> linux-2.6.15

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 genkernel instead.

7.c. Default: 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 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). Another place to look for clues as to what components to enable is to check the kernel message logs from the successful boot that got you this far. Type dmesg to see the kernel messages.

Now, go to your kernel source directory, it's time to configure your kernel. It is recommended that you add the default settings to your configuration by first running make defconfig. After the default configuration has been generated, run make menuconfig which will fire up an ncurses-based configuration menu.

# cd /usr/src/linux
# make defconfig
# 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 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 /proc file system and Virtual memory.

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
  <*> 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:

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.

Users of NewWorld and OldWorld machines will want HFS support as well. OldWorld users require it for copying compiled kernels to the MacOS partition. NewWorld users require it for configuring the special Apple_Bootstrap partition:

File Systems --->
  [*] HFS Support

At this time, kernel preemption is still unstable on PPC and may cause compilation failures and random segfaults. It is strongly suggested that you do not use this feature.

Platform options --->
  [ ] Preemptible Kernel

If you're booting from Firewire, you'll need to enable these options. If you do not want to compile in support, you'll need to include these modules and their dependencies in an initrd.

Device Drivers --->
  IEEE 1394 (FireWire) support --->
    <*> IEEE 1394 (FireWire) support
    <*>   OHCI-1394 support
    <*>   SBP-2 support (Harddisks etc.)

If you're booting from USB, you'll need to enable these options. If you do not want to compile in support, you'll need to include these modules and their dependencies in an initrd.

Device Drivers --->
  USB support --->
    <*> Support for Host-side USB
    <*>   OHCI HCD support
    <*>   USB Mass Storage support

Do not turn off kernel framebuffer support as it is required for a successful boot. If you are using an NVIDIA based chipset, you should use the OpenFirmware framebuffer. If you are using an ATI based chipset, you should select the framebuffer driver based upon your chipset (Mach64, Rage128 or Radeon).

Device Drivers --->
  Graphics support --->
    <*> Support for frame buffer devices
    [*] Open Firmware frame buffer device support
    <*> ATI Radeon display support
    <*> ATI Rage128 display support
    <*> ATI Mach64 display support
    Console display driver support --->
      <*> Framebuffer Console 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:

# make && make modules_install

When the kernel has finished compiling, copy the kernel image to /boot (be sure that it is mounted properly on Pegasos computers). If you are using BootX to boot, we'll copy the kernel later.

Yaboot and BootX expect to use an uncompressed kernel unlike many other bootloaders. The uncompressed kernel is called vmlinux and it is placed in /usr/src/linux after the kernel has finished compiling. If you are using a Pegasos machine, the Pegasos firmware requires a compressed kernel called zImage.chrp which can be found in /usr/src/linux/arch/ppc/boot/images.

# cd /usr/src/linux
replace <kernel-version> with your kernel version
(Apple/IBM)
# cp vmlinux /boot/<kernel-version> 
(Pegasos)
# cp arch/ppc/boot/images/zImage.chrp /boot/<kernel-version> 

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:

# 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.

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

3c59x

Continue the installation with Configuring your System.

7.e. 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:

# emerge genkernel

Next, copy over the kernel configuration used by the Installation CD to the location where genkernel looks for the default kernel configuration:

# zcat /proc/config.gz > /usr/share/genkernel/ppc/kernel-config-2.6

If you are using firewire or USB to boot, you'll need to add modules to the initrd. Edit /usr/share/genkernel/ppc/modules_load and change MODULES_FIREWIRE="ieee1394 ohci1394 sbp2" for firewire support or MODULES_USB="usbcore ohci-hcd ehci-hcd usb-storage" for USB support.

Now, compile your kernel sources by running genkernel --genzimage all. For Pegasos, we will need to use a different config and create a zImage instead of the vmlinux kernel used on Apple machines. Be aware, as genkernel compiles a kernel that supports almost all hardware, this compilation can take quite a while to finish!

Note that, if your partition where the kernel should be located doesn't use ext2 or ext3 as filesystem you might need to manually configure your kernel using genkernel --menuconfig --genzimage all and add support for your filesystem in the kernel (i.e. not as a module). Users of EVMS2 or LVM2 will probably want to add --evms2 or --lvm2 as argument as well.

# genkernel --genzimage all

# genkernel --genzimage --kernel-config=/usr/share/genkernel/ppc/Pegasos 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. Be sure to also copy down the required boot arguments, these are required for a successful boot with genkernel.

# ls /boot/kernel* /boot/initramfs*

If you want your system to be more like the Installation CD you should, when your Gentoo installation is over, emerge coldplug. While the initrd autodetects hardware that is needed to boot your system, coldplug autodetects everything else. coldplug is available as one of the packages on the Package CD.

(Do this after the installation, during the GRP installation instructions)
# emerge -k coldplug
# rc-update add coldplug boot

If you want your system to react to hotplugging events, you will need to install and setup hotplug as well:

# emerge hotplug
# rc-update add hotplug default

Now continue with Configuring your System.

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