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7. Configuring the Kernel
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
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
Continue now with Manual Configuration.
7.b. 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
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
# 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). We also have a Gentoo
Kernel Configuration Guide on the Gentoo wiki that might help you further.
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
<*> Reiserfs support
<*> Ext3 journalling file system support
<*> JFS filesystem support
<*> Second extended fs support
<*> XFS filesystem support
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
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
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
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
Continue the installation with Configuring your
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