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 systems, we will use gentoo-sources (contains additional patches for extra features).

Now install it using emerge.

# 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-. Your version may be different, so keep this in mind.

# ls -l /usr/src/linux
lrwxrwxrwx    1 root   root    12 Oct 13 11:04 /usr/src/linux -> 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 genkernel instead.

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.

# 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).

Make sure that every driver that is vital to the booting of your system (such as SCSI controller, ...) is compiled in the kernel and not as a module, otherwise your system will not be able to boot completely.

Now select the correct system type and processor type. If you don't know what kind of IA64 system type you have, DIG-compliant is a good default choice. If you are installing on an SGI system make sure you select the SGI system type, your kernel may just lock up and refuse to boot otherwise.

System type --->
  (Change according to your system)
  DIG-compliant
Processor type --->
  (Change according to your system)
  Itanium 2

Next select Maintain a devtmpfs file system to mount at /dev so that critical device files are already available early in the boot process.

Device Drivers --->
  Generic Driver Options --->
    [*] Maintain a devtmpfs filesystem to mount at /dev
    [ ]   Automount devtmpfs at /dev, after the kernel mounted the rootfs

Now 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 and /proc file system.

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

(Be sure to enable VFAT support for the EFI partition)
  DOS/FAT/NT Filesystems  --->
    <*> VFAT (Windows-95) fs support

(Enable GPT partition label support if you used that previously
-*- Enable the block layer --->
    ...
    Partition Types --->
    [*] Advanced partition selection
      ...
      [*] EFI GUID Partition 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 --->
  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 ethernet card.

If you have an Intel CPU that supports HyperThreading (tm), or you have a multi-CPU system, you should activate "Symmetric multi-processing 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:

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

When you've finished configuring the kernel, continue with 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:

# make && make modules_install

When the kernel has finished compiling, copy the kernel image to /. 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 vmlinuz with the name and version of your kernel.

# cp vmlinux.gz /boot/vmlinuz

If you use a specific partition layout where important file system locations (like /usr or /var) are on separate partitions, then you will need to setup an initramfs so that this partition can be mounted before it is needed.

Without an initramfs, you risk that the system will not boot up properly as the tools that are responsible for mounting the file systems need information that resides on those file systems. An initramfs will pull in the necessary files into an archive which is used right after the kernel boots, but before the control is handed over to the init tool. Scripts on the initramfs will then make sure that the partitions are properly mounted before the system continues booting.

To install an initramfs, install genkernel first, then have it generate an initramfs for you.

# emerge genkernel
# genkernel --bootdir=/. --no-mountboot --install initramfs

If you need specific support in the initramfs, such as lvm or raid, add in the appropriate options to genkernel. See genkernel --help for more information, or the next example which enables support for LVM and software raid (mdadm):

# genkernel --bootdir=/. --no-mountboot --lvm --mdadm --install initramfs

The initramfs will be stored in /. You can find the file by simply listing the files starting with initramfs:

# ls /initramfs*

Now continue with Kernel Modules.