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Handbook:IA64/Installation/Kernel

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IA64 Handbook
Installation
About the installation
Choosing the media
Configuring the network
Preparing the disks
Installing stage3
Installing base system
Configuring the kernel
Configuring the system
Installing tools
Configuring the bootloader
Finalizing
Working with Gentoo
Portage introduction
USE flags
Portage features
Initscript system
Environment variables
Working with Portage
Files and directories
Variables
Mixing software branches
Additional tools
Custom package repository
Advanced features
Network configuration
Getting started
Advanced configuration
Modular networking
Wireless
Adding functionality
Dynamic management


Installing the sources

The core around which all distributions are built is the Linux kernel. It is the layer between the user programs and the system hardware. Gentoo provides its users several possible kernel sources. A full listing with description is available at the Kernel overview page.

For ia64-based systems Gentoo recommends the sys-kernel/gentoo-sources package.

Choose an appropriate kernel source and install it using emerge:

root #emerge --ask sys-kernel/gentoo-sources

This will install the Linux kernel sources in /usr/src/ in which a symbolic link called linux will be pointing to the installed kernel source:

root #ls -l /usr/src/linux
lrwxrwxrwx    1 root   root    12 Oct 13 11:04 /usr/src/linux -> linux-3.16.5-gentoo

Now it is time to configure and compile the kernel sources. There are two approaches for this:

  1. The kernel is manually configured and built.
  2. A tool called genkernel is used to automatically build and install the Linux kernel.

We explain the manual configuration as the default choice here as it is the best way to optimize an environment.

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 no-one even remembers that it was difficult ;)

However, one thing is true: it is vital to know the system when a kernel is configured manually. Most information can be gathered by emerging sys-apps/pciutils which contains the lspci command:

root #emerge --ask sys-apps/pciutils
Note
Inside the chroot, it is safe to ignore any pcilib warnings (like pcilib: cannot open /sys/bus/pci/devices) that lspci might throw out.

Another source of system information is to run lsmod to see what kernel modules the installation CD uses as it might provide a nice hint on what to enable.

Now go to the kernel source directory and execute make menuconfig. This will fire up menu-driven configuration screen.

root #cd /usr/src/linux
root #make menuconfig

The Linux kernel configuration has many, many sections. Let's first list some options that must be activated (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 out further.

Activating required options

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

Next select the exact processor type. It is also recommended to enable MCE features (if available) so that users are able to be notified of any hardware problems. On some architectures (such as x86_64), these errors are not printed to dmesg, but to /dev/mcelog. This requires the app-admin/mcelog package.

Also select Maintain a devtmpfs file system to mount at /dev so that critical device files are already available early in the boot process (CONFIG_DEVTMPFS and CONFIG_DEVTMPFS_MOUNT):

KERNEL 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

Verify SCSI disk support has been activated (CONFIG_BLK_DEV_SD):

KERNEL Enabling SCSI disk support
Device Drivers --->
   SCSI device support  --->
      <*> SCSI disk support

Now go to File Systems and select support for the filesystems you use. Don't compile the file system that is used for the root filesystem as module, otherwise the Gentoo system will not be able to mount the partition. Also select Virtual memory and /proc file system. Select one or more of the following options as needed by the system (CONFIG_EXT2_FS, CONFIG_EXT3_FS, CONFIG_EXT4_FS, CONFIG_MSDOS_FS, CONFIG_VFAT_FS, CONFIG_PROC_FS, and CONFIG_TMPFS):

KERNEL Selecting necessary file systems
File systems --->
  <*> Second extended fs support
  <*> The Extended 3 (ext3) filesystem
  <*> The Extended 4 (ext4) filesystem
  <*> Reiserfs support
  <*> JFS filesystem support
  <*> XFS filesystem support
  <*> Btrfs filesystem support
  DOS/FAT/NT Filesystems  --->
    <*> MSDOS fs support
    <*> VFAT (Windows-95) fs support
 
Pseudo Filesystems --->
    [*] /proc file system support
    [*] Tmpfs virtual memory file system support (former shm fs)

If PPPoE is used to connect to the Internet, or a dial-up modem, then enable the following options (CONFIG_PPP, CONFIG_PPP_ASYNC, and CONFIG_PPP_SYNC_TTY):

KERNEL Selecting PPPoE necessary drivers
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.

Don't forget to include support in the kernel for the network (Ethernet or wireless) cards.

Most systems also have multiple cores at their disposal, so it is important to activate Symmetric multi-processing support (CONFIG_SMP):

KERNEL Activating SMP support
Processor type and features  --->
  [*] Symmetric multi-processing support
Note
In multi-core systems, each core counts as one processor.

If USB input devices (like keyboard or mouse) or other USB devices will be used, do not forget to enable those as well (CONFIG_HID_GENERIC and CONFIG_USB_HID, CONFIG_USB_SUPPORT, CONFIG_USB_XHCI_HCD, CONFIG_USB_EHCI_HCD, CONFIG_USB_OHCI_HCD):

KERNEL Activating USB support for input devices
Device Drivers --->
  HID support  --->
    -*- HID bus support
    <*>   Generic HID driver
    [*]   Battery level reporting for HID devices
      USB HID support  --->
        <*> USB HID transport layer
  [*] USB support  --->
    <*>     xHCI HCD (USB 3.0) support
    <*>     EHCI HCD (USB 2.0) support
    <*>     OHCI HCD (USB 1.1) support


Architecture specific kernel configuration

Select the correct system type and processor type. DIG-compliant is a good default choice. When installing on an SGI system make sure to select the SGI system type, the kernel may just lock up and refuse to boot otherwise.

KERNEL Proper IA64 processor selection
System type --->
  (Change according to the system)
  DIG-compliant
Processor type --->
  (Change according to the system)
  Itanium 2

Compiling and installing

With the kernel configured, it is time to compile and install it. Exit the configuration and start the compilation process:

root #make && make modules_install
Note
It is possible to enable parallel builds using make -jX with X being the number of parallel tasks that the build process is allowed to launch. This is similar to the instructions about /etc/portage/make.conf earlier, with the MAKEOPTS variable.

When the kernel has finished compiling, copy the kernel image to /. Use whatever name is appropriate for your kernel choice and remember it as it will be referred to later on when configuring the bootloader. Remember to replace vmlinuz with the name and version of the installed kernel.

root #cp vmlinux.gz /boot/vmlinuz



Optional: Building an initramfs

In certain cases it is necessary to build an initramfs - an initial ram-based file system. The most common reason is when important file system locations (like /usr/ or /var/) are on separate partitions. With an initramfs, these partitions can be mounted using the tools available inside the initramfs.

Without an initramfs, there is a huge 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 sys-kernel/genkernel first, then have it generate an initramfs:

root #emerge --ask sys-kernel/genkernel
root #genkernel --install initramfs

In order to enable specific support in the initramfs, such as LVM or RAID, add in the appropriate options to genkernel. See genkernel --help for more information. In the next example support is enabled for LVM and software RAID (mdadm):

root #genkernel --lvm --mdadm --install initramfs

The initramfs will be stored in /boot/. The resulting file can be found by simply listing the files starting with initramfs:

root #ls /boot/initramfs*

Now continue with Kernel modules.

Alternative: Using genkernel

If a manual configuration looks too daunting, then using genkernel is recommended. It will configure and build the kernel automatically.

genkernel works by configuring a kernel nearly identically to the way the installation CD kernel is configured. This means that when genkernel is used to build the kernel, the system will generally detect all hardware at boot-time, just like the 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 sys-kernel/genkernel ebuild:

root #emerge --ask sys-kernel/genkernel

Next, edit the /etc/fstab file so that the line containing /boot/ as second field has the first field pointing to the right device. If the partitioning example from the handbook is followed, then this device is most likely with the ext2 file system. This would make the entry in the file look like so:

root #nano -w /etc/fstab
FILE /etc/fstabConfiguring the /boot mountpoint
/boot	ext2	defaults	0 2
Note
Further in the Gentoo installation, /etc/fstab will be configured again. The /boot setting is needed right now as the genkernel application reads in this configuration.

Now, compile the 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
If the boot partition doesn't use ext2 or ext3 as filesystem it might be necessary to manually configure the kernel using genkernel --menuconfig all and add support for this particular filesystem in the kernel (i.e. not as a module). Users of LVM2 will probably want to add --lvm as an argument as well.
root #genkernel all

Once genkernel completes, a kernel, full set of modules and initial ram disk (initramfs) 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 this information is used when the boot loader configuration file is edited. The initrd will be started immediately after booting to perform hardware autodetection (just like on the installation CD) before the "real" system starts up.

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

Kernel modules

Configuring the modules

Note
Hardware modules are optional to be listed manually. udev will normally load all hardware modules that are detected to be connected in most cases. However, it is not harmful for automatically detected modules to be listed. Sometimes exotic hardware requires help to load their drivers.

List the modules that need to be loaded automatically in /etc/modules-load.d/*.conf files one module per line. Extra options for the modules, if necessary, should be set in /etc/modprobe.d/*.conf files.

To view all available modules, run the following find command. Don't forget to substitute "<kernel version>" with the version of the kernel just compiled:

root #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/modules-load.d/network.conf file and enter the module name in it. The actual file name is insignificant to the loader.

root #mkdir -p /etc/modules-load.d
root #nano -w /etc/modules-load.d/network.conf
FILE /etc/modules-load.d/network.confForce loading 3c59x module
3c59x

Continue the installation with Configuring the system.

Optional: Installing firmware

Some drivers require additional firmware to be installed on the system before they work. This is often the case for network interfaces, especially wireless network interfaces. Also, modern video chips, from vendors like AMD, NVidia, and Intel when using open source drivers, often need external firmware files. Most of the firmware is packaged in sys-kernel/linux-firmware:

root #emerge --ask sys-kernel/linux-firmware


← Installing base system Home Configuring the system →


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