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1.  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.

For ${arch}-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 linux-${kernel-version}. Your version may be different, so keep this in mind.

Code Listing 1.1: Viewing the kernel source symlink

# ls -l /usr/src/linux
lrwxrwxrwx    1 root     root       12 Oct 13 11:04 /usr/src/linux -> linux-${kernel-version}

Now it is time to configure and compile your kernel source.

1.  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).

Now go to your kernel source directory and execute make menuconfig. This will fire up an ncurses-based configuration menu.

Code Listing 1.1: 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, we set up the proper cross compilation settings to make sure that the Linux kernel is built for the correct system type. To do so, set the Cross-compiler tool prefix to sparc64-unknown-linux-gnu- (including the trailing dash):

Code Listing 1.1: Identifying the proper cross compilation platform

General setup --->
  (sparc64-unknown-linux-gnu-) Cross-compiler tool prefix

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 1.1: 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

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.

Code Listing 1.1: Selecting necessary file systems

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)
  <*> Ext3 journalling file system support
  <*> Second extended fs 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:

Code Listing 1.1: 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.

Now activate the correct bus-support:

Code Listing 1.1: Activating SBUS/UPA

Console drivers --->
  Frame-buffer support --->
    [*] SBUS and UPA framebuffers             
      [*] Creator/Creator3D support     (Only for UPA slot adapter used in many Ultras)
    [*] CGsix (GX,TurboGX) support      (Only for SBUS slot adapter used in many SPARCStations)

Of course you want support for the OBP:

Code Listing 1.1: Activating OBP Support

Misc Linux/SPARC drivers --->
  [*]  /dev/openprom device support

You will also need SCSI-specific support:

Code Listing 1.1: Activating SCSI-specific support

SCSI support --->
  SCSI low-level drivers --->
    <*> Sparc ESP Scsi Driver             (Only for SPARC ESP on-board SCSI adapter)
    <*> PTI Qlogic, ISP Driver            (Only for SBUS SCSI controllers from PTI or QLogic)
    <*> SYM53C8XX Version 2 SCSI support  (Only for Ultra 60 on-board SCSI adapter)

To support your network card, select one of the following:

Code Listing 1.1: Activating networking support

Network device support --->
  Ethernet (10 or 100Mbit) --->
    <*> Sun LANCE support                   (Only for SPARCStation, older Ultra systems, and as Sbus option)
    <*> Sun Happy Meal 10/100baseT support  (Only for Ultra; also supports "qfe" quad-ethernet on PCI and Sbus)
    <*> DECchip Tulip (dc21x4x) PCI support (For some Netras, like N1)
  Ethernet (1000Mbit) --->
    <*> Broadcom Tigon3 support (Modern Netra, Sun Fire machines)

When you have a 4-port Ethernet machine (10/100 or 10/100/1000) the port order is different from the one used by Solaris. You can use sys-apps/ethtool to check the port link status.

If you're using a qla2xxx disk controller, you'll need to use a 2.6.27 kernel or newer, and you'll also need to emerge sys-block/qla-fc-firmware. Next, run make menuconfig and navigate to the Device Drivers section. You'll need to add support for loading external firmware.

Code Listing 1.1: Enabling external firmware

Device Drivers  --->
   Generic Driver Options  --->
   ()  External firmware blobs to build into the kernel binary
   ()  Firmware blobs root directory

Set "External firmware blobs" to ql2200_fw.bin and "Firmware blobs root directory" to /lib/firmware.

When you're done configuring your kernel, continue with Compiling and Installing. However, after having compiled the kernel, check its size:

Code Listing 1.1: Check kernel size

# ls -lh vmlinux
-rw-r--r--    1 root     root         2.4M Oct 25 14:38 vmlinux

If the (uncompressed) size is bigger than 7.5 MB, reconfigure your kernel until it doesn't exceed these limits. One way of accomplishing this is by having most kernel drivers compiled as modules. Ignoring this can lead to a non-booting kernel.

Also, if your kernel is just a tad too big, you can try stripping it using the strip command:

Code Listing 1.1: Stripping the kernel

# strip -R .comment -R .note vmlinux

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 1.1: Compiling the kernel

# make && make modules_install

When the kernel has finished compiling, copy the kernel image to /boot.

Code Listing 1.1: Installing the kernel

# cp arch/sparc/boot/image /boot/${kernel-name}

(Optional) Building an Initramfs

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.

Code Listing 1.1: Building an initramfs

# emerge genkernel
# genkernel --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):

Code Listing 1.1: Building an initramfs with support for LVM and software raid

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

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

Code Listing 1.1: Checking the initramfs file name

# ls /boot/initramfs*

Now continue with Kernel Modules.

1.  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 just compiled:

Code Listing 1.1: 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 1.1: Editing /etc/conf.d/modules

# nano -w /etc/conf.d/modules
modules_2_6="3c59x"

Continue the installation with (Configuring your System).

Page updated May 11, 2014

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