Linux Kernel Basics

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Linux Kernel Basics

• Walter J. Scheirer
• CSE 403

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Step 1 Obtaining the Source

• http//www.kernel.org - official source
  repository
• Versions
• 2.4.X - previous generation, standard on
  Fedora Core 1
• 2.6.X - current generation, standard on Fedora
  Core 2 and above

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Step 2 Unpack the Source

• Move the tarball to /usr/src
• mv linux.2.X.X.tar.bz2 /usr/src
• Decompress and unarchive the code
• bzip2 -cd linux.2.X.X.tar.bz2 tar xvf -
• Note this must be done as root (permissions)

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Step 3 Configuration

• Enter the source directory
• cd linux-2.X.X
• Before compilation, a .config file must be
  generated. This file contains configuration
  information specific for the machine the kernel
  is to run on.
• There are several methods to generate this file
• make config - prompts one item at a time (avoid)
• make menuconfig - text based menu system
  (recommended)
• make xconfig - X windows based configuration
  tool
• make oldconfig - merges an old configuration
  with a newer kernel

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Step 3 Configuration Cont.

• Invoke make menuconfig
• make menuconfig

Select hardware and options that appropriate for
your particular machine. Information about the
machine may be gleaned from the dmesg command.
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Step 4 Compilation

• Once you have settled on a configuration, the
  next step is to compile the kernel
• For version 2.6, simply run the make command from
  the source root
• make
• For version 2.4, you must first build the
  dependencies, then compile the compressed kernel
  image
• make dep
• make bzImage

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Step 5 Modules

• The Linux kernel is modular, thus, you must deal
  with these code snippets as well.
• For version 2.6, the modules are built
  concurrently with the kernel image. You need only
  to install them
• make modules_install
• For version 2.4, the modules must be built and
  installed
• make modules
• make modules_install
• Installed modules are located in /lib/modules/

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Step 6 Preparing for Boot

• The compressed kernel image is found within the
  source directory at arch/i386/boot/bzImage
• This image must be copied to the /boot directory
• cp arch/i386/boot/bzImage /boot/vmlinuz-2.X.X

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Step 6 Preparing for Boot Cont.

• For the kernel to appear on the next boot, the
  bootloader configuration must be altered.
• Edit /etc/grub.conf
• vi /etc/grub.conf
• Add an entry for your new kernel
• title Fedora Core (2.X.X)
• root (hd0,0)
• kernel /vmlinuz-2.X.X root/dev/hdaX rhgb
  quiet
• make sure you know the device name of /

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Problems

• If the kernel will not compile, there may be a
  conflict in your configuration - double check.
• If the kernel will not boot, several problems may
  be the culprit
• The configuration - have you selected the correct
  hardware?
• The root device - have you specified the correct
  device in the boot arguments?

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Problems - Recompiling

• If you do need to reconfigure and recompile, do
  not do the following right away
• make clean (removes compiled objects)
• make mrproper (removes compiled objects and
  the .config file)
• You will save much time by only compiling what
  needs to be added or changed.
• Compile just as you did in your first attempt
  make bzImage or make modules for 2.4, and make
  for 2.6.
• If the recompilation fails, then try a make
  clean, for a fresh source base

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Questions?