Linux Exposed (Unofficial guide to kernel hacking)

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Linux Exposed(Unofficial guide
to kernel hacking)
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Linux as an operating System

• What is now known as Linux began life as a small
  student project at the University of Helsinki in
  Finland. Linux Torvalds wanted a small, UNIX-like
  operating system, and so he set out to write one.
  He received help from volunteers all around the
  globe, who collaborated via bulletin-board,
  electronic mail, and the Internet to create the
  Linux operating system.

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• The crew ended up creating a rather remarkable
  operating system that works very well, is very
  stable, and rivals offerings from Microsoft,
  Apple, and Sun. Linux offers the following
  features
•   MultitaskingLinux natively runs more than one
  task (program) at a time in a UNIX-like fashion.
  It also supports preemptive multitasking, where
  priorities can be set for different processes.
•   Multi-userMany users can be networked to a
  single Linux server. Linux is the least
  expensive, and perhaps best-featured, multi-user
  operating system on the planet today.
•   User-friendlyThe X Window System interface
  and a slew of great tools make Linux easy to use.

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• Today, Linux claims half a million users, and
  that number keeps growing every day. One reason
  is costLinux itself is free of charge, and only
  those who package a Linux distribution charge for
  it (and many dont charge at all). These
  distributions, such as Red Hat Linux, vary as to
  their installation processes and accompanying
  tools.

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Linux Basics

• File Types
• Organization of files and directories
• File permissions and Linux
• An overview of X window
• Basic System Administration

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FILE TYPES

• Under Linux, a file can be one of several
  types
•   Ordinary files
•   Directories
•   Links
•   Special device files

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Organization of Files and Directories

• Directory Contents
• bin binary files
• boot boot files
• dev device drivers
• etc configuration files
• home home directory
• lib library files
• tmp temporary storage files
• usr commands
• var system definitions

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File permissions and Linux

• Because UNIX is a creature centered around
  security, Linux allows permissions to be
  designated for files and directories. If you lack
  the proper permissions, you cant change files or
  directories. The root user, of course, has the
  proper permissions to access every file in the
  Linux file system (which means that you shouldnt
  expect absolute security if youre working on a
  larger system). Under Linux, there are three
  different levels of permissions owner, group,
  and world.

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Output of ls l command-rwxrwxrwx 1 kevinr
group1 512 Apr 3 1912 test

•   The seventh column (1912) lists the time the
  file was created.
•   The sixth column (Apr 3) lists the date the
  file was created.
•   The fifth column (512) lists the size of the
  file in bytes.
•   The fourth column (group1) lists the group the
  file belongs to. (Well explain this later.)
•   The third column (kevinr) lists the owner of
  the file.
•   The second column (1) shows the number of
  links to the file.
•   The eighth column (test) lists the filename.
•   The first column (-rwxrwxrwx) lists the
  permissions associated with the file and the type
  of the file

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An overview of X window System

• X window offers a graphical interface to the Unix
  world .
• X window provides a way to deliver all the user
  interface paradigms like windows, dialog boxes
  ,buttons and menus.
• It is X window that enables the creation of the
  sophisticated graphics that make unix based
  workstations the system of choice for many
  engineering and design applications

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Window Managers And Other Clients
X-Server
Video Card
Monitor
Basic Client-Server Architecture of X-Window
Mouse/Keyboard
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Open Source Software ( OSS )

• OSS literally means software whose source is open
• To be termed as OSS ,the software should not
  restrict the user from freely using it, modifying
  it and distributing it.
• Advantages over proprietary software are -
• Longevity, Quality, portability,
  compatibility, Response time

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Hacking Linux Kernel

• Need of Kernel Compilation
• Finding Source Code
• Compiling and Linking the Kernel
• Compiling and linking modules
• Backing up the old kernel and Moving in the new
  one

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Finding Source code

• Type rpm qa grep kernel
• Choosing Kernel features
• Make xconfig
• Make menuconfig
• Make config
• Compiling and Linking Kernel
• -make dep
• -make bzImage

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Compiling and linking Modules

• make modules
• make modules_install
• Backing up old Kernel and Moving to the new
  one
• _at_/boot/grub/grub.conf file
• Image/boot/vmlinuz
• Labellinux
• Root /dev/hda5

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/boot/grub/grub.conf file (Edited)

• Image/boot/vmlinuz
• Labellinux
• Root/dev/hda5
• Image/boot/vmlinuz-2.4.2.2-2-old
• Labellinux-old
• Root/dev/hda5

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Conclusion

• If youre curious about UNIX or other
  operating systems, then Linux gives you a great
  environment to experiment with at a very
  reasonableif not freecost. If you need more
  power from your hardware than Windows or DOS
  gives you, then Linux is the operating system
  that can give it to you. If you need a robust,
  reliable server for your company Internet or
  World Wide Web services, Linux can do that just
  fine and very inexpensively. But, if you dont
  want to learn something new, dont want to
  leverage your existing hardware, and like the
  frequent crashes involved with Windows, then
  forget about Linux!

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References

• www.wikipedia.com
• www.linuxhacks.com
• www.linux.org
• www.faqs-linux.com

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Thank you
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