Chapter 9Extra Topics

The Kernel

• Core of the operating system

• Similar to UNIX kernel

• Originally developed and still controlled by Linus Torvalds

• uname -r

• Current latest version: 2.6.x

• Version names follow the convention:• major.minor.patchlevel

• minor• even : stable

• odd : development

What’s a Kernel

• Can be seen as an executive, system monitor

• Controls and provides access to the hardware

• Implements and supports • processes, files, devices, etc.

• Schedules system resources• Memory, Processor time, disk space, peripherals

• Enforce security, protection

• Respond to user commands

Kernel Design Goals

• Performance• Utilize resources with low overhead

• Extensibility

• Capability• features, compatibility

• Security

• Portability

• Stability

Kernel Overview

Building the Kernel

• For• keeping up with new kernel releases

• Remove device drivers not needed: better performance

• Obtain sources

• From Internet• from ftp://ftp.kernel.org

• main release usually a tar-zipped file

• patches released as seperate files

• maybe installed already: /usr/src/linux

• apt-get

Patching

• Patches are available to the last release• fix bugs, holes

• provide new features

• Can be applied using the patch command• download the patch file to /usr/src/linux

• extract

• patch -pl < patch-2.2.x

Building the Kernel: Steps

• Look in Documentation/Changes for the list of requirements

• README for detailed information for building

• run make config or make xconfig• make oldconfig if already built the kernel earlier

• run make dep to build dependencies• run make clean to clean up

• build the kernel: make bzimage

• copy the bzimage and System.map to /boot

diff - comparing files

• Utility to compare files

• Gives instructions on how to make them similar

• a: add

• c: change

• d: delete

• diff file1 file2• changes in file1 to make it like file2

• l1al2, l3: append lines l2 to l3 from file2 after line1 in file1

• l1,l2cl3,l4 : change lines l1 to l2 in file1 to l3 to l4 in file2

• l1,l2dl3 : delete lines l1 to l2 in file1

uniq: Deleting repeated lines

• Deleting repeated lines in a file

• uniq sample• output the lines in sample without repitition

• uniq sample out• output the non-repeated lines in sample to out

• uniq -c sample• give counts of repetitions

• uniq -d sample• give the lines that are repeated in sample

• uniq -d sample out• save the repeated lines in sample to out

find: advanced file searching

• searches for files with specified criteria in specified directories

• find ~ -name *.doc -print• search for all .doc files in my home directory

• -print option to print the results

• enclose complex search criteria in \( \)

• -o for OR

• find ~ \( -name *.doc -o -name *.ppt \) -print• search for all .doc and .ppt files in my home directory

whereis and which

• whereis: locate the directories where a command is• useful when shell cannot find the command

• command may not be in PATH

• which: similar to whereis• prints location of the command

• helpful when more than two commands with same name exist