Chapter 9 Extra 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