Skip to main content

Main Algorithms of a Linux Kernel


  • Signals are one of the oldest facilities of Inter Process Communication.
  • Signals are used to inform the processes about the events.
  • signals will be sent via the following function (by the Kernel)

int send_sig_info(int sig, struct siginfo *info, struct task_struct *);

sig – refers the signal number

info – refers the sender

t – refers to the tasks (the kernel may send signals to many processes)

Booting the System

There are many bootloaders available for linux, the common ones being the LILO and the GRUB loader

LILO – LInux LOader

GRUB – GRand unified Bootloader

The steps while booting the kernel (only relevant steps are given)

  • Entry point at start which is available at arch/x86/boot/setup.S (This is responsible for initializing the hardware (assembler code)
  • Once the hardware is initialized, the process is switched to protected mode by setting a bit word in the machine status word.
  • Next the assembler instruction,       jmpi 0×100000 _KERNEL_CS, jumps to the start address of the 32 bit code of the actual operating system kernel and continues from startup_32 and in the file arch/x86/kernel/head.S . More sections of the hardwares are initialized here like Memory Management unit (Page tables), the Co processor, and the environment (stack, environment,etc)
  • The first C function start_kernel() from init/main.c is called
  • the following list the assembly linkage of the start_kernel function

asmlinkage void __init start_kernel(void)


char * command_line;

printk(linux_banner); //print kernel, the banner

setup_arch(&command_line);//architecture dependent codes relevant to x86


init_IRQ(); //hardware interrupt initialization

sched_init(); //initialize the schedules


softirq_init(); //soft interrupts

console_init();//initialize the console

init_modules();//initialize the modules (device drivers)


  • the init is called (will be searched in /sbin/init or /etc/init or /bin/init). if the init is not available, then a shell (/bin/bash) will be opened for debugging

Hardware  interrupts (IRQ)

Interrupts are used to allow the hardware to communicate with the operating system, there are two problems while writing interrupt routine,

  • firstly, The interrupt routines should serve the hardware as quickly as possible
  • secondly, large amount is to be handled by the interrupt routine

This can be solved by the following mechanisms

  • disabling all the software interrupts while servicing the hardware interrupts.
  • the processing of data is carried out asynchronously by the software interrupts through “tasklets ” or “bottom halves”

Software Interrupts

  • It is like a hardware interrupt but can be started only at certain times
  • The number of interrupts is limited
  • enum {HI_SOFTIRQ, NET_TX_SOFTIRQ, NET_RX_SOFTIRQ,TASKLET_SOFTIRQ}; the date types tells the software interrupts for hi priority software interrupts, Network Tranmssion and Receiving Interrupt and tasklet interrupt). upon interrupt is generated, the Interrupt routine will be executed


Popular posts from this blog

Installing ns-3.34 in Ubuntu 20.04

This post shows how to install ns 3.34 in Ubuntu 20.04 LTS Prerequisites: Fresh installation of Ubuntu Version 20.04 LTS  ns3.34 can be downloaded from here Follow the video link for complete step by step instructions on the installation.  This version fixes the compilation issues of (bug in ns3.33)  Issue the following commands after opening a terminal  $ sudo apt update $ sudo apt install g++ python3 python3-dev python-dev pkg-config sqlite3 python3-setuptools git qt5-default gir1.2-goocanvas-2.0 python3-gi python3-gi-cairo python3-pygraphviz gir1.2-gtk-3.0 ipython3 openmpi-bin openmpi-common openmpi-doc libopenmpi-dev autoconf cvs bzr unrar openmpi-bin openmpi-common openmpi-doc libopenmpi-dev tcpdump wireshark libxml2 libxml2-dev Unzip or untar the ns-allinone-3.34.tar.bz2 in the home folder (in my case its /home/pradeepkumar) $ cd ns-allinone-3.34/ $ ./ --enable-examples --enable-tests  Once the installation is completed, you may get an output show

Installation of ns3 in Windows 10 and Windows 11 OS using WSL (Windows Subsystem for Linux)

This post shows how to install ns-3.33 in Windows 10 through WSL (Windows Subsystem for Linux) This posts works for Windows 11 also (I have tested it on a Windows 11 ISO and it works the Same way as mentioned in the following post.) This post will work for ns-3.3x version. Prerequisites : Install Windows Subsystem for Linux with GUI: Please refer the following video  System Information: OS used: Windows 10 and WSL (Ubuntu 20.04) GUI: XServer for Windows NS3 Version: ns-3.33 See the following complete video on how to install ns3 in Windows 10 Step 0 : Open XLaunch Step 1 :  Open WSL using PowerShell and open it as Administrator Command:/  wsl $ xfce4-session The GUI of Ubuntu Opens within Windows 10 OS. Step 2 : Download ns3 from website through Mozilla Firefox browser Step 3: Open a Terminal  $ sudo apt update $ sudo apt install build-essential autoconf automake libxmu-dev python3-pygraphviz cvs mercurial bzr git cmake p7zip-full python3-matplotlib python-tk python3-dev qt5-q

Installing NS-3.32 in Ubuntu 20.04

This is about installing ns version 3.32 in Ubuntu 20.04 LTS. #ns3 #ns3 .32 #networksimulation The commands used in the video are given here. $] sudo apt update $] sudo apt install build-essential autoconf automake libxmu-dev python3-pygraphviz cvs mercurial bzr git cmake p7zip-full python3-matplotlib python-tk python3-dev qt5-qmake qt5-default gnuplot-x11 wireshark Download the ns-allinone-3.32.tar.bz2 package from and copy it to /home/ folder See the full video for detailed instructions Extract it either in GUI or using command $] tar jxvf ns-allinone-3.32.tar.bz2 $] cd ns-allinone-3.32/ $] ./ --enable-examples --enable-tests The above command will take some time to install all the packages  You can see the output as shown below ns3 To check whether ns3 installed successfully, use the following commands. $] cd ns-3.32/ $] ./waf --run hello-simulator You should get the output as Hello Simulator $] ./waf --run first This is the example from the ns-3.32/exa