Skip to main content

Process ID and Parent Process ID in Linux

When referring to process IDs in a C or C++ program, always use the pid_t typedef, which is defined in <sys/types.h>.A program can obtain the process ID of the process it’s running in with the getpid() system call, and it can obtain the process ID of its parent process with the getppid() system call. For instance, the program in Listing 3.1 prints its process ID and its parent’s process ID.

   1:  // Printing the process ID and parent process ID
   2:  #include <stdio.h>
   3:  #include <unistd.h>
   4:  int main ()
   5:  {
   6:  printf (“The process ID is %d\n”, (int) getpid ());
   7:  printf (“The parent process ID is %d\n”, (int) getppid ());
   8:  return 0;
   9:  }
 
fork

When a program calls fork, a duplicate process, called the child process, is created. The parent process continues executing the program from the point that fork was called. The child process, too, executes the same program from the same place. So how do the two processes differ? First, the child process is a new process and therefore has a new process ID, distinct from its parent’s process ID.One way for a program to distinguish whether it’s in the parent process or the child process is to call getpid. However, the fork function provides different return values to the parent and child processes—one process “goes in” to the fork call, and two processes “come out,” with different return values.The return value in the parent process is the process ID of the child.The return value in the child process is zero. Because no process ever has a process ID of zero, this makes it easy for the program whether it is now running as the parent or the child process.

The following example show the fork to duplicate a program’s process. Note that the first block of the if statement is executed only in the parent process, while the else clause is executed in the child process.


   1:  // to create a process using fork()
   2:  #include <stdio.h>
   3:  #include <sys/types.h>
   4:  #include <unistd.h>
   5:  int main ()
   6:  {
   7:  pid_t child_pid;
   8:  printf (“the main program process ID is %d\n”, (int) getpid ());
   9:  child_pid = fork ();
  10:  if (child_pid != 0) {
  11:  printf (“this is the parent process, with id %d\n”, (int) getpid ());
  12:  printf (“the child’s process ID is %d\n”, (int) child_pid);
  13:  }
  14:  else
  15:  printf (“this is the child process, with id %d\n”, (int) getpid ());
  16:  return 0;
  17:  }

Observation:

The program can be compiled using gcc compiler

$: gcc –o <linkname> <filename.c>

$: ./linkname

Comments

Popular posts from this blog

Ant Colony algorithm using NS2

Ant Colony Algorithm in NS2 for Wired Networks. Please follow the video for full instructions  I am running in Ubuntu 20.04 There are multiple files in Ant Colony (we use a protocol called Antnet) which i have already included in my blog called https://www.nsnam.com  Lets go to my Blog. And Search for Ant Colony and Download the complete folder AntNet as shown in the video. Now Copy paste the files in their corresponding location: My Location if ns2 is  /home/pradeepkumar/ns-allinone-2.35/ns-2.35/ Inside this folder, the files have to be pasted in differnet sub folders...  Let me show you one by one... cmu-trace.cc and cmu-trace.h have to be pasted to ~trace/ drop-tail.cc and drop-tail.h ---- ~queue/ Makefile.in to be replaced in the ns-2.35/ folder. ns-default.tcl, ns-lib.tcl and ns-packet.tcl to be pasted at  ~tcl/lib packet.h to be replaced at common/ folder. priqueue.cc and priqueue.h to be pasted at queue/ antnet / folder have to be copied to ns-2.35/ folder (this is very imp

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 nsnam.org 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/ $] ./build.py --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

ns3 installation in Ubuntu 16.04

This post serves the installation instructions of ns3 in ubuntu 16.04 version. Some of my students are working in ns3, this post will benefit them in installing ns3. OS Used: Ubuntu 16.04.4 ns3 version: ns3 version 3.27 The same procedure will be applied for OS like Debian, Linux Mint. Fresh installation of Ubuntu 16.04 Let you try the fresh installation of ubuntu in your hard disk along with windows. Installation of ns3 dependencies ns3 needs so many dependencies, developmental libraries, drivers, etc. so install all those $] sudo apt update  $] sudo apt upgrade $] sudo apt-get install build-essential autoconf automake libxmu-dev python-pygoocanvas python-pygraphviz cvs mercurial bzr git cmake p7zip-full python-matplotlib python-tk python-dev python-kiwi python-gnome2 python-gnome2-desktop-dev python-rsvg qt4-dev-tools qt4-qmake qt4-qmake qt4-default gnuplot-x11 wireshark The above command make take some time to download, compile and install it, Be Patie