How can I create 7 processes using 1 parent in just 3 forks() calls? Looping is not allowed out of 7 1 is the parent one
I tried
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
int main(void) {
printf("master process is %d.\n", getpid());
fork();
fork();
fork();
wait(0);
printf("my pid is %d; my parent pid is %d\n", getpid(), getppid());
return 0;
}
and got the output
master process is 28982.
my pid is 28982; my parent pid is 31294
my pid is 28985; my parent pid is 28982
my pid is 28984; my parent pid is 28982
my pid is 28983; my parent pid is 1
my pid is 28986; my parent pid is 28984
my pid is 28988; my parent pid is 28983
my pid is 28987; my parent pid is 1
my pid is 28989; my parent pid is 28987
Total number of processes created using fork() can be found using 2^n where n is the number of times fork() is being called. Here if we calls fork() 3 times, then 2^3 processes will be created i.e 8.
Related
In order to get the PID of the child process I am doing this.
pid_t pid;
pid=fork();
if(pid==0){
//child's work
}else{
printf("The child's PID is %d",pid);
}
I want to print the child's pid from parent! So is it ok if I printf pid or do I need to use getpid()?
On success fork returns the pid of the child process, so pid will be the pid of the child process, So I'd say it's correct.
getpid is to get the pid of the current process, so it's not suited to get the child's pid.
I think this sums up the question :
#include <stdio.h>
#include <unistd.h>
int main(){
pid_t pid;
pid = fork();
if(pid == 0){
printf("In child => Own pid : %d\n", getpid());
printf("In child => Parent's pid : %d\n", getppid());
}
else{
printf("In Parent => Child's pid is %d\n", pid);
printf("In Parent => Own pid : %d\n", getpid());
}
return 0;
}
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main ( void ) {
int pid, fpid, ppid;
fpid = fork();
printf ("fpid is is %d\n", fpid);
sleep(5);
if (fpid > 0) {
pid = getpid();
ppid = getppid();
printf ("\nThis is Parent. My pid %d. My parent's pid %d\n", pid, ppid);
} else if (fpid == 0) {
sleep(1);
pid = getpid();
ppid = getppid();
printf ("\nThis is Child. My pid %d. My parent'a pid %d\n", pid, ppid);
}
}
I think when the parent process ID is 1 it means that the parent process has been terminated, so the child process gets re-parented to 1 (init, the first process). Is there any reason why the parent process would be terminated?
Parent process doesn't wait (by means of wait(2)) for the child process to complete. So, if parent exits before the child (it becomes an orphan process), then child process will be re-parented (adopted) to init process whose process ID is usually 1. Thus the child process says its parent process ID is 1.
Note that the init process' ID isn't necessarily 1 on all systems. POSIX doesn't mandate any such thing.
Because the child sleeps, by the time it calls getppid(), its parent will have likely died and the child will have been reparented to the init process (pid == 1).
I have created a program that creates two child process for a parent process. The program is to output the parent's process showing its process ID and then the two child processes showing their IDs and the ID of the parent. The parent process is supposed to capture the child process using the wait() function after the program exits and print an output.
However, my program keeps creating parent processes and giving children to those processes. I only want one parent process for the two child processes. Inside the while loop is the wait() function that is supposed to check for the changed state of the children process and print " Child 'xxx' process terminated". Instead, it is terminating some of the parent processes and other random processes.
#include<stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
int main()
{
pid_t cpid, cpid2, wpid;
int child = fork();
int child2 = fork();
int status;
if ((child = fork()) == 0){
child = cpid;
}
if((child2 = fork()) == 0){
child2 = cpid2;
}
else{
printf("I am the parent %d\n", getppid());
printf("I am the process %d created by %d\n", cpid, getppid());
printf("I am the process %d created by %d\n", cpid2, getppid());
while ((wpid = wait(&status)) > 0){
printf("Child process %d terminated\n", wpid);
}
}
return (0);
}
My output is showing me this
I am the parent 5764
I am the process 2 created by 5764
I am the process 6411548 created by 5764
I am the parent 13720
I am the process 2 created by 13720
I am the process 6411548 created by 13720
I am the parent 23612
I am the process 2 created by 23612
I am the process 6411548 created by 23612
I am the parent 15096
I am the process 2 created by 15096
I am the process 6411548 created by 15096
I am the parent 24276
I am the process 2 created by 24276
I am the process 6411548 created by 24276
I am the parent 13720
I am the process 2 created by 13720
I am the process 6411548 created by 13720
I am the parent 13720
I am the process 2 created by 13720
I am the process 6411548 created by 13720
I am the parent 5764
I am the process 2 created by 5764
I am the process 6411548 created by 5764
Child process 17016 terminated
Child process 18584 terminated
Child process 13984 terminated
Child process 8480 terminated
Child process 10816 terminated
Child process 21968 terminated
Child process 23388 terminated
Child process 11452 terminated
Child process 2776 terminated
Child process 19328 terminated
Child process 17116 terminated
Child process 18352 terminated
Child process 24276 terminated
Child process 15096 terminated
Child process 5764 terminated
Once you fork(), both the child and the parent are calling fork() again if you want to call fork() in the parent process only, check the return value before forking again.
int child = fork();
// This will be called by both, the child and the parent
int child2 = fork();
when fork() returns it returns the child PID in the parent and 0 in the child.
Start by reading the fork man page as well as the getppid / getpid man pages.
From fork's documentation:
On success, the PID of the child process is returned in the parent's
thread of execution, and a 0 is returned in the child's thread of
execution. On failure, a -1 will be returned in the parent's context,
no child process will be created, and errno will be set appropriately.
if ((child = fork()) == 0){
printf(" %u and %u", getpid(), getppid());
} else{ /* avoids error checking*/
printf("Parent - %u ", getpid());
}
The first child you fork() is forking the second child and also you're not handling else for the first fork()
#include<stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdlib.h>
int main()
{
pid_t cpid, cpid2, wpid;
int child = fork();
int child2 = fork();
int status;
if ((child = fork()) == 0){
child = cpid;
}
else {
if((child2 = fork()) == 0){
child2 = cpid2;
}
else{
printf("I am the parent %d\n", getppid());
printf("I am the process %d created by %d\n", cpid, getppid());
printf("I am the process %d created by %d\n", cpid2, getppid());
while ((wpid = wait(&status)) > 0){
printf("Child process %d terminated\n", wpid);
}
}
The way you're doing it, the first child is forking it's own child which defines a handler for the case where the returned PID != 0. So you will spawn two of the second child and handle the parent case twice.
I am trying to print the pid of the processes after running the fork() command. Here is my code-
#include <stdio.h>
#include <unistd.h>
int main(void)
{
int pid;
pid=fork();
if(pid==0)
printf("I am the child.My pid is %d .My parents pid is %d \n",getpid(),getppid());
else
printf("I am the parent.My pid is %d. My childs pid is %d \n",getpid(),pid);
return 0;
}
This is the answer I am getting-
I am the parent.My pid is 2420. My childs pid is 3601
I am the child.My pid is 3601 .My parents pid is 1910
Why is the parents id in 2nd line not 2420.Why am I getting 1910 How can I get this value?
The parent is exiting before the child performs its printf call. When the parent exits, the child gets a new parent. By default this is the init process, PID 1. But recent versions of Unix have added the ability for a process to declare itself to be the "subreaper", which inherits all orphaned children. PID 1910 is apparently the subreaper on your system. See https://unix.stackexchange.com/a/177361/61098 for more information about this.
Put a wait() call in the parent process to make it wait for the child to exit before it continues.
#include <stdio.h>
#include <unistd.h>
int main(void)
{
int pid;
pid=fork();
if(pid==0) {
printf("I am the child.My pid is %d .My parents pid is %d \n",getpid(),getppid());
} else {
printf("I am the parent.My pid is %d. My childs pid is %d \n",getpid(),pid);
wait(NULL);
}
return 0;
}
I have read this in books and also in some online forums that child process pid is assigned to its parent. But I have this code:
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
int main()
{
pid_t pid;
pid=fork();
if(pid==0)
{
printf("In Child Process\n");
printf("Child process PID : %d\n",getpid());
printf("Parent Process PID : %d\n",getppid());
}
else
{
printf("In Parent Process\n");
printf("Child PID : %d\n",getpid());
printf("Parent PID : %d\n",getppid());
}
}
It outputs:
In Parent Process
Child PID : 2061
Parent PID : 1830
In Child Process
Child process PID : 2062
Parent Process PID : 1161
But if I write a wait() function in else block, i.e:
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
int main()
{
pid_t pid;
pid=fork();
if(pid==0)
{
printf("In Child Process\n");
printf("Child process PID : %d\n",getpid());
printf("Parent Process PID : %d\n",getppid());
}
else
{
wait();
printf("In Parent Process\n");
printf("Child PID : %d\n",getpid());
printf("Parent PID : %d\n",getppid());
}
}
It outputs-
In Child Process
Child process PID : 2044
Parent Process PID : 2043
In Parent Process
Child PID : 2043
Parent PID : 1830
I'm not getting why the pid value returned by child process in first code is not the same as parent pid.
While in the second code, it is the same. Can someone please explain the reason for the above problem?
Remember that getpid returns the pid of the current process, and that getppid returns the parent pid of the current process.
So in the second example, when you call getpid in the parent process you get the pid of if itself (the parent process) and getppid gets the pid of the grand-parent.
The child pid is the value returned by fork.
More related to your problem is that you have no control over when a specific process runs in a modern multi-tasking system, which means that the child and parent processes may take turn printing out text. In your case it seems that the child process in the first example doesn't get to run until the parent process has printed its lines.
What the wait function does, is to actually wait until one child process has exited, and so the parent process will block until the child process has exited.
Joachim's answer is excellent. As additional note, you can get the child process' pid in the else branch by printing the result of fork:
#include<stdio.h>
#include<unistd.h>
#include<sys/types.h>
int main()
{
pid_t pid;
pid=fork();
if(pid==0)
{
printf("In Child Process\n");
printf("Child process PID : %d\n",getpid());
printf("Parent Process PID : %d\n",getppid());
}
else
{
wait();
printf("In Parent Process\n");
printf("Child PID : %d\n", pid); // fork returns the pid of the child
printf("Parent PID : %d\n", getpid()); // because I'm the parent
}
}
First Example:
fork returns two processes, In your first example after fork the parent starts execution and prints its pid 2061 and parent pid 1830 (of bash) and the parent will terminate without waiting for the child to finish, So when child starts executing it will print its pid 2062 and its parent has already terminated it is printing some other pid.
You please sleep() before printing parent pid when child process is running and on other terminal use command ps -l to see which pid the child is printing as a parent pid.
Second example:
You are using wait in parent process that is parent will wait untill child terminates thus child process is printing the correct parentpid because parent is still not terminated.