user567879 user567879 - 4 months ago 10
Linux Question

Why getppid() from the child return 1

I was running the program

#include<stdio.h>
#include <unistd.h>
main()
{
pid_t pid, ppid;
printf("Hello World1\n");
pid=fork();
if(pid==0)
{
printf("I am the child\n");
printf("The PID of child is %d\n",getpid());
printf("The PID of parent of child is %d\n",getppid());
}
else
{
printf("I am the parent\n");
printf("The PID of parent is %d\n",getpid());
printf("The PID of parent of parent is %d\n",getppid());
}
}


THe output I got was.

$ ./a.out
Hello World1
I am the parent
The PID of parent is 3071
The PID of parent of parent is 2456
I am the child
The PID of child is 3072
The PID of parent of child is 1


I couldnt understand the line


The PID of parent of child is 1


It should have been 3071?

Answer

Because parent process is finished by the time the child asks for its parent's pid.

When a process finishes, all its children are reassigned as children of the init process, which pid is 1.

Try using wait() in parent's code to wait for the child to execute. It should then work as you expect.

See this.