Nope, not quite.
I was able to make a father process with more then one child by myself. But what I really want is after creating a number of child prcesses, starting with one of them as a father, it should again fork a few times, thus obtaing a tree-structure of processes.
So I guess I need some kind of recursive algorithm to do that. But here comes the problem: if I fork in a recursive way, I can't seem to get that tree structure right.
And also another problem: using the program shown by Perderabo and also my own, I changed the line:
printf("I am a child process and my pid is %d\n", getpid());
with this one:
printf("I am a child process id=%d father=%d\n",getpid(),getppid());
so I could see if the father is the right one, and after a few forks, all the child processes were generated by the process with pid=1. I avoided that by placing a sleep(2) command right before the end of the program, but I'm wondering: who's this process and is there another way to stop that?
Your post helped me out with a fork I am writing, but I am having a little trouble because the execve command only executes the "ls" command when i type one in - no matter WHAT command I type in. if i modify execve("/bin/ls", .....) to only read execve("/bin/", .....), it doesnt execute ANYTHING. what do i need to do? Here is my code:
Code:
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <iostream.h>
#include <string>
#include <iomanip.h>
#include <sys/wait.h>
main()
{
cout<<"You have entered my 1814 shell"<<endl;
// string command;
char line[1024], *doit[20];
int n, pid, parentpid, childpids[0];
while (line !="exit")
{
cout<<"GIMME:#";
cin.getline(line,sizeof(line));
cout<<"The command you typed was: " <<line<<endl;
if (strcmp(line,"exit")==0)
return 0;
parentpid=getpid();
printf("I am the parent process and my pid is %d\n", getpid());
if (pid=fork())
{
int status;
waitpid(-1, &status, 0);
childpids[n]=pid;
}
else
{
printf("I am a child process and my pid is %d\n", getpid());
doit[0] = "ls";
doit[1] = "-la";
doit[2] = NULL;
execve("/bin/ls", doit, NULL);
exit(0);
}
printf("I am still the parent process and my pid is %d\n",
getpid());
}//end of while
if (line =="exit")
return 0;
printf("I am still the parent process and my pid is %d\n", getpid());
}//end of main
is not going to run a "date" command. It's simply incredible that you think it might. execve is not going to ignore its arguments. You need to parse the command line and dynamically build arguments for the execve call.
And you should switch to execv anyway. As it is, you are clobbering the environment.
And, for now, require the user to enter "/usr/bin/date" rather than "date" so you don't need to search the PATH. You can get fancy later.
i meant to have commented that code out. I was using it for another purpose. At any rate, I got my shell to work. thaaaaaaaaaanx
Code:
mars:$ cat modshell1.3.cpp
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <iostream.h>
#include <string>
#include <iomanip.h>
#include <sys/wait.h>
int main()
{
cout<<"You have entered my 1814 shell"<<endl;
// string command;
char line[256], *doit[20];
int n, pid, parentpid, childpids[0];
while (line !="exit")
{
cout<<"GIMME:#";
cin.getline(line, 256);
// cin.getline(line,sizeof(line));
cout<<"The command you typed was: " <<line<<endl;
doit[0] = strtok(line, " ");
int i=1;
while (doit[i]=strtok(NULL, " "))
i++;
doit[i]=NULL;
if (strcmp(line,"exit")==0)
return 0;
parentpid=getpid();
printf("I am the parent process and my pid is %d\n", getpid());
if (pid=fork())
{
int status;
waitpid(-1, &status, 0);
childpids[n]=pid;
}
else
{
printf("I am a child process and my pid is %d\n", getpid());
cout<<"Parameters are: "<<endl;
for (int j=0; j<i; j++)
cout<<doit[j]<<endl;
cout<<" EXECUTE CHILD"<<endl;
execve(doit[0], doit, NULL);
exit(0);
}
cout<<" KILL CHILD AND RETURN TO PARENT"<<endl;
printf("I am still the parent process and my pid is %d\n",
getpid());
}//end of while
if (line =="exit")
return 0;
printf("I am still the parent process and my pid is %d\n", getpid());
}//end of main
Compiling with g++ on an OpenBSD 3.0 box, I get a "Memory Fault", and it dumps core when I try to run a command, like "ls".
The exit value is 139, and gdb reports a "Program received signal SIGSEGV, Segmentation fault.
0x1ad8 in main () "
Is this machine specific?
(I'm a no-C / C++ goof - Trying, though)
I just downloaded the code and works for me on Sun. I don't see anything machine specific here. He is not testing for too many arguments and, if you entered 20 or more arguments to that ls, you could get a memory fault. Could that be it?
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