Thread: Programs launched from C don't stay open after launcher closes

I'd like to be able to launch a program from this C program and have that launched program stay open after this C program closes.

I've tried various solutions, and none seem to do the above. Here is some code that at least shows what's going on, and I know it doesn't work, but I wanted to at least put some effort code in here that might help.

Code:

#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <stdio.h>
#include <stdlib.h>

int main () {

    pid_t pid = -1;

    printf("\nParent is forking a child.");

    pid = fork();

    if(pid < 0){

        perror("fork");
        exit(1);

    }else if(pid == 0){

        printf("Starting child process...\n");
        printf("If I were to press ctrl-c here, both programs would close, but I want the launched program to stay open.\n");

        execlp("/usr/bin/xterm", "xterm", "-e", "top", NULL);

        // Code will never reach this point

    }else{

        printf("Parent is waiting for child id %d to complete...\n", pid);

        // Wait for procress to complete
        wait(NULL);

        printf("The child process is complete and has terminated!\nBut this program had to stay open the entire time.");
    }

    printf("Parent is now exiting...\n");

    return 0;
}

Originally Posted by Salem

Just delete the call to wait(NULL);

Works perfect now. Thank you.

SOLVED!

The child now remains open after the parents closes, but I noticed that in a loop, the child still dies if the parent is killed via ctrl-c.

How can I keep the child alive regardless of how the parent is killed?

Code:

#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>
#include <stdio.h>
#include <signal.h>

/* Compile and run with:

gcc -Wall run.c -o run -lncursesw && run 

*/

void handler(int signum) {

    write(STDOUT_FILENO, "\nExiting gracefully.", 20);
    printf("\n");
    exit(1);

}

void execute(char **arg) {

     pid_t  pid;
     int exec;

     if ((pid = fork()) < 0) {

          exit(1);

     } else if (pid == 0) {

          exec = execvp(*arg, arg);

          if (exec < 0)
               exit(1);

     } else {

        //while (waitpid(-1, NULL, WNOHANG) != pid);

     }

}

#define MAX_LINE 256 

int main(int argc, char* argv[], char*envp[]) {

   char text[MAX_LINE];
   char *args[MAX_LINE/2 + 1]; // Calculate max elements possible

   signal(SIGINT, handler);
   signal(SIGKILL, handler);
   signal(SIGTERM, handler);

   do {

      printf("\nShell: ");
      fgets(text, MAX_LINE, stdin);

      text[strlen(text) - 1] = '\0'; // strip return carriage at end of text
      args[0] = strtok(text, " ");

      for (int i = 0; args[i] != NULL; )
         args[++i] = strtok(NULL, "\"' " ); // consider quotations too

      execute(args);

   } while (strcmp(text, "exit") != 0);

   return 0;
}

Originally Posted by Salem

You could do the double fork.

Code:

if ( fork() == 0 ) {
  if ( fork() == 0 ) {
    execvp(*arg, arg);
  } else {
    _exit(0);
  }
}

daemon(3) - Linux manual page

Nice. I haven't thought of forking within a fork. I'll try it out tomorrow.

Notice that exec?() WILL return in case of error.