派生多个子进程以运行其他程序

Question

I want from parent program (called daemon) to start 5 child processes of test program with args(all 5 in parallel, not to wait to finish).

I have the following code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

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

    //missing irrelevant part where argum is set

    int status,i;
    char cmd[512];
    pid_t process_id = 0;
    for (i=0; i<=5;i++)
    {
        process_id = fork();
        if (process_id < 0)
        {
            printf("fork failed - %d!\n",i);
            continue;
        }
        else if(process_id > 0) {
            printf("process_id of child process %d \n", process_id);
        }
        else
        {
            sprintf(cmd,"./test %s",argum);
            status = system(cmd);
            exit(0);
        }
    }
    return 0;
}

it starts them but when I run ps -aux to see the processes, besides the good ones (like: ./test [args]) there are some duplicates like: sh -c ./test [args]

How can I get rid of those starting with "sh -c" ?

Answer 1

Instead of calling system() from the child, use a member of the exec*() family of functions.

Calling execXYZ() from the fork() ed off child process replaces the child process by the new process created from what had been passed to the execXYZ() call.

Please note that if execXYZ() succeeds it does not return.

---

Example for executing /bin/ls -alrt *.c :

• The execl*() members of the family expect each white-space separate command line option as a single parameter.

   execl("/bin/ls", "ls", "-alrt", "*.c", (char*) 0); execlp("ls", "ls", "-alrt", "*.c", (char*) 0); 

• The execv*() members of the family expect each white-space separate command line option in the way parameters are passed to main() :

   char * const argv[] = { "ls", "-alrt", "*.c", NULL, } execv("/bin/ls", argv); execvp("ls", argv); 

The exec*p() family members make use of the environment's variable PATH to search for the binary to be executed. So for this example (as for the system command ls ) the path does need to be specified.

---

At test program:

#include <unistd.h>  
#include <stdio.h>

/* This should list the current working directory. */

int main(void)
{
  execl("/bin/ls", "ls", "-al", "-rt", (char*) 0);
  perror("execl() failed");
  return 0;  
}

Answer 2

The simplest way to lose sight of the sh -c entries is:

sprintf(cmd, "exec ./test %s", argum);

The exec replaces the shell run by system() with the command, instead of having the shell hang around until the ./test process terminates.

The alternative is outlined by alk in his answer — use the exec*() family of functions (system calls).