How to return immediately from forked child process in Linux?

Question

I am not familar with linux C development.

my code:

....

if((pid=fork())==0){
  //child process
  //start a process, may be need to change execv to other call
  execv (workdir , args);
}else if (pid<0){
  ...
}else{
  ...
}

What I want to do is to return immediately from started new process in child process.

Because in the currrent program, execv (workdir , args); will not return. (I need to start a long running process).

What I want to do is start this long run process and return immediately in my C code, so that my C program can exit.

How can I do this? Maybe make my started new child process a daemon, how to do it by api call?

Answer 1

Something like this:

close(0); open("/dev/null", 0);
close(1);

if(open("/dev/null", O_WRONLY) < 0) {
    perror("/dev/null");
    exit(1);
}

switch(pid = fork()) {
    case -1:
        perror(argv[0]);
        exit(1);
        break;
    case 0:
        fflush(stdout);
        close(2); dup(1);
        setpgrp();
        setsid();
        execv(argv[0], argv);
        execvp(argv[0], argv);
        perror(argv[0]);
        _exit(1);
        break;
    default:
        exit(0);
        break;
}

Will fork and detach a process, and exit. It "daemonizes" the program.