Question

So I have a simple fork and exec program. It works pretty good but I want to be able to detach the process that is started, I try a fork with no wait:

if((pid = fork()) < 0)
    perror("Error with Fork()");
else if(pid > 0) {
    return "";
}
else {
    if(execl("/bin/bash", "/bin/bash", "-c", cmddo, (char*) 0) < 0) perror("execl()");
    exit(0);
}

It starts the proc fine but when my main app is closed – so is my forked proc.

How do I keep the forked process running after the main proc (that started it) closes?

Thanks 😀

Answer 1

Various things to do if you want to start a detached/daemon process:

• fork again and exit the first child (so the second child process no longer has the original process as its parent pid)
• call setsid(2) to get a new session and process group
• reopen stdin/stdout/stderr to dereference the controlling tty, if there was one. Or, for example, you might have inherited a pipe stdout that will be broken and give you SIGPIPE if you try to write it.
• chdir to / to get away from the ancestor’s current directory