POSIX_SPAWN_SETSID

If the POSIX_SPAWN_SETPGROUP flag is not set ...

If neither the POSIX_SPAWN_SETPGROUP flag nor the POSIX_SPAWN_SETSID flag is set ...

If the POSIX_SPAWN_SETSID flag is set in the spawn-flags attribute of the object referenced by attrp, the child process shall be the session leader of a new session, shall be the process group leader of a new process group, and shall have no controlling terminal. The process group ID of the child process shall be set equal to the process ID of the child process. The child process shall be the only process in the new process group and the only process in the new session.

If both the POSIX_SPAWN_SETPGROUP flag and the POSIX_SPAWN_SETSID flag are set in the spawn-flags attribute of the object referenced by attrp, the behavior is unspecified.

If POSIX_SPAWN_SETSID is set in the spawn-flags attribute of the object referenced by attrp, and posix_spawn() or posix_spawnp() fails while creating the new session, changing the child's session ID, or changing the child’s process group, an error value shall be returned as described by setsid() (or, if the error occurs after the calling process successfully returns, the child process shall exit with exit status 127).

    #define POSIX_SPAWN_RESETIDS 0x20

    #define POSIX_SPAWN_SETSID   0x40   

    /* Worry about process group */

    /* Worry about creating a new session */
    if (attrp->posix_attr_flags & POSIX_SPAWN_SETSID)
    {
        /* Create a new session */
        if (setsid() == -1)
        {
            /* Failed */
            _exit(127);
        }
    }

    /* Worry about process group */

    exit(127);

    _exit(127);