/* ** daemon.c -- daemonize current process ** Copyright (c) 1999-2000 Ralf S. Engelschall, All Rights Reserved. ** ** See "Unix Programming Frequently Asked Questions": ** http://www.erlenstar.demon.co.uk/unix/faq_2.html#SEC10 */ #include "config.h" #include #include #include #include #include #ifdef HAVE_TERMIOS_H #include #endif #include "daemon.h" int daemonize(void) { int fd; int rc; /* * if we are started from init, * no need to become daemon. */ if (getppid() == 1) return 0; /* * Ignore tty related signals */ #ifdef SIGTTOU signal(SIGTTOU, SIG_IGN); #endif #ifdef SIGTTIN signal(SIGTTIN, SIG_IGN); #endif #ifdef SIGTSTP signal(SIGTSTP, SIG_IGN); #endif /* * fork so the parent can exit, this returns control to the command line * or shell invoking your program. This step is required so that the new * process is guaranteed not to be a process group leader (The next step, * setsid, would fail if you're a process group leader). */ rc = fork(); switch (rc) { case -1: return -1; case 0: break; default: _exit(0); /* exit original process */ } /* * setsid to become a process group and session group leader. Since a * controlling terminal is associated with a session, and this new session * has not yet acquired a controlling terminal our process now has no * controlling terminal, which is a Good Thing for daemons. */ #ifdef HAVE_SETSID if (setsid() == -1) return -1; #else if (setpgid(0, getpid()) == -1) return -1; #ifndef _PATH_TTY #define _PATH_TTY "/dev/tty" #endif if ((fd = open(_PATH_TTY, O_RDWR)) == -1) return -1; ioctl(fd, TIOCNOTTY, NULL); close(fd); #endif /* * fork again so the parent, (the session group leader), can exit. This * means that we, as a non-session group leader, can never regain a * controlling terminal. */ rc = fork(); switch (rc) { case -1: return -1; case 0: break; default: _exit(0); /* exit original process */ } /* * chdir("/") to ensure that our process doesn't keep any directory in * use. Failure to do this could make it so that an administrator couldn't * unmount a filesystem, because it was our current directory. * [Equivalently, we could change to any directory containing files * important to the daemon's operation.] */ chdir("/"); /* * give us complete control over the permissions of anything we write. We * don't know what umask we may have inherited. [This step is optional] */ umask(0); /* * close fds 0, 1, and 2. This releases the standard in, out, and error we * inherited from our parent process. We have no way of knowing where * these fds might have been redirected to. */ if ((fd = open("/dev/null", O_RDWR, 0)) != -1) { dup2(fd, STDIN_FILENO); dup2(fd, STDOUT_FILENO); dup2(fd, STDERR_FILENO); if (fd > 2) close(fd); } return 0; }