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#1 2002-07-26 11:03 PM

HectorLasso
Administrator
From: Colombia
Registered: 2002-06-12
Posts: 353

Re: 4.3 - How can I make my server a daemon?

6

There are two approaches you can take here. The first is to use inetd to do all the hard work for you. The second is to do all the hard work yourself.

If you use inetd, you simply use stdin, stdout, or stderr for your socket. (These three are all created with dup() from the real socket) You can use these as you would a socket in your code. The inetd process will even close the socket for you when you are done. For more information on setting this up, look at the man page for inetd.

If you wish to write your own server, there is a detailed explanation in "Unix Network Programming" by Richard Stevens (see 1.6 Where can I get source code for the book [book title]?). I also picked up this posting from comp.unix.programmer, by Nikhil Nair (nn201@cus.cam.ac.uk). You may want to add code to ignore SIGPIPE, because if this signal is not dealt with, it will cause your application to exit. (Thanks to ingo@milan2.snafu.de for pointing this out).


I worked all this lot out from the GNU C Library Manual (on-line
documentation).  Here's some code I wrote - you can adapt it as necessary:

/* Global variables */
...
volatile sig_atomic_t keep_going = 1; /* controls program termination */


/* Function prototypes: */
...
void termination_handler (int signum); /* clean up before termination */


int
main (void)
{
  ...

  if (chdir (HOME_DIR))         /* change to directory containing data 
                                    files */
   {
     fprintf (stderr, "`%s': ", HOME_DIR);
     perror (NULL);
     exit (1);
   }

   /* Become a daemon: */
   switch (fork ())
     {
     case -1:                    /* can't fork */
       perror ("fork()");
       exit (3);
     case 0:                     /* child, process becomes a daemon: */
       close (STDIN_FILENO);
       close (STDOUT_FILENO);
       close (STDERR_FILENO);
       if (setsid () == -1)      /* request a new session (job control) */
         {
           exit (4);
         }
       break;
     default:                    /* parent returns to calling process: */
       return 0;
     }

   /* Establish signal handler to clean up before termination: */
   if (signal (SIGTERM, termination_handler) == SIG_IGN)
     signal (SIGTERM, SIG_IGN);
   signal (SIGINT, SIG_IGN);
   signal (SIGHUP, SIG_IGN);

   /* Main program loop */
   while (keep_going)
     {
       ...
     }
   return 0;
}

void
termination_handler (int signum)
{
  keep_going = 0;
  signal (signum, termination_handler);
}

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