Re: start emacs without creating frames and connect with emacsclient later

[Dan Nicolaescu <dann@ics.uci.edu>]

"Richard M. Stallman" <rms@gnu.org> writes:

  >     Should something like this go in?  We do have a feature freeze, but this
  >     is quite simple, and it completes the multi-tty functionality, which is
  >     one of the major features of 23.1.
  > 
  > I think it should go in
  > provided you write the text for etc/NEWS AND all the relevant manuals.

I got a lot of private emails from people very happy to use this
feature.  
And some people actually want to distribute the patch.  So here's an
updated version including documentation.

Index: doc/emacs/cmdargs.texi
===================================================================
RCS file: /cvsroot/emacs/emacs/doc/emacs/cmdargs.texi,v
retrieving revision 1.3
diff -u -3 -p -r1.3 cmdargs.texi
--- doc/emacs/cmdargs.texi	22 Jan 2008 23:53:34 -0000	1.3
+++ doc/emacs/cmdargs.texi	1 Sep 2008 13:56:17 -0000
@@ -277,6 +277,15 @@ option and @samp{-Q} are the only option
 Start emacs with minimum customizations.  This is like using @samp{-q}
 and @samp{--no-site-file}, but also disables the startup screen.
 
+@item -daemon
+@opindex -daemon
+@itemx --daemon
+@opindex --daemon
+Start emacs in background as a daemon (i.e. it will disconnect from the
+terminal), do not open any frames and start the server.  Clients can
+connect and create graphical or terminal frames using
+@code{emacsclient}.
+
 @item --no-splash
 @opindex --no-splash
 @vindex inhibit-splash-screen
Index: etc/NEWS
===================================================================
RCS file: /cvsroot/emacs/emacs/etc/NEWS,v
retrieving revision 1.1843
diff -u -3 -p -r1.1843 NEWS
--- etc/NEWS	31 Aug 2008 02:13:38 -0000	1.1843
+++ etc/NEWS	1 Sep 2008 13:56:17 -0000
@@ -130,6 +130,11 @@ Now, the default behavior is to open a n
 Use the -c option to get the old behavior of opening files in the
 currently selected Emacs frame.
 
+*** Emacs can now start in background, as a daemon when using the
+--daemon command line argument.  It disconnects from the terminal and
+starts the server.  Clients can connect and create graphical or
+terminal frames using emacsclient.
+
 *** The new command close-display-connection closes a connection to a
 remote display.
 
Index: lisp/startup.el
===================================================================
RCS file: /cvsroot/emacs/emacs/lisp/startup.el,v
retrieving revision 1.503
diff -u -3 -p -r1.503 startup.el
--- lisp/startup.el	23 Aug 2008 16:59:19 -0000	1.503
+++ lisp/startup.el	1 Sep 2008 13:56:17 -0000
@@ -881,9 +881,11 @@ opening the first frame (e.g. open a con
 
   (run-hooks 'before-init-hook)
 
-  ;; Under X Window, this creates the X frame and deletes the terminal frame.
-  (when (fboundp 'frame-initialize)
-    (frame-initialize))
+  (if (daemonp)
+      (server-start)
+    ;; Under X Window, this creates the X frame and deletes the terminal frame.
+    (when (and (fboundp 'frame-initialize))
+      (frame-initialize)))
 
   ;; Turn off blinking cursor if so specified in X resources.  This is here
   ;; only because all other settings of no-blinking-cursor are here.
Index: src/emacs.c
===================================================================
RCS file: /cvsroot/emacs/emacs/src/emacs.c,v
retrieving revision 1.443
diff -u -3 -p -r1.443 emacs.c
--- src/emacs.c	23 Aug 2008 16:45:13 -0000	1.443
+++ src/emacs.c	1 Sep 2008 13:56:18 -0000
@@ -232,6 +232,9 @@ int noninteractive;
 
 int noninteractive1;
 
+/* Nonzero means Emacs was started as a daemon.  */
+int is_daemon = 0;
+
 /* Save argv and argc.  */
 char **initial_argv;
 int initial_argc;
@@ -1068,6 +1071,34 @@ main (int argc, char **argv)
       exit (0);
     }
 
+#ifndef DOS_NT
+  if (argmatch (argv, argc, "-daemon", "--daemon", 5, NULL, &skip_args))
+    {
+      pid_t f = fork();
+      int nfd;
+      if (f > 0)
+	exit(0);
+      if (f < 0)
+	{
+	  fprintf (stderr, "Cannot fork!\n");
+	  exit(1);
+	}
+
+      nfd = open("/dev/null", O_RDWR);
+      dup2(nfd, 0);
+      dup2(nfd, 1);
+      dup2(nfd, 2);
+      close (nfd);
+      is_daemon = 1;
+#ifdef HAVE_SETSID
+      setsid();
+#endif
+    }
+#else /* DOS_NT */
+  fprintf (stderr, "This platform does not support the -daemon flag.\n");
+  exit (1);
+#endif /* DOS_NT */
+
   if (! noninteractive)
     {
 #ifdef BSD_PGRPS
@@ -1719,6 +1750,7 @@ struct standard_args standard_args[] =
   { "-nw", "--no-windows", 110, 0 },
   { "-batch", "--batch", 100, 0 },
   { "-script", "--script", 100, 1 },
+  { "-daemon", "--daemon", 99, 0 },
   { "-help", "--help", 90, 0 },
   { "-no-unibyte", "--no-unibyte", 83, 0 },
   { "-multibyte", "--multibyte", 82, 0 },
@@ -2350,6 +2382,13 @@ decode_env_path (evarname, defalt)
   return Fnreverse (lpath);
 }
 
+DEFUN ("daemonp", Fdaemonp, Sdaemonp, 0, 0, 0,
+       doc: /* Make the current emacs process a daemon.*/)
+  (void)
+{
+  return is_daemon ? Qt : Qnil;
+}
+
 void
 syms_of_emacs ()
 {
@@ -2368,6 +2407,7 @@ syms_of_emacs ()
 
   defsubr (&Sinvocation_name);
   defsubr (&Sinvocation_directory);
+  defsubr (&Sdaemonp);
 
   DEFVAR_LISP ("command-line-args", &Vcommand_line_args,
 	       doc: /* Args passed by shell to Emacs, as a list of strings.