I use browse-url/browse-url-firefox to open links in Firefox from within Emacs 24.5.1 under Linux (Fedora 23) which in essence executes the firefox executable with the URL by start-process. If there is already a Firefox instance running, this will in turn cause the URL to be opened in a new tab and terminate the firefox executable spawned from Emacs, but otherwise a new Firefox instance will be running as a process child of Emacs (for testing purposes, this is equivalent to M-! sleep 1h & RET).

If I then want to exit Emacs, it asks me "Active processes exist; kill them and exit anyway?" with the option to either kill the Firefox instance or, well, leave Emacs running. Instead I would like to "detach" the firefox process from the Emacs parent so that I can exit Emacs while keeping the Firefox instance running.

Is it possible to spawn processes from Emacs that "survive" exiting Emacs, or must all spawned processes die when Emacs exits?

  • Are you running Emacs on a Windows machine by any chance? It sounds similar to an issue I never got an answer to from about 2 years ago -- How to delete a process from Emacs without killing the subprocess: stackoverflow.com/q/19747637/2112489 On OSX, for example, the behavior is different -- i.e., I can open an external application with start-process (like a pdf viewer) and Emacs thinks its job has finished. – lawlist May 19 '16 at 2:48
  • No, I'm using Linux (Fedora 23). I'll amend the question to reflect that. – Tim Landscheidt May 19 '16 at 4:19

here's solution, shorting @abo-abo's answer.

     ((string-equal system-type "windows-nt") ; Windows
      // ...
     ((string-equal system-type "gnu/linux")
      (start-process "my-browse"
                     nil "setsid"
                     (concat "file://" buffer-file-name ))

      ;; (browse-url ξurl)
     ((string-equal system-type "darwin") ; Mac
                // ...

Note that condition is necessary, because Mac doesn't have setsid.

  • See the answer here for an updated answer that should also work for Mac's – dalanicolai May 27 at 15:31

Currently the best way to achieve this (although it does not work for Windows) is by using the command call-process with the destination argument set to 0 (see https://www.gnu.org/software/emacs/manual/html_node/elisp/Synchronous-Processes.html).

E.g. to start firefox you could use:

(call-process "firefox" nil 0 nil "www.spacemacs.org")

Here's a command that does what you want:

(defun ora-dired-start-process (cmd &optional file-list)
   (let ((files (dired-get-marked-files
                 t current-prefix-arg)))
      (unless (eq system-type 'windows-nt)
        (dired-read-shell-command "& on %s: "
                                  current-prefix-arg files))
  (if (eq system-type 'windows-nt)
      (dolist (file file-list)
        (w32-shell-execute "open" (expand-file-name file)))
    (let (list-switch)
       cmd nil shell-file-name
        "nohup 1>/dev/null 2>/dev/null %s \"%s\""
        (if (and (> (length file-list) 1)
                 (setq list-switch
                       (cadr (assoc cmd ora-dired-filelist-cmd))))
            (format "%s %s" cmd list-switch)
        (mapconcat #'expand-file-name file-list "\" \""))))))

(define-key dired-mode-map "r" 'ora-dired-start-process)

The key thing here is to use nohup.

See the source here.

  • Thanks! nohup is a nice solution. Unfortunately I find your answer too "distracting" for someone just looking for how to achieve the goal. Could you please trim the source down to something like (shell-command "nohup sleep 1h &") and add an explicit note that "detaching" from an existing process is not possible so that I can accept the answer? – Tim Landscheidt May 22 '16 at 4:36
  • I was told 'setsid' was better than 'nohup'. – YoungFrog May 22 '16 at 6:07

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