I want to use emacs auto-save feature with tramp, but only for file that I don't open using sudo. My current configuration, based on the tramp documentation, looks like this:

;;;;;;;; BAKUCP ;;;;;;;;
;; Backup remote files locally to stop autosave pain
(setq tramp-backup-directory "~/.emacs-backup")
(unless (file-directory-p tramp-backup-directory)
  (make-directory tramp-backup-directory))
(if (file-accessible-directory-p tramp-backup-directory)
    (setq tramp-auto-save-directory tramp-backup-directory)
  (error "Cannot write to ~/.emacs-backup"))
;; Don't backup su and sudo files
(setq backup-enable-predicate
      (lambda (name)
        (and (normal-backup-enable-predicate name)
              (let ((method (file-remote-p name 'method)))
                (when (stringp method)
                  (member method '("su" "sudo"))))))))

It is forbidding creating remote backups of files edited as superuser but auto-saved files are still created on my local machine. Is there any way to disable that without disabling auto-save at all?

1 Answer 1


Backup and auto-save are different operations, controlled by different variables.

If you want to discard auto-save for files opened as root, you might change the buffer-local variable auto-save-file-name-transforms. Something like this (untested):

 (lambda ()
   (when (and (stringp buffer-file-name)
          (string-equal (file-remote-p buffer-file-name 'user) "root"))
     (setq buffer-auto-save-file-name nil))))
  • If you put this in the users' .emacs file, it will not be read if emacs is opened with sudo though correct? So when would this code be in effect?
    – Startec
    Aug 16, 2016 at 19:34
  • I don't understand your question. Everything in ~/.emacs is evaluated at start of Emacs, unless you start Emacs with the -Q or similar option. Aug 17, 2016 at 7:25
  • Sorry, I meant that opening emacs with sudo emacs would not read the config file in the users' home directory. I realize now this is probably a good answer for when something is opened as sudo from an instance of emacs opened as a user.
    – Startec
    Aug 17, 2016 at 7:32
  • What variable would check if the file were opened as root? (i.e. opened with the /sudo::/ tramp method)?
    – Startec
    Aug 17, 2016 at 7:33
  • default-directory is a buffer-local variable, which tells you the current directory of that buffer. (file-remote-p default-directory) returns non-nil, when you are remote. (file-remote-p default-directory 'user) gives you the remote user name, "root" for example. Aug 17, 2016 at 8:58

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