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I use: Emacs 26.1 on Windows 10 with tramp with plink/pscp to edit perl scripts on a remote Linux server

The scripts are executable (permissions 755).

When I load and then save them, if short time has passed, the permissions are preserved. However, when I don't save the buffer for somewhat longer time, it corrupts remote file permissions and set them to 666.

Even after switching off the saving of backups problem persists.

How do I fix that? Are there workarounds?

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  • I'm assuming your problem is related to auto-saving. You could try disabling it. – user12563 Jan 16 '19 at 18:55
  • Also see C-h v make-backup-files. If the backups are made by renaming, then there's a greater chance of the new file not acquiring the same attributes as the original file, so you might find that backup-by-copying is your answer. – phils Jan 16 '19 at 23:33
  • Switched off backup files. Will see if the issue arises again. – George Potapov Jan 17 '19 at 10:59
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So I got fed up and made this workaround. It just checks the file name of file that has been saved and set permissions based on path.

;;
;; workaround for TRAMP always corrupting file permissions
(defcustom file-mode-alist nil 
  "Automatically set file permissions based on filename.
Each element has the form (REGEXP . MODE)
where REGEXP is a regexp to match against your file name and
      MODE - (integer) file mode (permissions) to set.
Pairs are checked in order of appearance, first one to match is used.
"
  :type '(alist :key-type regexp :value-type integer)
  :group 'personal)
(setq file-mode-alist '(( "^/pscp:host:.+/lib/.*\\.pm$" . #o644)
                        ( "^/pscp:host:.+/web/.*\\.pl$" . #o755)))

(defun run-regexps (alist str)
  "Iterate over association list alist and try to match regexps with string str"
  (if (null alist) nil
    (let ((a (car alist)))
      (if (string-match (car a) str)
          (cdr a)
        (run-regexps (cdr alist) str)))))
(defun set-remote-permissions ()
  "Set permissions of remote file if filename matched against file-mode-alist"
  (let* ((fn (buffer-file-name (current-buffer)))
         (mode (run-regexps file-mode-alist fn)))
    (when mode (chmod fn mode))))

(add-hook 'after-save-hook 'set-remote-permissions)
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  • Additionally to your workaround, I would appreciate if you file a bug report. Together with a short recipe for reproduction, and/or proper traces, it might help to fix this problem. Consult the Tramp manual how to write a bug report. BR, Michael (Tramp maintainer) – Michael Albinus Jan 21 '19 at 14:57

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