Backup restoration vs metadata preservation in Emacs: which method retains file attributes?

Answer

When you use M-x revert-buffer, Emacs writes the backup file back to disk with the default filesystem attributes. The original file’s mode, ownership, and timestamps are lost. Emacs does not expose an option to preserve those attributes automatically.

Why revert‑buffer loses metadata

Reverting replaces the buffer’s contents with the contents of the most recent backup file and then writes that content back to the file’s path. The write operation is performed as a normal write-file call, which creates a new file (or truncates the existing one) with the permissions and times that the underlying filesystem assigns to a new file. No attempt is made to copy the old file-attributes over.

Reliable way to keep attributes

Capture the original attributes, revert, then restore them:

1. Store the attributes before the revert:

   (setq my/backup-attrs (file-attributes "~/path/to/file"))

2. Run M-x revert-buffer.
3. Reapply the attributes:

   (when my/backup-attrs
     (set-file-modes "~/path/to/file" (nth 3 my/backup-attrs))
     (set-file-times "~/path/to/file" (nth 6 my/backup-attrs)))

These two set-file‑* calls restore the mode and the last modification time. Ownership is not changed; if you need to preserve that you’ll have to run a command as the file’s owner or with sudo.

Automating the workflow

You can add a tiny hook that runs automatically whenever you revert a buffer:

(defun my/restore-attrs-after-revert (orig-fun &rest args)
  "Restore file attributes after a revert.")
  (let ((attrs (file-attributes (buffer-file-name))))
    (apply orig-fun args)
    (when attrs
      (set-file-modes (buffer-file-name) (nth 3 attrs))
      (set-file-times (buffer-file-name) (nth 6 attrs)))))
(advice-add #'revert-buffer :around #'my/restore-attrs-after-revert)

Place this in your init file if you frequently revert buffers and want to keep metadata intact.

Existing packages

There are no mainstream packages that provide this exact functionality out of the box. The snippet above is lightweight enough to include directly.

What you might still need to check

Do you also need to preserve file ownership, or are you working on a filesystem that ignores the access‑time field? If so, the logic above will need to be extended accordingly.