How do I change read/write mode for a file using Emacs?

Question

If a file is set to read only mode, how do I change it to write mode and vice versa from within Emacs?

Answer 1

Be sure you're not confusing 'file' with 'buffer'. You can set buffers to read-only and back again with C-x C-q (toggle-read-only). If you have permission to read, but not write, a file, the buffer you get when you visit the file (C-x C-f or find-file) will be put in read-only mode automatically. If you want to change the permissions on a file in the file system, perhaps start with dired on the directory that contains the file. Documentation for dired can be found in info; C-h i (emacs)dired RET.

Answer 2

M-x toggle-read-only

or in more recent versions of Emacs

M-x read-only-mode

On my Windows box, that amounts to Alt-x to bring up the meta prompt and typing "toggle-read-only" to call the correct elisp function.

If you are using the default keyboard bindings,

C-x C-q

(which you read aloud as "Control-X Control-Q") will have the same effect. Remember, however, given that emacs is essentially infinitely re-configurable, your mileage may vary.

Following up from the commentary: you should note that the writeable status of the buffer does not change the writeable permission of the file. If you try to write out to a read only file, you'll see a confirmation message. However, if you own the file, you can write out your changes without changing the permissions on the file.

This is very convenient if you'd like to make a quick change to a file without having to go through the multiple steps of add write permission, write out changes, remove write permission. I tend to forget that last step, leaving potentially critical files open for accidental changes later on.

Answer 3

What I found is M-x set-file-modes filename mode

It worked at my Windows Vista box. For example: M-x set-file-modes <RET> ReadOnlyFile.txt <RET> 0666

Answer 4

CTRL + X + CTRL + Q     

Answer 5

I tried out Vebjorn Ljosa's solution, and it turned out that at least in my Emacs (22.3.1) there isn't such function as 'trim-right', which is used for removing an useless newline at the end of chmod output.

Removing the call to 'trim-right' helped, but made the status row "bounce" because of the extra newline.

Answer 6

C-x C-q is useless. Because your also need the permission to save a file.

I use Spacemacs. It gives me a convenient function to solve this question. The code is following.

(defun spacemacs/sudo-edit (&optional arg)
  (interactive "p")
  (if (or arg (not buffer-file-name))
      (find-file (concat "/sudo:root@localhost:" (ido-read-file-name "File: ")))
    (find-alternate-file (concat "/sudo:root@localhost:" buffer-file-name))))

I call spacemacs/sudo-edit to open a file in emacs and input my password, I can change the file without read-only mode.

You can write a new function like spacemacs/sudo-edit.