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I have a file setup.py created with Emacs and I set 744 permissions to it:

$ ls -la
total 8
drwxr-xr-x  3 user  staff   96 10 Dec 20:49 .
drwxr-xr-x  6 user  staff  192 10 Dec 20:47 ..
-rwxr--r--  1 user  staff   39 10 Dec 20:49 setup.py

When I edit the file so that Emacs auto-saves, it creates a linked file that represents a lock, which is also executable:

$ ls -la
total 8
drwxr-xr-x  4 user  staff  128 10 Dec 20:56 .
lrwxr-xr-x  1 user  staff   36 10 Dec 20:56 .#setup.py -> user@computer.local.587
drwxr-xr-x  6 user  staff  192 10 Dec 20:47 ..
-rwxr--r--  1 user  staff   39 10 Dec 20:49 setup.py

I save the file with Emacs, and the executable bit resets to 0:

$ ls -la
total 8
drwxr-xr-x  3 user  staff   96 10 Dec 20:56 .
drwxr-xr-x  6 user  staff  192 10 Dec 20:47 ..
-rw-r--r--  1 user  staff   40 10 Dec 20:56 setup.py

I have the same problem if I edit with -q, which skips initialisation:

$ chmod +x setup.py
$ emacs -q setup.py
2019-02-01 10:26:12.136 Emacs-x86_64-10_10[7566:50149] ...
$ ls -la
total 48
drwxr-xr-x  10 user  staff   320  1 Feb 10:26 .
drwxr-xr-x  15 user  staff   480 31 Jan 14:56 ..
-rwxr-xr-x   1 user  staff  2139  1 Feb 10:26 setup.py

The version is 26.1 (9.0).

How can I prevent Emacs from resetting the executable bit?

miguelmorin
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  • Do you see the same behavior if you start Emacs from `emacs -Q`? If not, bisect your init file to find the problem. – Drew Dec 10 '18 at 21:27
  • It may be that emacs version and version are important information for this question. Please add that information. – Tobias Dec 10 '18 at 22:10
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    Is `C-h i g (emacs)Backup Copying` a factor here? – phils Dec 11 '18 at 00:15
  • @phils Running `(setq backup-by-copying 't)` forced backup by copying instead of renaming and solved this issue. Do you want to write an answer? – miguelmorin Feb 01 '19 at 10:36

1 Answers1

3

As @phils mentioned in a comment, the reason is the default backup policy (from C-h i g (emacs)Backup Copying):

Backup files can be made by copying the old file or by renaming it.

...

The method of making a backup file may also affect the file’s owner and group. If copying is used, these do not change.

The solution is to change this setting in your init file:

(setq backup-by-copying 't)
miguelmorin
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