backup-by-copying-when-privileged-mismatch applies to file gid, too.

* lisp/files.el (backup-by-copying-when-privileged-mismatch):  In addition
to checking the file uid, a second test is added: if the file gid is not
greater than backup-by-copying-when-privileged-mismatch,
backup-by-copying-when-mismatch will also be forced on.

* doc/emacs/files.texi, doc/lispref/backups.texi: Updated documentation.

Also fixed a typo in the Emacs reference manual, changing "higher" to
"no greater" so that the limit is no longer documented reversed.

1 files changed, 9 insertions, 6 deletions

diff --git a/lisp/files.el b/lisp/files.el
index a384e7136e8..96f1e8d47e7 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -134,10 +134,11 @@ This variable is relevant only if `backup-by-copying' is nil."
 (defcustom backup-by-copying-when-privileged-mismatch 200
   "Non-nil means create backups by copying to preserve a privileged owner.
 Renaming may still be used (subject to control of other variables)
-when it would not result in changing the owner of the file or if the owner
-has a user id greater than the value of this variable.  This is useful
-when low-numbered uid's are used for special system users (such as root)
-that must maintain ownership of certain files.
+when it would not result in changing the owner of the file or if the
+user id and group id of the file are both greater than the value of
+this variable.  This is useful when low-numbered uid's and gid's are
+used for special system users (such as root) that must maintain
+ownership of certain files.
 This variable is relevant only if `backup-by-copying' and
 `backup-by-copying-when-mismatch' are nil."
   :type '(choice (const nil) integer)
@@ -4634,8 +4635,10 @@ BACKUPNAME is the backup file name, which is the old file renamed."
                                       (let ((attr (file-attributes
                                                    real-file-name
                                                    'integer)))
-                                        (<= (file-attribute-user-id attr)
-                                            copy-when-priv-mismatch))))
+                                        (or (<= (file-attribute-user-id attr)
+                                                copy-when-priv-mismatch)
+                                            (<= (file-attribute-group-id attr)
+                                                copy-when-priv-mismatch)))))
                              (not (file-ownership-preserved-p real-file-name
                                                               t)))))
                    setmodes)