atomicc.rb: Don't assume we may chown/chmod a file.

Previously this code just assumed it is capable of changing the file
ownership, both user and group. This will fail in a lot of scenario's
unless:
* The process is run as a superuser (root);
* The owning user and group are already set to the user and group we're
  trying to chown to;
* The user chown'ing only changes the group to another group it is a
  member of.
If either of those conditions are not met the filesystem will simply
deny the operation throwing an error.

It is also not always possible to do a chmod, there might be a SELinux
policy or another limitation preventing the user to change the file
mode. To this end the chmod call has also been added to the rescue
block.

I've also added a little comment above the chmod command that doing a
chmod on a file which has an ACL set will cause the ACL to be
recalculated / modified.

1 files changed, 2 insertions, 0 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 4b06210c4a..83e763fd77 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 *   Implement HashWithIndifferentAccess#replace so key? works correctly. *David Graham*
 
+*   Handle the possible Permission Denied errors atomic.rb might trigger due to its chown and chmod calls. *Daniele Sluijters*
+
 *   Hash#extract! returns only those keys that present in the receiver.
 
         {:a => 1, :b => 2}.extract!(:a, :x) # => {:a => 1}