jason@forever ~ $ ls -ald foo
-rw-r--r-- 1 jason jason 0 Apr 13 21:54 foo
jason@forever ~ $ rm foo
rm: remove write-protected regular empty file `foo'? yes
rm: cannot remove `foo': Operation not permitted
jason@forever ~ $ ls -ald foo
-rw-r--r-- 1 jason jason 0 Apr 13 21:54 foo
jason@forever ~ $ sudo rm foo
rm: remove write-protected regular empty file `foo'? yes
rm: cannot remove `foo': Operation not permitted