Guy's

we are in AIX 5.3

We have created two users user1 and user2 and they are under same group Staff Group

user1 will create file under /tmp/ and this is the permission of this file

-rw-r--r-- 1 user1 staff 1 Jun 13 09:47 file

user2 is under same group and when he try to change the permission of the same file he will get this message !

chmod 777 file
chmod: file: Operation not permitted.

I know the owner of the file is user1 but user1 and user2 are under same group so should have same permission

is there any clue to let the change of the permission be executed by user2 ?